The Cladocera of Suffolk. by Suffolk Naturalists' Society

SUFFOLK CLADOCERA CHECKLIST

THE CLADOCERA OF SUFFOLK ADRIAN CHALKLEY The aim of this article is to stimulate interest in the recording of Cladocera or water fleas in our county. In order to do this it is best to outline the ecological importance of these relatively overlooked and unappreciated animals, this will be followed by a brief glimpse of their geological past and some details of general Cladoceran life histories. Information about recording and a provisional Suffolk species list concludes the introduction and finally there is a review of all species in the British list showing those that have been recorded in Suffolk or may be possible to find in the future, whilst putting them in context with national records as far as is known. Cladocera and the Ecology of Freshwaters Water fleas (Crustacea: Branchiopoda: Cladocera) occupy a wide range of niches globally and are some of the most successful invertebrates found in freshwater ecosystems. Cladocerans can be found within the zooplankton of all types of freshwaters from puddles to large lakes, from ditches to major rivers. As a group they are of prime importance within aquatic food webs across the globe often occurring in high abundance, showing a marked degree of morphological diversification and species richness. Whilst there are some species which predate other zooplankton the majority of cladocera feed on phytoplankton; to be eaten in turn by higher invertebrates, amphibians and fish. Unlike most freshwater plankton, Cladocera have the distinction of being widely known to the general public as ‘Daphnia’. In reality this recognition can be more of a disadvantage since the Daphnia are but one of the 14 families that make up the Cladocera Crustacea. In this article I will outline some of the reasons for studying these tiny, but vital, members of the Freshwater food chain. Cladocera through time The cladoceran fossil record is neither very extensive nor, until recently, very well researched and the pre-quaternary record is generally relatively sparse. After all they are tiny, the majority being less than 1mm with an exceptional few reaching 5 to 6mm, and are difficult to identify from compression fossils in sedimentary rocks. However recent research mostly using fossil ephippia (resting eggs) has extended this sparse record back into the Jurassic (Van Damme & Kotov 2016). These tantalizing micro fossils show that the basic cladoceran body plan and life history was well established at least before the majority of dinosaurs appeared. Then having survived the mass extinction which wiped out the dinosaurs cladocera have continued to the present day in a remarkably unbroken manner. Generalised Cladoceran life history For a large proportion of the year dipping a fine mesh net into most water bodies will rarely catch anything but female water fleas. These are parthenogenetic females which spend their short lives feeding and giving birth to many more parthenogenetic females. Overwintering females or resting eggs may well be in relatively small numbers but exploit spring blooms of phytoplankton. This enables large populations to quickly establish which are exploited in turn by a host of carnivorous members of Trans. Suffolk Nat. Soc. 56 (2020)

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A. Chalkley

the aquatic community. During the course of the year it is apparent that various stressors may cause these parthenogenetic females to spontaneously produce gamogenetic offspring, i.e. both male and female, which can mate sexually. Finding male water fleas is in fact a reasonably rare and notable occurrence for the freshwater ecologist. At this point of course there is a population of both male and female forms, and mating often occurs before a general population crash. Mated gamogenetic females will now produce resting eggs called ephippia, instead of live offspring. Ephippia are the means of dispersal in cladocera, avoiding genetic bottlenecks and the method by which they have persisted for so long.

Daphnia magna ephippia 1.35mm (in a mud sample from Hen Reedbeds). Ephippia: the secret of success. Some aquatic invertebrates such as beetles, bugs and caddis flies are able to fly in order to colonise new habitats, those which cannot have had to evolve a method of dispersal. In cladocera the ephippia provides a superb example of such a mechanism. In ephippia resting eggs are encased in a protective outer covering formed from part of the dorsal chitinous carapace of the mother (Dumont & Negrea, 2002) they are very strong and remain viable for long periods. Some of these resting eggs sink slowly to be buried in the substratum where they are frequently found within sediment cores drilled from lake bottoms. The longevity of ephippia is astounding, such cores have been radio-carbon dated to as much as 1600 years and ephippia at depths as old as 700 years have been hatched and new colonies bred (Weider et al., 2014). Instead of sinking other ephippia float on the water surface to be caught in waterfowl feathers or are merely swallowed, resistant to gut acids they can later hatch in large numbers if the bird’s droppings land and are dissolved in freshwater (Proctor, 1964). This is but one possible reason for the unexpected occurrence of water fleas in temporary waterbodies such as puddles or rainwater butts, though in stormy weather the wind may also transport the eggs. Of course dog walkers who let their pets swim

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in a local pond or lake and then drink from a puddle also provide a perfect method of transport. It is always worth examining puddles and water filled ruts in woodland or farm tracks for the presence of water fleas. However, water fleas are not only reliant on ducks or dogs. Any animal, large or small, with feathers or fur will provide a similar dispersal mechanism, which is something that cladocera have exploited throughout their history. In the permafrosts of Siberia, Prof. Alexey Kotov has found enormous numbers of ephippia in the fur and gut contents of sub-fossil wooly mammoths and rhinos, showing that cladocera were spread from pool to pool across the tundra by these enormous creatures. Given that cladocera pre-dated the dinosaurs and that recent dinosaur fossils have shown many to have been feathered, this suggests the intriguing possibility that cladocera were also dispersed by dinosaurs. It has been shown (Haag et al., 2005) that whilst the colonization of empty habitat patches could of course cause genetic bottlenecks, the short-term colonisation of small temporary ponds or pools can be stepping stones for successive rounds of immigration to older, permanent waterbodies leading to increased genetic diversity. This, along with the rapid increase in population size due to parthogenesis, allows cladocera to adapt to habitat change. (Weider et al., 2014) showed that populations of Daphnia pulicaria in South Center Lake, Minnesota, USA, quickly evolved to cope with increased phosphate pollution after 1894; the phosphate influx being caused by runoff from the introduction of newly developed artificial fertilisers on nearby farms. The species remained and is still extant, but changes in DNA to adapt took place in relatively few short years. Recording Cladocera Given their importance within the aquatic ecosystem it is a shame more people do not record them. As with all branches of freshwater science a good key is the first requirement followed by the right equipment. At present the best English key is still by Scourfield & Harding (1966), although this is now out of print it is still available from several second-hand dealers. When used with the downloadable key in French by Amoros (1984) and the revised British species list, both available from www.cladocera.org.uk , all UK species can be identified. Because of the small size of these animals, most people will need nets designed for plankton of one design or another with mesh sizes somewhat smaller than the usual 1mm, usually 500 microns or less. Professionally made these are very expensive, but amateur enthusiasts often make their own, home wine making filter bags often being a good source of netting. The other major requirement is a good microscope to observe and identify. Whilst many naturalists will already possess a stereo microscope for use with larger invertebrates, such as beetles, these instruments are usually only of use for the initial sorting of specimens. It is almost always necessary to view individual water fleas on a glass slide with cover slip through a compound microscope with magnifications of several hundred times to accurately identify the smaller parts detailed below in the species accounts.

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A Checklist of Cladocera recorded in Suffolk as of October 2020 Listed below are 52 species out of the 92 on the British list which have been recorded within Suffolk. In addition there are 14 underlined and marked ##, which have no records as yet but are possible future additions to this county list. Numbers in brackets show for each family the number of species recorded out of the total number in that family, e.g. (20/24). For more information see the individual species accounts which follow. Family Species Leptodoridae (0/1) None Sididae (2/3) ## Diaphanosoma brachyurum (Lieven, 1848) ## Sida crystallina (Müller, 1776) Holopedidae (0/1) None Daphniidae (18/24) Ceriodaphnia dubia Richard, 1894 ## Ceriodaphnia laticaudata Müller, 1867 ## Ceriodaphnia megops Sars, 1862 Ceriodaphnia pulchella Sars, 1862 Ceriodaphnia quadrangula (Müller, 1785) Ceriodaphnia reticulata (Jurine, 1820) Ceriodaphnia setosa Matile, 1890 Daphnia ambigua Scourfield, 1946 Daphnia atkinsoni Baird, 1859 Daphnia cucullata Sars, 1862 Daphnia curvirostris Eylmann, 1887 Daphnia hyalina Leydig, 1860 Daphnia longispina Müller, 1785 Daphnia magna Straus, 1820 Daphnia obtusa Kurz, 1874 Daphnia pulex (DeGeer, 1778) ## Megafenestra aurita (Fischer, 1849) ## Scapholeberis mucronata (Müller, 1785) Simocephalus exspinosus (Koch, 1841) ## Simocephalus serrulatus (Koch, 1841) ## Simocephalus vetulus (Müller, 1776) Moinidae (1/3) Moina brachiata (Jurine, 1820) Bosminidae (2/3) Bosmina longirostris (Müller, 1785) Bosmina longispina Leydig, 1860 (species inquirenda?) Ilyocryptidae (2/3) ## Ilyocryptus agilis Kurz, 1878 ## Ilyocryptus sordidus (Lieven, 1848) Eurycercidae (1/2) Eurycercus lamellatus (Müller, 1785)

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SUFFOLK CLADOCERA CHECKLIST Family Chydoridae (22/42)

Ophryoxidae (0/1) Acantholeberidae (0/1) Macrothricidae (3/6)

Polyphemidae (1/1) Cercopagidae (0/1)

Species ## Acroperus angustatus Sars, 1863 ## Acroperus harpae (Baird, 1835) Alona affinis (Leydig, 1860) Alona costata Sars, 1862 Alona guttata Sars, 1862 ## Alona intermedia Sars, 1862 ## Alona quadrangularis (Müller, 1785) Alonella excisa (Fischer, 1854) Alonella exigua (Lilljeborg, 1853) Alonella nana (Baird, 1843) ## Anchistropus emarginatus Sars, 1862 ## ## Camptocercus lilljeborgi Schoedler, 1862 ## ## Camptocercus rectirostris Schoedler, 1862 ## Chydorus ovalis Kurz, 1874 Chydorus sphaericus (Müller, 1785) Coronatella rectangula (Sars, 1862) Disparalona rostrata (Koch, 1841) ## Dunhevedia crassa King, 1853 ## Graptoleberis testudinaria (Fischer, 1848) ## Kurzia latissima (Kurz, 1874) ## ## Leydigia acanthocercoides (Fischer, 1854) ## Leydigia leydigi (Schoedler, 1862) Oxyurella tenuicaudis (Sars, 1862) Pleuroxus aduncus (Jurine, 1820) Pleuroxus denticulatus Birge, 1879 Pleuroxus trigonellus (Müller, 1785) Pleuroxus truncatus (Müller, 1785) Pleuroxus uncinatus Baird, 1850 Pseudochydorus globosus (Baird, 1843) Tretocephala ambigua (Lilljeborg, 1900) None ## Acantholeberis curvirostris (Müller, 1776) ## Lathonura rectirostris (Müller, 1785) Macrothrix laticornis (Jurine,1820) Macrothrix rosea (Jurine,1820) Polyphemus pediculus Linnaeus, 1761 None

