Nonvertebrate Chordates, Fishes, and Amphibians Biology II: Chapter 30
CHORDATES
Chordates • Phylum Chordata • Fishes, amphibians, reptiles, birds and mammals • Four key characteristics: 1. Dorsal, hollow nerve cord 2. A notochord 3. Pharyngeal pouches 4. Tail that extends beyond the anus
Dorsal, Hollow Nerve Cord • Nerves branch from this cord at regular intervals • Nerves connect to internal organs, muscles and sense organs
Notochord • Long support rod • Runs through the body just below the nerve cord • Most chordates only have in the embryonic stage
Pharyngeal Pouches • Paired structures in the throat (pharynx) region • Fishes and amphibians: slits develop that connect the pharyngeal pouches to the outside of the body • The slits may then develop into gills that are used for gas exchange
Tail • All chordates have a tail that extends beyond the anus at some point in their lives • The tail can contain bone and muscles and is used in swimming by many aquatic species
Most Chordates are Vertebrates • More than 99% of all chordates are in the subphylum Vertebrata • Vertebrae: individual segments that make up the backbone; encloses and protects the spinal cord • Backbone is part of an endoskeleton, or internal skeleton
Nonvertebrate Chordates • The two groups • Softbodied marine organisms • Have the four key characteristics at some point in their lives • Tunicates – Filter feeders
• Lancelets – Small, fishlike creatures
Fishes • Aquatic vertebrates that are characterized by: • Paired fins – Used for movement
• Scales – Used for protection
• Gills – Used for exchanging gases
Evolution of Fishes • Fishes were the first vertebrates to evolve • The evolution of jaws and the evolution of paired fins were important developments during the rise of fishes
The First Fishes • Jawless creatures whose bodies where armored with