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Cladocera species accounts. In the following section CIG is used as an abbreviation for the Cladocera Interest Group, whose website can be found at www.cladocera.org.uk It is probably best to read the species accounts with one eye on the following website which has photos of most of our British species: ‘An Image-Based Key to the Zooplankton of North America’ http://cfb.unh.edu/cfbkey/html/species.html Both national and county distribution data are taken from both the CIG and the SBIS databases. The species are presented in the order given in the updated British list 2011/2012, downloadable from the CIG website. Species Accounts The accounts below summarize each species in the British list published online by the Cladocera Interest Group (CIG). The description of each species draws heavily on the contributions of CIG members; on Scourfield & Harding (1966), and Fryer (1993). Data given for each species recorded in Suffolk is from my own database up to and including October 2020. However it must be emphasized that with the present level of recording the absence of data for any species does not, except in a few special cases, preclude its future discovery in our county. The summary of national data for each species is drawn from both the CIG database and the NBN Atlas. However, as in much biological recording, the number of records & their distribution can say more about where the recorders live & have recorded. There has been no attempt to attribute a status to most species in the way that some invertebrate groups such as the Coleoptera have an IUCN designation. However, the revised CIG British list ascribes the status of Species inquirenda to 4 species of doubtful validity which have appeared in previous lists but are without any verified British records. The use of the term in English-language biological literature dates back to at least the early nineteenth century. Leptodoridae Leptodora kindti (Focke, 1844) Glass Waterflea Suffolk: No records UK: 142 records A planktonic waterflea which is only found floating in the open waters of lakes, reservoirs and gravel pits, Leptodora kindti is one of the most transparent creatures in nature. Larger than most water fleas at up to 18mm in length, like Polyphemus pediculus the carapace or shell covers only the brood chamber in which its eggs are hatched. L. kindti is a true predator of smaller crustaceans and due to its transparency and mode of living has been mostly recorded from plankton nets towed or vertically hauled from a boat, but it is unmistakable once caught. Records are few and scattered north from London reservoirs towards Leicester, with several from Wales, many from the Lake District and a scattering of locations throughout Scotland.

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Sididae Diaphanosoma brachyurum (Lieven, 1848) Suffolk: 0 record UK: 308 records Diaphanosoma brachyurum is a highly transparent species, like many of its family it has a long oval outline roughly twice as long as broad. It has no rostrum on the rounded head, which is about a third of the body in size, with a large compound eye. The first pair of antennae are particularly long. Tending to be found in open waters it is often planktonic. It is widely distributed across more or less the whole of the British Isles, but most records come from Wales, North West England, the Lake District and Scotland, data from Ireland and the South being more scattered. First recorded near Suffolk, by Claude Morley in 1903 from Fritton Decoy but with several records from nearby sites in Norfolk and Cambridgeshire, including the Breckland Meres in 1972 and Wicken Fen in 1928 and 1973. The Breckland Meres were surveyed by Raymond Watson and from notes made when I borrowed his M.Phil. Thesis he made the following observations: “Diaphanosoma brachyurum was equally common at all sites. … It did not appear to be affected by fish stock in the Breckland Meres, being sufficiently transparent to be unaffected” “Diaphanosoma brachyurum was found in the water for only a short period in the summer and resting eggs formed the entire winter population. It does not produce an ephippium and eggs of this species could not be distinguished from other eggs found in the mud. It was hatched from several sites.” Latona setifera (Müller, 1785) Suffolk: No records UK: 59 records Latona setifera is our only member of the genus Latona, it has no rostrum and is distinctive in having the eye set on the dorsal surface of the head, almost as if it were looking behind, it is also a long oval shape almost twice as long as broad. The antennae have numerous long bristles and it moves faster than any other waterflea. Usually it lives close to the bottom in the littoral zone but sometimes to moderate depths in larger lakes. It can be quite transparent but with age chromatophores (pigmented cells) develop which may be red, blue or brown. Easily seen brilliantly coloured old females appear seasonally, along with autumn leaves along the shore line. Not a common or abundant species the most recent records are some 40 years old now. First recorded in 1893 from Loch Morar, subsequent records are from Ireland, North Wales, the Lakes, Central Scotland, the Western Isles and Shetland. Sida crystallina (Müller, 1776) Crystal Waterflea Suffolk: 8 records UK: 297 records The common name long used for Sida crystallina comes from the transparency of this species but in truth this applies to all of the family Sididae of which S. crystallina is just the best known. Like the rest of the family it has a long oval body shape but it is the only one with a rostrum. It has a visible gland on the back of the head, with which it is able to attach itself to the vegetation amongst which it lives, especially to the

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underside of Potamogeton. It lives in lakes, ponds, some rivers or canals with clear water and is widely distributed. Although it can be abundant in suitable ponds it is not all that common everywhere. Records are scattered right across the British Isles, from Cornwall to the North of Scotland and the Western Isles, from Ireland to the East Coast. In Suffolk it has been found at Cribbensgate Lake at Flatford and in the River Stour at various sites. It occurs in reservoirs at Lound, in dykes at Carlton Marshes, Oulton marshes and Bulcamp Marshes at Blythburgh. Holopedidae Holopedium gibberum Zaddach, 1855 Jelly Waterflea Suffolk: No records UK: 65 records Holopedium gibberum is so different from all other cladocerans that it cannot be mistaken for anything else being the only species that is always covered by a gelatinous sheath or mantle in which it lives. The carapace or shell covers only the brood chamber in which its eggs are hatched and it normally swims upside down with the jelly covering supporting its body. It is completely planktonic and only recorded from larger bodies of freshwater such as the Lochs and Lochans of Scotland, Cumbrian lakes and a small number of Welsh lakes. Usually transparent it can be hard to see but sometimes when suitable phytoplankton food is plentiful it can have patches of red or blue.

Daphniidae Ceriodaphnia dubia Richard, 1894 Suffolk: 2 records UK: 61 records Ceriodaphnia are a genus which resembles the typical Daphnia form but have a distinctly smaller head lacking the obvious rostrum of most Daphnia and have short antennules. Identification of C. dubia, as with the rest of the genus, relies on microscopical observation of the morphology of the postabdomen. C. dubia occurs in the plankton of the littoral zone of ponds and lakes, usually amongst a rich phytoplankton on which they feed. In the British Isles as a whole records are widespread but more numerous in the South East, Midlands and Wales, being at present rather sparse elsewhere. The two Suffolk records are from one lake at Elveden in 2008 and from Framlingham Mere in 2013. Ceriodaphnia laticaudata Müller, 1867 Suffolk: 0 records UK: 130 records Ceriodaphnia laticaudata tends to inhabit the margins of ponds and lakes, feeding on decaying plant matter rather than phytoplankton. It has a more rounded head and a postabdomen which is wide and rounded in the center. More common across the British Isles than C. dubia with widespread records from England south of a line from Blackpool to Hull, from Wales, from Ireland and Scotland too. The only near Suffolk location was a record from Fritton Decoy by Claude Morley in 1902.

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Ceriodaphnia megops Sars, 1862 Suffolk: 3 records UK: 118 records This species has a larger compound eye than other Ceriodaphnia, no comb of teeth on the claw and the postabdomen has a distinctive step near the distal end. C. megops is found most often in smaller ponds, ditches or larger water bodies and seems to prefer well vegetated habitats. A littoral species it can be planktonic in open water or taken amongst weed beds near the shore line. Nationally it is widely distributed with the majority of records in an area South East of a line from Weymouth to the Wash. Elsewhere data is more scattered as far north as the Lake District and with a handful of sites in Ireland. Near Suffolk there is a single record from Fritton Decoy in 1903, as usual by Morley, and the old NRA found it in Barn Creek, Flatford in 1961. Since then it has only been taken in 1992 in two of the lakes at Center Parcs, Elveden but subsequent surveys until 2019 did not find it again. Ceriodaphnia pulchella Sars, 1862 Suffolk: 17 records UK: 219 records As stated above the genus Ceriodaphnia has a smaller head than the Daphnia and has no rostrum. However, C. pulchella differs in that it does have a bulge above the first antenna (antennule) in the position where a rostrum is normally situated, and the postabdomen is also very distinctive. Said by Scourfield & Harding (1966) to occur in the open water of ponds and to be planktonic in lakes most Suffolk records have been from lakes with abundant phytoplankton. It would seem to be common across the British Isles especially in the South East, North Wales and the Lake District. There is a scattering of records from Southern Ireland and Scotland as far as the Orkneys. Suffolk records are from all the larger lakes at Center Parks, Elveden in surveys from 1992 until 2010 but not thereafter! Claude Morley found it first of course in 1903 from Fritton Decoy and Oulton. Also from Holbrook Lake, Boxford in 2013 and from a dyke in Bushes Marshes Oulton in the same year. Ceriodaphnia quadrangula (Müller, 1785) Suffolk: 6 records UK: 344 records Widespread and common across the British Isles, Ceriodaphnia quadrangula is another species in the genus with no comb on the claw. It can be distinguished because the postabdomen has a slightly concave dorsal margin, the postabdomen is also quite long and is often projecting from the carapace. Found in water bodies of all sizes, usually those rich in phytoplankton. Near to Suffolk it was found in Fritton Decoy by Morley in 1903 and in the early days of the FSC at Flatford Mill in 1958. More recent records are from 3 of the lakes at Center Parcs Elveden Forest between 2007 and 2009 and from a dyke at Bushes Marshes at the SWT Reserve of Oulton Marshes in 2013. Ceriodaphnia reticulata (Jurine, 1820) Suffolk: 20 records UK: 181 records Being the only species of the genus with a comb of teeth near the base of the abdominal claw, this is easy to identify. As the name implies, Ceriodaphnia reticulata

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has a carapace or shell which is reticulated, though this can be indistinct and may test the skill of the microscopist in lighting the subject correctly, in any case other Ceriodaphnia can also have reticulation. Found in waters of varying sizes it is often found to be planktonic. Although usually within the littoral zone of large lakes, it may also be found in emergent and floating leaved vegetation. Generally common across the British Isles though records are more numerous in the South East, North Wales and north to the Lake District; elsewhere it seems to be more scattered. In common with several other cladocerans Suffolk records begin in 1903 at Fritton Decoy with Claude Morley, there are several early FSC records from 1958 / 1959 from ponds and a lake at Flatford Mill. More recent data is from a number of both newly restored and neglected ponds across the county as well as reservoirs like the ones at Lound and dykes and marsh drains at Oulton and Carlton Marshes. Ceriodaphnia setosa Matile, 1890 Suffolk: 1 record UK: 4 records Ceriodaphnia setosa is the only species of this genus with small spines (prickles) over the surface reticulation of the carapace. It is said to always be amongst water weeds and the few sites where it has been found do bear this out. C. setosa is rare in the British Isles having been found only 4 times: Twice at Wicken Fen in Cambridgeshire in 1930 and 1932 by A. G. Lowndes, once in a Breckland Mere by Raymond Watson in 1979, once in 2008 by Faye Merrix in the Cardiff Bay Wetlands Reserve and once by myself in 2014 in a dyke at Oulton Marshes. There is also a record given in (Scourfield & Harding, 1966) for East Ruston Common in Norfolk which seems to have been omitted from John Hearn’s data when that was sent by the CEH to the Cladocera Interest Group so it may be he viewed it as doubtful. Daphnia ambigua Scourfield, 1946 Suffolk: 2 records UK: 9 records Daphnia ambigua is presumably ambiguous in that having claws without combs it is a member of the longispina group, and yet the spine at the bottom of the carapace is very short or absent! This species is most likely introduced and not native. Originally found in Kew Gardens and in Regents Park in 1905. Very rare indeed in the British Isles the 9 records on the CIG provisional atlas are more or less in a straight line running north east from the original site to a recent record from Framlingham Mere in Suffolk in 2013. In Suffolk it was also found in a pond in Leavenheath in 2016. Other data is all from the London area and Epping Forest. Daphnia atkinsoni Baird, 1859 Suffolk: 1 record UK: 40 records Daphnia atkinsoni is one of only two species in the magna group and is easy to distinguish from D. magna due to the distinctive postabdomen of the latter. It is rare and is mainly found in rich alkaline ponds and ditches. First recorded in Yorkshire in 1886, from where around 8 more records have been made. Elsewhere across the British Isles there are sporadic records from around the London area and the South East. The most modern records were made by John Bratton from North Wales in 2001

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and his 4 records from Lincolnshire near the Humber from 2004, 2007, 2013 and 2016. In and near Suffolk there are only two records, from Herringfleet in 1901 and just across the border in Fritton Decoy in Norfolk in 1903 both by Claude Morley. It has not been found since despite sampling Cladocera in the vicinity. Daphnia cucullata Sars, 1862 Helmeted Waterflea Suffolk: 6 records UK: 91 records The common name for this waterflea refers to the fact that it is one of the two Daphnia species which has a pointed or rounded crest extending the head upwards and slightly backwards. This is often best seen with the animal laying ‘face down’ under the microscope and viewing the head from behind. D. cucullata has no ocellus, a blunt rostrum and long setae on the antennule. Often found in lakes with fish and a rich phytoplankton population, it is an open water species usually taken by either trawling or vertically hauling a plankton net. It is widely distributed across England and Wales though there are only records from the Scottish mainland. In Suffolk, it has been found recently in all the lakes at Center Parcs, Elveden but has only been found otherwise at Fritton Decoy in 1903 and Breydon in 1920. Daphnia curvirostris Eylmann, 1887 Suffolk: 9 records UK: 109 records Having a comb of teeth at the base of the abdominal claw puts Daphnia curvirostris into the pulex group of the genus along with D. pulex and D. obtusa. Separating these three species is largely a matter of microscopically observing the shape of the rostrum and the number of teeth in the comb. Across the British Isles D. curvirostris has been found in several larger waterbodies and reservoirs but for Suffolk the preferred habitat seems to be smaller, shallow ponds and marshes. A large number of archive data are in the South East but most new records made since 2000 have been from North Wales, Lincolnshire and a single one from the Lakes. It has not been found in Scotland and only one archive record was from Southern Ireland. In Suffolk it was first found in East End Pond at Flatford in 1958 and since 1993 in farm and village ponds as well as several turf ponds at the SWT Oulton Marshes Reserve. Daphnia galeata Sars, 1864 Pointed-helmeted Waterflea Suffolk: No records UK: 31 records The common name for this waterflea refers to the fact that it is one of the Daphnia species which has a pointed crest extending the head upwards and slightly forwards. This should be clearly seen with the animal laying ‘on its side’ under the microscope. This species keys out as D. hyalina var. galeata in Scourfield & Harding (1966) but is now regarded as a distinct species since the updated British list from the CIG in 2012. It may be separated from D. hyalina using Amoros (1984). A planktonic species originally recognized from Lake District archive data especially from Windermere and recorded in the last few years from several reservoirs and lakes in Wales and Cumbria as well as Scotland, including the Orkneys. In addition it has also been found in some small ponds including the wildlife pond in the Natural History Museum, South Kensington.

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Daphnia hyalina Leydig, 1860 Suffolk: 7 records UK: 300 records Daphnia hyalina is very widespread and common across the whole of the British Isles including Ireland and the Scottish Islands including the Hebrides and Orkneys but not yet from Shetland. Almost in Suffolk it was first found in Fritton Decoy, 1903 by Morley, then from two small pools at Redgrave Fen in 2002, from a dyke at Carlton Marshes in 2005, two of Center Parcs Elveden Forest artificial lakes in 2007 and from Cribbensgate Lake at Flatford Mill in 2015. Daphnia longispina Müller, 1785 Long-tailed Waterflea Suffolk: 99 records UK: 717 records Daphnia longispina is one of the Daphniidae which has no comb on the claw nor a crest to the head. Normally found as a planktonic species in lakes it is also often found in the littoral zone of smaller sites or in the weed or leafy debris of puddles, woodland ponds etc. Across the British Isles the species is common with records generally widespread from the Scilly Isles through England and Wales as far north as Hull, beyond this most data has been collected from the Lake District, the Central belt of Scotland and then scattered through the highlands and the Scottish Islands as far north as Shetland. In Suffolk it is also common and widespread; occurring in all types of freshwater from muddy woodland puddles or ponds, from farm ponds, dykes and many of the turf ponds at Oulton Marshes as well as lakes and reservoirs across the county. Daphnia magna Straus, 1820 Large Waterflea Suffolk: 15 records UK: 195 records The magna group of Daphniidae differs from the pulex or longispina groups in the shape of the dorsal part of the head shield. To see this, especially the lateral projections, it is best to perch the specimen ‘face down’ under the stereo microscope with transmitted light under the head. Daphnia magna is a large species with such a distinctive postabdomen (or tail) that identification should be no problem. Scourfield & Harding (1966) list it as being “In warm waters in small ponds or little bays of larger waters. Rather rare, S & E England”. Records on the CIG database reflect his habitat notes and the bias of a South East England distribution but there are also scattered records through the Midlands to North Wales and up the East Coast as far as the North Yorkshire Moors. In Suffolk it is not all that common, and the first nearby records came from Fritton Decoy and Ploughman’s Ham, near Oulton in 1905, again by Morley. Elsewhere the recorded habitat is small ponds in Woodland, Gardens or Farms and some lakes such as Framlingham Mere and those at Center Parcs Elveden Forest. Daphnia obtusa Kurz, 1874 Suffolk: 69 records UK: 548 records Daphnia obtusa is part of the pulex group of Cladocera, those with combs on the abdominal claws. It is easily separated from the others by the bulge underneath the rostrum from which the antennule grows and either a short ventral spine or none.

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SUFFOLK CLADOCERA CHECKLIST

The typical waterflea of your local duck pond and very common across most of the British Isles, though records are sparse north of the Lake District, in Northern Ireland and Scotland. In Suffolk it is very common in garden ponds and those in woods or farms as well as ditches and puddles.

Daphnia pulex (DeGeer, 1778) Common waterflea Suffolk: 39 records UK: 357 records The archetypal waterflea in many naturalists’ minds and one of the species with a comb on the abdominal claw. Identification relies on observation of the teeth on this comb and the shape of the rostrum and antennule. Typically a lowland species of smaller ponds and ditches but it may be found in the littoral zone of larger ponds or some lakes. Across the British Isles it is widespread D. pulex Vale pool Postabdomen-claw and very common especially from Lands’ (From a pond in Birmingham, shows the End to a line roughly from Liverpool to postabdominal claw with the two combs the Humber. It occurs in lowland areas arrowed, one with 5 teeth other with 6 only so much of Wales is blank in diagnostic. No scale, but whole animal is distribution maps and further north the about 2mm) few records are very sparse. In Suffolk data runs from 1903, Morley of course, to 2020. The data is widespread from puddles in woods or farm tracks; from village ponds or those in woods, farmland or gardens and from the occasional small lake. Daphnia rosea Sars, 1862 Suffolk: No records UK: 8 records When the new British list was being compiled for the CIG the late Jim Green gave this advice; “Daphnia rosea is regarded as a good species in North America, and Brooks (1957) mentions its occurrence in England. I have seen specimens agreeing with Sars original description. I would leave this on the new CIG list, although some people do not regard it as being separable from D. longispina” Jim Green (Pers. Comm.) So when

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Daphnia parvula Fordyce, 1901 Suffolk: No records UK: 2 records Added to the 2012 British list published by the CIG after being found by Mary Morris in 2009 in Round Pond on Chobham Common and by the late Jim Green from Broom Water near Teddington Lock in 2012. No other records have been made of this species but further details on identification can be downloaded from the CIG website (Green, 2012). Jim wrote “Originally from North America, D. parvula is now widespread in continental Europe, and is thought to have been introduced on amphibious vehicles brought to Europe by the US army during the Second World War”.

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identifying D. rosea one does need to be very careful to be aware of this similarity. The only known records of D. rosea come from Clare Brook, Cambridge in 1948 by D. S. Johnson and 7 from WIcken Fen, Cambridgeshire by John Hearn in 1982 and 1986.

Scapholeberis mucronata (Müller, 1785) The Meniscus Waterflea Suffolk: 55 records UK: 403 records As detailed above Scapholeberis mucronata has a short, rounded rostrum and also swims upside down hanging under the surface whilst drawing nutrients from the surface film into its mouth. For this reason it is always a good idea when trawling with a plankton net to include at least one pull with part of the net cutting the surface, although S. mucronata tends to dive down when disturbed it will then dive into the net as S. mucronata Oulton Marshes. it passes. S. mucronata often develops a (swims upside down under surface film) backward pointing, horn like extension to the dorsal surface of the head shield in response to predation, this form was named by Scourfield (1966) as S. mucronata forma cornuta. Its mode of feeding requires fairly calm, still waters and so records from larger waterbodies tend to be from sheltered bays or among emergent vegetation. Exposed sites such as mountain tarns therefore provide few records. It is widely distributed and common across the British Isles, including Southern Ireland, from Cornwall to Scotland. However data for Wales and Highland Scotland is much more scattered and may well be explained by the need for a calm habitat. In

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Megafenestra aurita (Fischer, 1849) Suffolk: 0 records UK: 15 records Megafenestra aurita will key out to Scapholeberis aurita in many older keys and both Megafenestra aurita and S. mucronata are very similar in appearance. The major difference being that the rostrum is long and pointed in M. aurita and short and rounded in S. mucronata. The generic name Megafenestra refers to an oval window like plate on the dorsal surface of the head, which can only be seen using high magnification and careful lighting. Both species are unusual in that they are mostly found suspended beneath the surface film on top of the water by means of the tiny setae along the straight ventral margins of the shell. M. aurita is rare indeed and was last recorded over 70 years ago. The two local records on our database were made by Claude Morley in 1903 and 1904 at Herringfleet on the Suffolk- Norfolk border. Other nearby data for the British Isles comes from the Breckland Meres in 1979 by Raymond Watson, and otherwise the only known sites are Newborough, near Peterborough, Hartlebury Common near Kidderminster and Leighton Moss RSPB reserve.

SUFFOLK CLADOCERA CHECKLIST

Suffolk it is found in most of the Center Parcs Elveden Forest lakes which are tree bordered and very calm, the same applies to Cribbensgate Lake in Flatford. Other sites are mostly small farm or roadside ponds, dykes and turf ponds at Oulton marshes or fen habitats. Simocephalus exspinosus (Koch, 1841) Small-headed Waterflea Suffolk: 32 records UK: 280 records All three Simocephalus species have a very small rostrum as implied by the common name but it is best to check the lines marking the carapace or shell. These are parallel, oblique lines for Simocephalus and squares for Daphnia species. S. exspinosus has an ocellus which is squarish or at worst a slightly oval blob distinguishing it from S. vetulus below. The edge of the head (the frons) in front of the eye is rounded and it has a comb of teeth on the base of the claw. S. exspinosus is very much the waterflea you might expect in small weedy ponds, though it is slightly rarer than S. vetulus. Records are sparser from the Midlands and the South West but this may be more due to the distribution of recorders. It has always seemed rarer north of the Lake District and there are few recent Scottish records, elsewhere it is widespread including Southern Ireland. In Suffolk it is less common than the similar S. vetulus, but is widespread across the county in small ponds of all sorts, a few larger waterbodies like Framlingham Mere or the lakes at Elveden Forest and even some slower sections of rivers such as the Little Ouse. In Suffolk it is happy in brackish water such as the Hen Reedbeds and it has even been found in pools in the shingle spit at the National Trust’s Orford Ness reserve, the site of the World War two radar station, which are a stone’s throw from the sea and its most easterly site in the UK. Simocephalus serrulatus (Koch, 1841) Marsh Small-headed Waterflea Suffolk: No records UK: 22 records In Simocephalus serrulatus the edge of the head (the frons) in front of the eye is pointed and extended into an angular shape, the edge of the frons is not smooth but there are 2 to 4 small spine like teeth. This distinguishes it from S. exspinosus and S. vetulus where the frons would be rounded and smooth. Rarer than the other members of this genus it has been recorded from fens, bogs and marshy sites, from North Wales, Southern Ireland and the Isle of Man. Two records from Swaffham Prior Fen in 1976 and Holme Fen in 1982, both in Cambridgeshire but the former very close to Newmarket raises the possibility of finding it in a suitable Suffolk habitat. Simocephalus vetulus (Müller, 1776) Small-headed Waterflea Suffolk: 184 records UK: 1217 records Simocephalus vetulus has an unusual ocellus which is an elongated, slightly wavy streak easily distinguishing it from S. exspinosus above. The edge of the head (the frons) in front of the eye is rounded and smooth and it is without a comb of teeth on the base of the claw. S. vetulus may well be the most common cladoceran in the British Isles and certainly the most common in Suffolk. Nationally, apart from an absence of records from the Scottish Highlands, it is widespread everywhere including

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the Hebrides, the Isle of Man and the Scilly’s. Almost any size and type of freshwater may be found to contain S. vetulus from temporary puddles and ponds to large lakes, reservoirs and flooded quarries. Unusual records include being found in the hyporheos or ground water of a chalk stream by Richard Chadd of the Environment agency. This was Laceby Beck in Lincolnshire in water pumped from 1.5 metres down in the chalk / sand substrate, using a Bou-Rouche pump. I myself have found it in the outflow of a pump taking water from a Simocephalus well some 60 feet deep used to irrigate a orientations strawberry farm in Lindsey, Suffolk. Obviously an adventurous and tough species indeed!

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vetulus

Moinidae Moina brachiata (Jurine, 1820) Suffolk: 4 records UK: 35 records Older keys, such as Scourfield & Harding (1966), will key out Moina rectirostris as well as M. brachiata, the former being a synonym of the latter. All Moina have some similarities with Daphnia but have no rostrum, a larger head and large antennule, M. brachiata being the only species with a comb on the claw. Often it is found in rather stagnant and turbid pools, small ponds and muddy puddles. Nationally there are no records further north than Southport or Spalding and elsewhere are very widespread, but thinly scattered. In Suffolk Claude Morley found it in 1903 from sites at Herringfleet and Hopton, since then there have been two records, both from fairly typical wood edge ponds, rather turbid but with plenty of submerged vegetation, at Suffolk Wildlife Trust’s Arger Fen reserve and from a farm in nearby Boxford. M. brachiata Arger Fen

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group

various

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SUFFOLK CLADOCERA CHECKLIST

Moina macrocopa (Straus, 1820) Suffolk: No records UK: 20 records Moina macrocopa is a rare species occasionally found in shallow, muddy pools with few other cladocerans. It can be distinguished from M. brachiata as it does not possess a comb on the claw. Nationally there are a few old records scattered very widely from Epping Forest, West Norfolk, Yorkshire, Rotherham and St David’s; more recently the species has only been found in North Lincolnshire 2014 – 2016 and from a lake south of Inverness in 2012. Moina micrura Kurz, 1874 Status: Species inquirenda Suffolk: No records UK: No records Moina micrura was retained on the British list when it was updated in 2012 in the hope that increased recording would find it. To date there have been no records and it remains listed as Species inquirenda. It can be recognized by the depression in the outline of the head behind the eye and from the postabdomen which has less than 8 postanal spines. Bosminidae Bosmina coregoni Baird, 1857 Baltic Long-nosed Waterflea Suffolk: No records UK: 72 records This species has often been confused with Bosmina longispina, however it is doubtful that the true B. longispina does occur within the UK (see below). The 72 records on the NBN Atlas are all from Wales which is where I myself have found it. It tends to be found in the epilimnion of stratified lakes with a high fish population, it is a very unlikely find in Suffolk but identification details can be found on line (Soesbergen, 2016) Bosmina longirostris (Müller, 1785) Common Long-nosed Waterflea & Bosmina longirostris var. cornuta (Jurine)Horned Common Long-nosed Waterflea Suffolk: 83 records UK: 281 records This species is found across Suffolk in lakes, reservoirs and ponds of all sizes and is probably much more common than the number of records may suggest. Across the UK it is often associated with nutrient rich lowland lakes with a high density of fish. Note the cornuta form tends to develop in the presence of fish predation. Bosmina longispina Leydig, 1860 Rare Long-nosed Waterflea Status: Species inquirenda Suffolk: 1 record UK: 26 records As has been outlined above there are great similarities between Bosmina coregoni and B. longispina and the Cladocera Interest Group originally gave the status of ‘Species inquirenda’ to B. longispina on their revised species list until specimens could be confirmed by experts. Since 2012 there have been 27 likely records made which seem to be sufficiently morphologically different from B. coregoni, including a single record from Cribbensgate Lake at Flatford. The other 25 records are from Wales, the North West and Scotland. A final decision on the status of B longispina awaits analysis. Trans. Suffolk Nat. Soc. 56 (2020)

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Ilyocryptidae Ilyocryptus acutifrons Sars, 1862 The Mud Waterflea Suffolk: No records UK: 25 records The three species of the Ilyocryptidae are very distinctive looking and all live in the bottom mud of waterbodies, a good impression of their anatomy can be gained by downloading the article cited below from the CIG. The study of the genus Ilyocryptus was at its height in the late 19th and early 20th Century, by which the reader may rightly infer that recent records are few. The first records of Ilyocryptus acutifrons were made from Loch Shin in Scotland by Sir John Murray and Laurence Pullar (Murray & Pullar, 1910), in England the first records were made by William John Plunket Smyly across 13 Lake District sites from 1955 to 1984. That there were no records made after Smyly is explained by the fact that this species lives half buried in the mud, at the bottom of lakes. In 2016, 60 years after the last record made by Smyly at Overwater in Cumbria, Soraya Alvarez and Melanie Fletcher from the Freshwater Biological Association revisited the site and, having resurrected from the FBA stores the original equipment used to survey the lake, I. acutifrons was still living happily in the bottom mud! The equipment used to find the Mud Waterflea from out of a boat at the bottom of a 59 foot tarn is called the Gilson well sampler. Full details of their survey are available to download from the CIG website (Alvarez & Fletcher, 2016). No other records of this species are known and whilst it may be doubtful if mud at the bottom of Suffolk lakes would be a suitable habitat, for any readers with DIY skills details of the Well Sampler and other methods can be found at https://hcrs.brc.ac.uk/sampling-methods on the Hypogean Crustacea Recording Scheme website. Ilyocryptus agilis Kurz, 1878 The Yellow Mud Waterflea Suffolk: No records UK: 16 records In common with other species in the genus Ilyocryptus agilis lives its life hidden in the mud, but unlike I. acutifrons it is a littoral species so can be found near lake shores amongst weeds and is usually yellow- brown in colour. Although there are more records for this species because of this relative ease of sampling the distribution is very poorly known. Known from Surrey, Herts, Middlesex, Oxfordshire, East Norfolk, Leicestershire, Wales and Scotland; first recorded in 1848 in Norfolk and last found in 1993 in South Wales. A possible unrecorded Suffolk species? Ilyocryptus sordidus (Lieven, 1848) The Red Mud Waterflea Suffolk: 1 record UK: 212 records Ilyocryptus sordidus is fairly common and widespread as the number of records indicates. Always red in colour it also lives in the bottom mud and is said to be incapable of swimming, though it burrows through the bottom mud or debris covering a sand substratum to filter out food. Widely distributed but unlikely to be easily spotted in a plankton or other net haul it is best deliberately searched for. Many older records lie in a band from the South West to East Anglia, others are in Wales and up the west coast of England to Cumbria, scattered through Scotland including the Western Isles and Shetland. In Suffolk it has been found once by Claude Morley at Oulton in 1903. Trans. Suffolk Nat. Soc. 56 (2020)

SUFFOLK CLADOCERA CHECKLIST

Eurycercus lamellatus (Müller, 1785) Giant Crawling Waterflea Suffolk: 67 records UK: 859 records Eurycercus lamellatus as the common name implies is, at up to 4mm, probably the largest water flea most people are likely to find. In older keys it was placed in the family Chydoridae which it resembles in overall appearance. Very common indeed and widespread over all parts of the British Isles it is an important food item for fish. It can be found in all types of waterbodies and in Suffolk it has been recorded from cattle troughs, Fen and Marsh drains, Turf Ponds, garden ponds, lakes or reservoirs and rivers. E. lamellatus Lound (a large species. The Wherever it is found it tends to be a brood pouch here is empty, she gave birth littoral species favouring weed beds after she was caught) rather than a bare substratum, although in sites like Cribbensgate Lake at Flatford Mill it can often be taken amongst leaf debris and other detritus. It is adapted well for climbing over plants and feeds by scraping algae and sediments from plant surfaces. Because of its size it produces large ephippia which may often be found in the mud of a site, even though adults may be missing at the time. Chydoridae Acroperus angustatus Sars, 1863 Flat-backed Duck Waterflea Suffolk: No records UK: 12 records Acroperus angustatus closely resembles the next species A. harpae, except that the dorsal margin of the shell is flat rather than strongly arched. A transparent species found in weeds or open water in a variety of still habitats. Although not recorded in

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Eurycercidae Eurycercus glacialis Lilljeborg, 1887 The Arctic Waterflea Suffolk: No records UK: 9 records Eurycercus glacialis is very rare, being an ice age relict species only recorded a few times from remote sites in Scotland. First discovered in 1957 at Morrich More, East Ross-shire, where it was found again in 1988. Subsequent recording effort established that it also still survived on Ronas Hill on Shetland. It was recorded again in 2003 at Queina Water, also on Shetland, and in 2011 at Water of Hoy in the Orkneys. Since 2018 Kenny Gifford has established more lochs and lochans on Shetland where E. glacialis seems to thrive. Since the common species E. lamellatus has a very similar appearance separating the two takes a good deal of skill with the microscope. Excellent images of both are available on Kenny’s website www.shetlandlochs.com and details of identification can be found in CIG Newsletter 4 (Bratton, 2013).

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Suffolk there are 5 past records of this species in Norfolk and 1 from Cambridgeshire so it may possibly repay searching for. However it does seem to be rare across the rest of the British Isles with very few other records emanating from the Thames, The Lake District and Roundstone in Ireland. Common Duck Waterflea

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Acroperus harpae (Baird, 1835) Suffolk: 12 records UK: 540 records Acroperus harpae has a strongly arched dorsal margin to the shell, somewhat resembling a harp in overall shape. A transparent species it is found in weeds or open water in a variety of still habitats. The Suffolk records are from a variety of places including man-made lakes at Elveden, ponds adjacent to the River Fromus, Lackford lakes, and ponds beside the River Tang and from Flatford Mill pond. Across the British Isles it occurs widely, literally from Lands’ End to Shetland.

A. harpae (From Cribbensgate Lake, Flatford. Parthenogenetic female carrying two eggs in the brood pouch - not Ephippia - which are arrowed).

Alona affinis (Leydig, 1860) Beaked Waterflea Suffolk: 12 records UK: 625 records As a species Alona affinis is very tolerant of pH being found in between pH 3.9 to pH 9.1, it will also cope with brackish water and varying levels of vegetation cover. One of the largest species in the genus it closely resembles A. quadrangularis with which it may be confused since both inhabit the littoral zone of a waterbody though A. quadrangularis seems to be less tolerant of low or high pH. It is widespread and common across the British Isles; from Cornwall to the Orkneys, from the West coast of Ireland to the Suffolk coast. Across the county A. affinis has been found in the zooplankton of 9 different lakes, reservoirs and small farmland ponds. Alona costata Sars, 1862 Striped Beaked Waterflea Suffolk: 2 records UK: 98 records A distinctive species with a long, slender, and sharply angled postabdomen. Not common anywhere, Alona costata can be found in both small pools and large lakes. It may have a preference for medium to high conductivity and is reported as favouring algae-rich habitats being found close to the substrate. Certainly a species worth searching for across the county. Both Suffolk records for A. costata are from the same site at Lound Lakes in June and September 2006. It would seem to be widespread across the British Isles with sparse records from most areas of England, Wales, Scotland and Ireland.

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SUFFOLK CLADOCERA CHECKLIST

Alona elegans Kurz, 1874 Fine-striped Beaked Waterflea Suffolk: No records UK: 1 records Alona elegans is a bit of a mystery. Known presently from only one pond on Dartmoor, taken in March 1976, October 1979 and then in May 1981. This only known location is a shallow acidic pool of pH 5.25 with little littoral vegetation which is often turbid due to the activities of sheep and ponies from the moor. No records after 1981 were made and the species was listed as species inquirenda at the time of the 2012 update to the British list. However thanks to the efforts of CIG member Phil Greaves it was rediscovered, still inhabiting the original pond, in January 2020. The only other British records were made in Yorkshire in 1903 and Norfolk in 1905 both from small, possibly temporary roadside ponds. So, very much a mystery species but worth bearing in mind when coming across suitable habitat, which could well look small, temporary, muddy and distinctly unpromising to the surveyor! Alona guttata Sars, 1862 Dwarf Beaked Waterflea Suffolk: 1 record UK: 260 records Alona guttata is a species very likely to turn up anywhere in the littoral zone of ponds and lakes often in or on a muddy substrate. It appears to tolerate a wide range of pH but it has been suggested that higher conductivity waters are favoured. The 260 records of A. guttata that the CIG database has are widely scattered over the British Isles roughly from London to the central belt of Scotland. Irish data are only from the southern half of the country. Just outside the Suffolk border is a record from Fritton Decoy in 1903 by Claude Morley and it was found by myself in a small but natural lake in Boxford in 1993. It could be quite possible to turn it up in suitable habitat anywhere in the county. Alona intermedia Sars, 1862 Beaked Waterflea Suffolk: No records UK: 68 records Alona intermedia is one of the smallest Alona species but with a distinctively wide postabdomen and long basal spines to the claws. Although no Suffolk sites have been found for Alona intermedia, there is one record from Salle, near Aylsham in Norfolk in 2012. Across the British Isles records are widespread but very scattered, although that is probably due to a paucity of recorders. Scourfield found it to be more common in Scotland (Scourfield & Harding, 1966) Alona karelica Stenroos, 1897 Russian Beaked Waterflea Status: Species inquirenda Suffolk: No records UK: No records Alona karelica has been cited as a native species on many early British lists, but no reliable records or specimens are known from this country. Along with A. weltneri it has been redescribed (Van Damme, 2011) and Kay Van Damme (Pers. Comm.) feels that it may yet possibly be found in UK Sphagnum Bogs. On this advice and with the absence of actual records A. karelica was kept into the CIG list as species inquirenda. Possibly a true relict species.

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Alona quadrangularis (Müller, 1785) Scrambling Waterflea Suffolk: 1 record UK: 294 records A relatively large species in the genus, Alona quadrangularis closely resembles A. affinis with which it may be confused, and both inhabit the littoral zone of a waterbody. As a species it is less tolerant of pH than A. affinis being found between pH 5.6 to pH 7.9. Across the British Isles it is very widespread; from Cornwall to the Orkneys, from the West coast of Ireland to coastal Suffolk although it is not common anywhere. There is an archive record of A. quadrangularis from Fritton Decoy in 1903 and specimens were taken at Lackford Lakes in 2012. Alona rustica Scott, 1895 Beaked Waterflea Suffolk: No records UK: 141 records Known as an indicator of acid lakes this small littoral species is often associated with sphagnum which explains the lack of Suffolk data and its general rarity in Southern and Eastern England. It is widespread across Ireland, Wales, North West England and Scotland including Shetland and the Hebrides. Alona weltneri Keilhack, 1905 Narrow-striped Beaked Waterflea Suffolk: No records UK: 2 records Alona weltneri was first recorded in 1907 by Scourfield but remains extremely rare. There is a possibility that it is true relict species and the only site where it has been found, both in 1979 and 1981, is in Kirkintilloch, in the Forth and Clyde Canal. Alonella excisa (Fischer, 1854) Striped Dwarf Beaked Waterflea Suffolk: 7 records UK: 342 records A littoral species almost always found in water weeds it is one of the most adaptable cladocerans tolerant of a wide range pH values, can colonise acidic conditions and can even cope with mildly brackish water. This is a widespread and common species across the British Isles with records in all areas of England, Wales, Ireland as well as the Scottish mainland and islands; being in fact one of the very few cladocerans found on St Kilda in 1956. Suffolk samples have been collected from Lakes at Elveden & Framlingham Mere, small farm ponds at Boxford and the rivers Lark, Gipping and Stour. Alonella exigua (Lilljeborg, 1853) Grey Dwarf Beaked Water Flea Suffolk: 3 records UK: 85 records Alonella exigua morphologically exhibits a great similarity with A. excisa requiring close examination of the postabdomen, shell reticulation and ventral-posterior shell teeth to distinguish. Because of these similarities it is quite possible that older data may in fact have confused the two species as the distribution of A. exigua, although sparser than A. excisa, is broadly similar geographically. Favoured habitats are also weeds in the littoral zone with a broad range of pH though possibly preferring higher conductivity than A. excisa. Records are sparse, many in southern England with other clusters in the Lake District, central Scotland and the Scottish Islands. The three Suffolk records are all close to Hadleigh, from a backwater of the River Brett in 1993, a farm pond at Milden in 2004 and a woodland pond in Raydon in 2016. Trans. Suffolk Nat. Soc. 56 (2020)

SUFFOLK CLADOCERA CHECKLIST

Alonella nana (Baird, 1843) Striped Dwarf Beaked Water Flea Suffolk: 3 records UK: 389 records Alonella nana is the smallest of the cladoceran species at 0.3mm, it is somewhat less transparent than many and under the microscope the shell shows very distinct striping. It occurs in a great variety of habitats, including those close to the sea which are not brackish and tolerates a broad range of pH and conductivity. National data is very widespread over all of the British Isles but as usual says more about where recorders are based than anything else. A. nana is known from 2 archive records from Hopton, south of the Little Ouse in 1919 and 1925. It was found once again in 2015 in groundwater weeps at the Suffolk Wildlife Trust Bromeswell Green Reserve. There are several archive records from the Norfolk Broads at the turn of the century and from East Wretham Heath in Breckland and a cluster around Wicken Fen in Cambridgeshire from the 70s & 80s. All indications are that A. nana could therefore be fairly common in Suffolk but may be overlooked. It should certainly be a target littoral species for those interested in studying Suffolk Cladocera. Alonopsis elongata Sars, 1862 Oblong Waterflea Suffolk: No records UK: 456 records Alonopsis elongata is somewhat similar to Acroperus harpae but has clear differences in the form of the postabdomen. Another littoral species it is reportedly more common in lakes than small ponds and ditches with A. elongata favouring sites with elevations above 500m. This species is indeed common in the British Isles but only from the west of Ireland, Wales, the north west of England as well as Scotland and the Scottish islands. Anchistropus emarginatus Sars, 1862 Siphon Waterflea Suffolk: No records UK: 13 records Few cladocerans have developed a taste for a protein-rich diet, and only two genera have adopted a carnivorous lifestyle, Anchistropus and Pseudochydorus. Anchistropus is often but wrongly called a “parasite “of Hydra and polyps do constitute the main diet. Using strong hooks on the first trunk limb, these chydorids tear ectodermal tissue off the cnidarians eventually killing them. “Anchistropus should, however, be called a carnivore, not a parasite. It is lethal to its prey and may quickly destroy a population of Hydra after which it will itself decline” (Hyman, 1926). A. emarginatus should therefore be looked for wherever one would find Hydra, for example searching through waterweeds in well vegetated drainage ditches. The rarity of Anchistropus, at least partly, may be attributed to the tight physical attachment of the animal to its prey, which makes it difficult to dislodge and collect. Possibly the best technique could be to let weeds stand in a glass tank overnight before examining the glass for hydra, possibly with attached Anchistropus. Although there are no records of this interesting species in Suffolk it remains well worth looking for in suitable habitats despite its rarity across both the British Isles and indeed Europe. A. emarginatus is after all easily overlooked due to its small size <0.5 mm, and its unusual way of life. The few UK records come from the neighbouring

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counties of Norfolk, Cambridgeshire and South Essex as well as from Yorkshire, the Lake District and the first known site of the Paisley Canal, Glasgow, in 1863. The most recent record is from near Derby in around 1968. Camptocercus lilljeborgi Schoedler, 1862 Narrow Stilt Waterflea Suffolk: No records UK: 4 records The two species of Camptocerus are similar in size and shape and both have a very long and narrow postabdomen which sets them apart from the other Chydoridae. Camptocercus lilljeborgi has the narrower postabdomen of the two with more than 20 teeth (denticles) along the ventral edge, C. rectirostris has less than 20 teeth on a less narrow tail. Elsewhere across its range C. lilljeborgi may be found in varying types of vegetation though rarely on a sandy or stony substratum. It is very rare in the UK and the only local data are from Potter Heigham and Barton Broad in 1898 and in 1903 from Sutton Broad in Norfolk. One other record comes from Wickham Fen in 1976. An unlikely find in Suffolk but all Camptocerus specimens should be carefully examined. Camptocercus rectirostris Schoedler, 1862 Broad Stilt Waterflea Suffolk: No records UK: 60 records Suitable habitats for C. rectirostris are similar to C. lilljeborgi in the littoral region of lakes or ponds but it is said to be more likely to be found on the substrate and in stands of Carex. As explained above C. rectirostris has less than 20 teeth on its slightly broader tail. Archive records also come from Potter Heigham and Barton Broad in 1898 as well as from Wroxham and one from Wickham Fen in 1928. This archive data comes from particularly well regarded recorders so once again an unlikely find in Suffolk but all Camptocerus specimens should be carefully examined. Elsewhere data are widespread with most early records from Wales and Scotland and two recent records from Cardiff Bay, 2008 and Congleton, 2016. Chydorus gibbus Sars, 1890 Humped Ball Waterflea Status: Species inquirenda Suffolk: No records UK: No records Evidence for the existence of Chydorus gibbus in the UK rests on a single record from Glasgow University visits to the Isle of Canna in the Inner Hebrides, 1936 and 1937. Habitat conditions on Canna throw much doubt on the accuracy of this identification (Bratton, 2014) and so the species retains its extremely doubtful status. Chydorus latus Sars, 1862 Large Ball Waterflea Status: Species inquirenda Suffolk: No records UK: 30 records Chydorus latus was last recorded, by a single recorder, from various ponds in Surrey, the Isle of Wight and Oxford in 1971 and 1974. All 16 previous records were made in the 1890s. However doubt has been cast on the accuracy of this data (Chalkley, 2016). The species is now regarded as species inquirenda, unproven to exist in the UK and in the past was probably confused with C. ovalis and / or C. sphaericus.

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SUFFOLK CLADOCERA CHECKLIST

Chydorus ovalis Kurz, 1874 Oval Ball Waterflea Suffolk: 4 records UK: 167 records Chydorus ovalis is often confused with C. sphaericus as both are very similar in size and shape and it takes very close examination to differentiate the two. C. ovalis has 8 setae in a terminal cluster plus 2 outlying setae on the antennule, which is more than both C. sphaericus and indeed C. latus. In addition ovalis has more than 10 denticles on the postabdomen whilst C. sphaericus has less than 10. C. ovalis shows a definite preference for peaty or boggy pools and for habitats with at least a slight degree of acidity but may occasionally occur in neutral waters. Elsewhere the most recent records are from Norfolk, Wales and Orkney but archive records dating back to 1898 are widespread across the UK. In Suffolk it has been recorded from Flatford Mill in 1958, from Wherstead and Carlton Marshes in 2006 and in 2012 at Lackford. Common Ball Waterflea

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Chydorus sphaericus (Müller, 1785) Suffolk: 97 records UK: 1,912 records Probably the most common waterflea across the British Isles Chydorus sphaericus is easily confused with C. ovalis as described above. As a species it is very tolerant of a great variety of conditions and can be found in waterbodies of all sizes and types from large lakes to small puddles. In many areas a good method of finding it is to squeeze handfuls of wet sphagnum into your net. In Suffolk it can be found in farm ponds and lakes, puddles in woods and even in the very brackish shingle pools on Orford Ness!

C. sphaericus Arger Fen (with eggs in the brood pouch, each with an air bubble unfortunately!)

Coronatella rectangula (Sars, 1862) Suffolk: 1 record UK: 154 records Coronatella rectangula was called Alona rectangula in earlier lists and was placed into this genus in 2012 when the British list was updated (Van Damme, Kotov & Dumont, 2010). Like the majority of Chydorids it is a littoral species, is most common in waters above pH 7.0 and can be found in freshwaters of all sizes. Our first local record comes from 1903 when Claude Morley found it in Fritton Decoy. However, in the late 1970s it was found in several of the Breckland Meres and also from Wicken Fen in the early 1980s. Other records are widespread across Ireland, England and the Scottish west coast. Disparalona rostrata (Koch, 1841) Crooked Beaked Waterflea Suffolk: 8 records UK: 52 records In some older keys this will key out to Rhynchotalona rostrata, but the name change was detailed as long ago as in the appendix to Scourfield & Harding (1966). With its

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elongated body, antennae having 7 setae and long, slightly backward curving rostrum (though not curved back as far as Rhynchotalona falcata) Disparalona rostrata is easy to recognize. It is not common and only a few of the records on the CIG database were made since 2000. Typically it is found in large ponds, lakes or reservoirs and occasionally canals. A bottom dweller, stones with or without a covering of mud are a good place to search by lifting rocks then scraping and washing off into the net. Across England new records are all located in a band from Norfolk to the Bristol Channel but older data are more widespread from Southampton to the Lake District. Some old records come from the West of Ireland but strangely very few from Wales. In Suffolk it has been found in a fishing lake in Boxford from 1992 to 2006, ponds by the River Tang in 1994, Framlingham Mere in 2000, lakes at Elveden and Lound reservoir in 2007. Dunhevedia crassa King, 1853 Suffolk: No records UK: 6 records Dunhevedia crassa is not keyed out in Scourfield & Harding (1966) but is in Amoros (1984). However, it has been shown to occur in the UK and notes on the morphology and British records can be downloaded (Bratton, 2011). Little information is available about the preferred habitat of this species as it has only been found and reliably recorded in one location, the Breckland Meres. It is likely though that this is a species of temporary waters. In fact one other archive record does exist from Hartlebury Common near Birmingham in 1932 but the recorder is unknown and accuracy of identification uncertain. All records from Breckland were made by Raymond Watson in his M.Phil. Thesis from the UEA. Some years ago Raymond lent me his thesis to read and these are his comments from notes I made: “Dunhevedia crassa as a species in the Breckland meres is rarely found in the water though ephippia are often found in mud.” “Ephippia were found in all the larger meres and the mere on Larling Heath and adults were hatched from Bagmore Pit mud. Ephippial females were found at Ringmere. Ephippia hatched readily in the laboratory.” Graptoleberis testudinaria (Fischer, 1848) Gliding Waterflea Suffolk: 6 records UK: 309 records Small, but relatively easily distinguished from other Chydorids, Graptoleberis testudinaria has a wide, spatula shaped, upturned rostrum on the head. It occurs in water bodies of all sizes and most types of vegetation or on stony or sandy substrata. Looking at the British Isles as a whole data is very widespread; from the West coast of Ireland to the Norfolk coast, from Lands’ End to Shetland but few of these are recent records. Archive records in Suffolk are from ponds at Hopton, more recently from a lake at Boxford and from Framlingham Mere. There are also records from neighbouring counties including from the Breckland Meres where Raymond Watson in his M.Phil. Thesis reported that he had hatched adults from the mud of Bagmore Pit, Langmere and Home Mere. It is a species which will certainly repay more recording effort in Suffolk.

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Kurzia latissima (Kurz, 1874) Taper-tailed Waterflea Suffolk: No records UK: 4 records Kurzia latissima is a rare and little understood species which is only known from records made from the Breckland Meres by Raymond Watson in his thesis for an M.Phil. from the UEA. From the notes I made after reading his thesis these comments of his are relevant: ‘Kurzia latissima as a species in the Breckland meres is rarely found in the water though ephippia are often found in mud.’ It is worth noting that Raymond also hatched adults from mud of Bagmore Pit, Langmere and Home Mere. Leydigia acanthocercoides (Fischer, 1854) Club-footed Waterflea Suffolk: No records UK: 6 records Both species of Leydigia have a distinctively broad almost semicircular postabdomen and an ocellus the same size as, or larger than, the eye. L. acanthocercoides can be separated as the claw has no basal spine. As can be seen from the amount of UK data it is rare, recorded as archive records from the Norfolk Broads in 1898 and found slightly more recently from Breckland in 1979, Wicken Fen in 1984 and Slapton Ley 1985. Leydigia leydigi (Schoedler, 1862) Suffolk: 4 records UK: 93 records In contrast to L. acanthocercoides above, L. leydigi is much more widely distributed and is said to mainly be found in the upper layer of bottom sediment often at some depth in lakes and large ponds. The first local record was by Claude Morley from Fritton Decoy in 1903. Since then I have found it twice in the same lake in Boxford in 1993 and 2013 where it was not common, nor was it found in the intervening years. It was also present in one of the Elveden Forest lakes in 2005. Monospilus dispar Sars, 1862 Mantled Waterflea Suffolk: No records UK: 47 records Monospilus dispar is relatively rare but widely distributed within its range despite having obvious identification features. It has only an ocellus and no compound eye, because of incomplete moulting it retains previous carapaces giving the mantled or humped back appearance. Usually found on the sand or mud bottoms of lakes it may be caught in vertical hauls of a plankton net from the lake bed. D.J. Scourfield found it in Eagle Pond, Snaresbrook in 1840 and 1897. Since then this species has only been recorded from the West of the UK, from Wales, the Lake District and Scotland with one record from Ireland. There has only been one recent record, by Faye Merrix during her PhD between 2006 and 2008 at the Cardiff Wetlands Reserve. Oxyurella tenuicaudis (Sars, 1862) Suffolk: 2 records UK: 50 records In earlier lists Oxyurella tenuicaudis was shown as Alona tenuicaudis. Originally placed in the genus Alona because of similarities with A. quadrangularis, although it is much

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larger. Usually found in small to medium ponds rich in aquatic vegetation, it is not common anywhere and records are very widespread with much archive data from the South East, including East Anglia. There are only 3 recent records, from Anglesey 2014 and the tip of mainland Scotland in 2012 and 2014. The only Suffolk data comes from Herringfleet by Morley in 1903/ 1904, but there are also several records from the Norfolk Broads, Wicken Fen and the Breckland Meres. Paralona pigra (Sars, 1862) Striped Mud-waterflea Suffolk: No records UK: 218 records Originally Chydorus piger, but updated in the CIG list of 2012, Paralona pigra is most common in the littoral zone of large lakes, though it can also occur in small ponds. There are a great many records from the Lake District, but other English data is widespread and very sparse indeed, although John Hearn found it in Heigham Sound, Norfolk in 1968. Many older records also come from Central Scotland, the Hebrides and Shetland. Phreatalona protzi (Hartwig, 1900) Suffolk: No records UK: 2 records In earlier keys e.g. (Scourfield & Harding, 1966), Phreatalona protzi keys out as Alona protzi. Known only from two literature records extracted by John Bratton from Norfolk, described as ‘Ludham Bridge, River Ant Bridge woodwork’ (Gurney, 1921). Since P. protzi has an unusual ecology of occupying interstitial spaces in the substratum this record implies it was found by digging around the posts supporting the bridge. Pleuroxus aduncus (Jurine, 1820) Pin-tailed Mud-waterflea Suffolk: 8 records UK: 138 records As the common name implies, Pleuroxus aduncus is found amongst the substratum and plants of small ponds or lakes, in situations where plants are few or missing it can be found among dead leaves. The edge of the postabdomen has fine bristles in groups which gave rise to ‘Pin-tailed’ as a descriptive name. All records are from sites south of the Lake District and though traditionally regarded as a species of the south east, from recent data it appears to be widespread in North Wales, the North West of England and Lincolnshire as well as Southern Ireland. In Suffolk it was recently found in ponds in Parham, Raydon and Assington, in lakes at Elveden and archive records exist for Fritton Decoy and Oulton from 1903. Pleuroxus denticulatus Birge, 1879 Suffolk: 4 records UK: 23 records This species has a rather more rounded outline than many Chydorids, with the postabdomen truncated at a sharp angle before the claw and usually with clear diagonal striping. Pleuroxus denticulatus is a littoral species found amongst weeds or debris in ponds and lakes. The distribution is widespread but it is not a common species, so far records have all been south of a line drawn from the Wash to Milford Haven. In Suffolk it has been found in a lake at Elveden, a well vegetated Dyke at Oulton Marshes, Flatford Mill and a restored woodland pond in Raydon. Trans. Suffolk Nat. Soc. 56 (2020)

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Pleuroxus laevis Sars, 1862 Pointed-tail Waterflea Suffolk: No records UK: 34 records The FBA Key (Scourfield & Harding, 1966) states that Pleuroxus laevis is widely distributed, but that obscures how scattered its distribution seems to be. A cluster of sites in the central belt of Scotland, another in the Lake District, a couple in Yorkshire, one on the Welsh border and the only recent record from Anglesey by John Bratton in 2015. Nearer to home it was found twice in the Norfolk Broads in 1898 and at WIcken Fen in 1932. It would be surprising but gratifying to find it in Suffolk.

Pleuroxus truncatus (Müller, 1785) Small Crawling Waterflea Suffolk: 9 records UK: 397 records The FBA Key (Scourfield & Harding, 1966) uses a synonym of Pleuroxus truncata and refers to this cladoceran as Peracantha truncata. It is very easy to identify because unlike any other Chydorid the whole of the free hind margin of the carapace has between 11 and 20 coarse saw like teeth. P. truncata is very widely distributed and common all over the British Isles, in Ireland and all areas of England, Wales and Scotland; including the Western Isles though not as yet from Orkney or Shetland. Not restricted to any particular type of P. truncatus Flatford waterbody it can be found both in aquatic vegetation and on a mud, sand or stony substratum. In Suffolk there are several records from ponds and lakes in the Flatford area, from ponds in Rendlesham Forest, a farm pond in Boxford and from Bixley Decoy Lake. Judging by how common the species is elsewhere Suffolk data so far are surprisingly widespread and somewhat sparse.

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Pleuroxus trigonellus (Müller, 1785) Suffolk: 15 records UK: 194 records Oval in outline with a strongly convex dorsal margin to the carapace, Pleuroxus trigonellus is found in amongst water weeds or on mud in the littoral region of water bodies of all sizes. Found in all regions of the British Isles, even from the more remote Scottish Island groups it is certainly widely distributed and is probably very common, data being limited only by the number of recorders. The earliest local record was by Claude Morley in 1903 at Fritton Decoy, Suffolk sites include farm ponds and a lake near Boxford, lakes at Elveden, Hullbacks Reservoir in Assington, and Cribbensgate Lake at Flatford in 2016. It was even found in samples from the River Gipping at West End Road Ipswich.

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Pleuroxus uncinatus Baird, 1850 Suffolk: 10 records UK: 105 records In many ways Pleuroxus uncinatus resembles P. trigonellus in overall shape and even in many details of the postabdomen, however whereas in P. trigonellus the rostrum points if anything slightly backward towards the body, in P. uncinatus the rostrum curves forward and most often it is upturned curving abruptly outwards at the distal end. It may occur in smallish ponds but has a preference for larger water bodies where it occurs at the bottom. This may be amongst vegetation but is often amongst leaves and other detritus on a muddy, sandy or stony bed. It is widely distributed and though records are most numerous in East Anglia and South East England, scattered records occur in Ireland, Wales and north as far as the Scottish Central Belt. In Suffolk it has been found since 1958 until the present day from large ponds and a lake at Flatford Mill. Other sites are West Stow Country Park, Lound Reservoirs, one lake at Elveden Forest, Lackford Lakes, Holbrook Lake in Boxford, Hullbacks Reservoir in Assington and Framlingham Mere. Pseudochydorus globosus (Baird, 1843) Suffolk: 4 records UK: 127 records As has been described previously both Anchistropus and Pseudochydorus have a peculiar feeding ecology, respectively as carnivores and scavengers. Pseudochydorus, scavenges on carrion (Fryer, 1968). Both genera have a unique limb morphology divergent from other Chydoridae allowing them to feed on soft tissue instead of small particles. Fryer (1968) suggested that Pseudochydorus is an obligate scavenger that cannot be cultured on a diet of detritus and algae. It should be borne in mind that being a scavenger slightly alters the way one needs to search for P. globosus, instead of the trawling for Cladocera with a plankton net through weeds and open water one needs to examine any areas where detritus including carrion may be found. Originally described from the United Kingdom as from “Ditch near Richmond; pond near Isleworth” in Baird (1835). Most of the UK data are archive records, that is pre 1966, and only 4 were made in the last 20 years. In Suffolk P. globosus was taken in 1993 in a Boxford lake, in 1998 at West End Road, Ipswich and twice in 2009 in lakes at Elveden. Rhynchotalona falcata (Sars, 1862) Long Nosed Waterflea Suffolk: No records UK: 97 records Rhynchotalona falcata has 7 setae on the antenna and in this resembles Disparalona rostrata which in older keys (e.g. Scourfield & Harding, 1966) was also put into the genus Rhynchotalona. However, the rostrum of R. falcata is very long and curves back to almost touch the ventral carapace, bending much further than that in D. rostrata. It inhabits the bottom sometimes within vegetation but is found most often on bare stones or sand. Whilst it is found in all sizes of waterbody the records in the CIG database are predominantly from lakes, reservoirs and larger waters. There are a few scattered archive records from the south of England but most data, especially recent records, are from the West in Ireland, Wales, the Lake District and Scotland, including the more remote islands. Trans. Suffolk Nat. Soc. 56 (2020)

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Tretocephala ambigua (Lilljeborg, 1900) Suffolk: 1 record UK: 4 records The FBA Key (Scourfield & Harding, 1966) using a synonym of Tretocephala ambigua refers to this cladoceran as Alonopsis ambigua. The species is broadly similar to A. elongata, but in this case is very rare indeed occurring nowhere but Norfolk and possibly Suffolk. It is worth repeating here that A. elongata is unknown from South East England. The NBN Atlas lists 11 records for T. ambigua in the British Isles, but careful examination shows that these are in fact only the 4 distinct records in the CIG database, each of which has been sent up 2 or 3 times from different organisations (CIG, SBIS & NBIS). The first mention of this species occurs in Scourfield & Harding (1966) as being rare, but present in Norfolk with the reference (Gurney, 1905). It seems certain this refers to a 2-page entry in the Transactions of the Norfolk Naturalists’ Society reporting a record from 1904 by Claude Morley. This is also reported in the transactions of the Suffolk Naturalists’ Society and given as Herringfleet but could have been either side of the county border, presuming Morley walked up from Somerleyton Station! A second puzzling record is that Scourfield himself seems to have gone looking for it. John Hearn ran a Cladocera recording scheme through the 1970s and 80s and according to John Hearn’s database Scourfield found A. ambigua on 14/07/1919 at TG4421. From the OS map this is in the vicinity of Meadow Dyke / Blackfleet Broad, but John Hearn listed this as “Hickling Broad, Miss Turner’s Island”. Since then it has only been located in 1971 at 3 sites by Raymond Watson in his M.Phil. Thesis, all from Breckland Meres in Norfolk. In the thesis he gives the following details, taken from notes made from a borrowed copy. “Tretocephala ambigua was a rare species in Breckland meres, being rarely found in the water though ephippia were often found in mud.” Ophryoxidae Ophryoxus gracilis Sars, 1861 Pointed-shell Waterflea Suffolk: No records UK: 5 records In many keys Ophryoxus gracilis is placed in the family Macrothricidae, which it closely resembles due to the elongated, slender antennule; and yet the short rostrum and shell spine reminds one of Daphnia. A distinctive shape unlike any other cladoceran. Ophryoxus gracilis is a totally northern species, existing scarcely anywhere outside of Scandinavia. In Britain it has been found in only two sites, Loch Ness and nearby Loch Ruthven, it was last recorded in 1984. Acantholeberidae Acantholeberis curvirostris (Müller, 1776) The Moor or Marsh Waterflea Suffolk: No records UK: 51 records Acantholeberis curvirostris used to be listed amongst the family Macrothricidae. It has a very distinctive appearance with a large head and long curved antennae very different from other Cladocera. It prefers acid waters often with a pH<5 or else in occasional small ponds and lakes often with a high content of humus. Although not

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recorded in Suffolk there are two records on the NBN Atlas from West Norfolk, many of the other records come from Wales and Scotland. That there are only 51 records across the UK testifies to its rarity. Macrothricidae Drepanothrix dentata (Euren, 1861) Toothed-back Waterflea Suffolk: No records UK: 109 records This rather strange looking species is easily recognized by the large tooth in the middle of its arched dorsal shell. Like all the Macrothricidae it has a very long, moveable antennule, reminiscent of an elephant’s trunk! Living in the littoral zone among weeds in pools and the swampy margins of lakes it is not common. Records for this species show a scattered and widespread distribution along the south coast from Hampshire to Cornwall, through West Wales, the Lake District, Scotland and the islands including Shetland. It has never been recorded from the East of England. Lathonura rectirostris (Müller, 1785) Suffolk: 2 records UK: 42 records Resembling D. dentata, but with a more oval carapace and lacking the tooth on the dorsal edge, Lathonura rectirostris has a slenderer, tapering antennule. In colour it is tinted red or yellow and is found amongst weeds in ditches, ponds and lake shores. The majority of records on the CIG database were made between 1896 and 1930 from the South Coast, Suffolk, Norfolk, Cambridgeshire, Wales and the North West with a few from Ireland, the Lakes and Scotland. More recent records have been made from old sites in Anglesey and in 1979 by Raymond Watson from the Breckland Meres where he noted that L. rectirostris was hatched from the wet mud of the Bagmore Pit, although ephippia were not found or specifically reared. The two Suffolk records were from Hopton Fen and Hopton Bridge in 1911 by D. J. Scourfield, where perhaps mud samples would prove worth collecting. Macrothrix hirsuticornis Norman & Brady, 1867 Smooth Mud Waterflea Suffolk: No records UK: 28 records In both the next two Macrothrix species the ‘elephant trunk’ like antennule becomes wider at the tip and both are also bottom dwelling, either close to bare mud or sand or amongst vegetation, so trawling with a plankton net is less likely to turn them up. M. hirsuticornis has a smooth dorsal edge to the carapace and is a relatively rare inhabitant of pools, ponds and lakes but is also likely to turn up in unexpected places; a few recent records being from flooded wheel ruts on farms, hollows on a footpath and scrapes at Slimbridge! There are many older records from Sussex, Essex and Norfolk, and a few modern ones from north Wales especially Anglesey, Lincolnshire & the tip of Scotland. Macrothrix laticornis (Jurine, 1820) Saw-backed Mud Waterflea Suffolk: 3 records UK: 58 records With the same broad tip to the antennule but differing from M. hirsuticornis because of the finely serrated dorsal edge of the carapace or shell, Macrothrix laticornis is

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found in very similar habitats. It is also relatively rarely recorded. In fact there are many older records but fewer modern ones for this species. Its distribution seems broadly similar M. hirsuticornis above with the exception of any Scottish data. In Suffolk Morley found it at Lound in 1903, the other two records are from Flatford in the 1970s and were copied from the old card index at the FSC study Centre at Flatford Mill. Macrothrix rosea (Jurine, 1820) Suffolk: 1 record UK: 3 records In older keys Macrothrix rosea will key out as Echinisca tenuicornis; both E. rosea and E. tenuicornis being synonyms of M. rosea. A mud dweller its head has arched ridges and it possesses a slender antennule, not broader at the tip, which sets it apart from our other Macrothrix species. All of these mud water fleas are rare but M. rosea is by far the rarest. The NBN Atlas contains a single unattributed record from Larling Heath, North East of Thetford, sent in by English Nature and dated 1927. However the CIG database has three records, two of which are very relevant to us in Suffolk. The oldest record of the species was from Lochmaben Loch in Dumfries in 1840 by none other than William Baird the Victorian zoologist, an important figure in the early study of cladocera. No further records of this species were then made until 1972 when Raymond Watson, researching for his M.Phil. Thesis from the UEA rediscovered it. Some years ago Raymond lent me his thesis to read and from the notes I made at the time it is clear that his is the record on the NBN Atlas from Larling Heath, although no name is given and the date is mistyped. Raymond’s thesis shows he hatched M. rosea from mud collected at Langmere & the mere on Larling Heath, both of which are Breckland sites just over the border in Norfolk. He commented further that “Large numbers of Ephippia were found at Larling Heath” and “The ephippium contains two eggs and is usually yellow or orange- brown” The thesis also contains reference to scanning electron micrographs he took of the ephippia at the time describing the unusual surface sculpturing as having “A mosaic of flat topped projections.” Streblocerus serricaudatus (Fischer, 1849) Hump-backed Waterflea Suffolk: No records UK: 40 records Streblocerus serricaudatus has a humped edge to the carapace and a very distinctive postabdomen. It is found in bogs, swamps and pools in the vegetation especially where there is sphagnum. In common with certain other cladocerans, especially Chydoridae sphaericus, one method of collecting is to squeeze clumps of wet sphagnum into a fine net. All records are from the Western side of the British Isles, one from a bog in West Ireland, some from West Wales, the Lake District, a couple from the Scottish mainland and several from Rhum in the 1970s. Polyphemidae Polyphemus pediculus Linnaeus, 1761 Predatory Giant Eyed Waterflea Suffolk: 8 records UK: 354 records Like its namesake in Greek mythology Polyphemus pediculus has a large single eye taking up most of the head, and like Bythotrephes longimanus is an active predator of

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other zooplankton. It has a relatively small carapace which merely covers the brood chamber and not the postabdomen nor legs. Despite only having a single eye P. pediculus can actively chase down its prey by using visual cues (Young & Taylor, 1988). These enable it to choose suitable sized prey, it cannot consume too large or too small crustaceans. It is also able to judge when it is near enough to accelerate and pounce. Once it has grabbed another crustacean in its legs it basically moves it against the mouth and literally grinds it away with teeth on the mandibles, P. pediculus with several young in the finally pushing the parts into its food brood pouch, grasping arms outside the chamber (Butorina & Sorokin, 1965). carapace and single large predatory eye. This species is widely distributed across the British Isles but does seem more common in some areas than others, with more records from East Anglia and the South East, from North Wales, the Lake District and Scotland; apparently more occasional elsewhere. It is found in canals, large dykes and lakes and does seem more common in larger water bodies. It can form large ‘shoals’ in the littoral zone and can be very conspicuous especially as it can have bright blue or red colour patches on the body caused by chromatophores which develop with age. In Suffolk it has been found at Lound Reservoirs, Dykes at Oulton and Carlton Marshes and several times at Flatford Mill, all are recent records and were made between 2006 and 2015. Cercopagidae Bythotrephes longimanus Leydig, 1860 Long-tailed or Spiny Waterflea Suffolk: No records UK: 16 records Bythotrephes longimanus is an almost transparent waterflea and is instantly recognizable by its long caudal process or tail, which can reach 10 mm or more. Defensive spines on this tail gave rise to the common name. It also has a bulging brood chamber with eggs or embryos on the dorsal side. Very different from other cladocerans this predatory species has, like Polyphemus pediculus, a single very large eye taking up most of its head with which it hunts down other zooplankton. It migrates into deeper waters during the day, hiding from predators, returning to shallower water at night to find food. Accidentally introduced by the discharge of contaminated ballast water into the Great Lakes from cargo ships in 1982 it has become an invasive pest in the USA. In the UK it exists as a native limnetic predatory species of large lakes and reservoirs in Wales, the Lake District and Scotland.

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Acknowledgements Firstly, I must thank the many members of the Cladocera Interest Group who have provided much of the data and background knowledge presented here. My thanks also to Helen Roy and Stephanie Rorke of the National Biodiversity Network who made available and allowed the data from the two early Cladocera recording schemes run by David Scourfield and John Hearn. Finally to thank Raymond Watson for loan of his thesis several years ago, from which notes were made about important species from the Breckland meres. The Cladocera Interest Group website: www.cladocera.org.uk References Alvarez, S. & Fletcher, M. (2016). Hidden for 60 years...cryptic species sees the light of day at last. Cladoceran News, 8, Winter p20. www.cladocera.org.uk. Amoros, C. (1984). Crustacés cladocères. Monthly Bulletin of the Société Linnéenne de Lyon Tome 53 n°3-4. (Downloadable from: http://www.microscopy-uk.org.uk/ mag/cladocera-key/Cladocera-key-v1.pdf ). Baird, W. (1835). The natural history of the British Entomostraca. Ann. Mag. Nat. Hist., 11: 81-95. Bratton, J. (2011). Dunvhedia crassa in the British Isles. Cladoceran News, 2, Winter p5. www.cladocera.org.uk. Bratton, J. (2013). A summary of Eurycercus glacialis in Scotland. Cladoceran News, 4, Summer p2. www.cladocera.org.uk. Bratton, J. (2014). That Scottish Chydorus gibbus record: more details. Cladoceran News, 5, Spring p10. www.cladocera.org.uk. Brooks, J. L. (1957). The systematics of the North American Daphnia. Mem. Conn. Acad. Arts. Sci. 13, 1-180. Butorina, L. G., & Sorokin, Yu.I. (1965). On the nutrition of Polyphemus pediculus. Trudy Inst. Biol. Vnutr. Vod. 12(15), 170-174. Chalkley, A. (2011). Notes to the Revised British species list for the Branchiopoda: Cladocera & Branchiopoda: Leptodorida. Cladocera Interest Group Website. Downloaded October 2020. www.cladocera.org.uk. Dumont, H.J. & Negrea, S.V. (2002). Branchiopoda. Guides to the Identification of the Microinvertebrates of the Continental Waters of the World. Volume 19. Backhuys Publishers, Leiden. Fryer, G. (1968). Evolution and adaptive radiation in the Chydoridae (Crustacea: Cladocera): a study in comparative functional morphology and ecology. Philos. T. Roy. Soc. B, 254: 221-285. Fryer, G. (1993). The Freshwater Cladocera of Yorkshire. A Faunistic and Ecological Survey. Yorkshire Naturalists Union, Wilson & Son, Kendal. Green, J. (2012). Daphnia parvula, a new record with notes on identification. Cladoceran News, 3, Winter p10. www.cladocera.org.uk. Gurney, R. (1921). Two new British Entomostraca: Alona protzi, Hartwig, and a new species of Mesochra in Norfolk. Annals and Magazine of Natural History, series 9, 7: 236-.

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Trans. Suffolk Nat. Soc. 56 (2020)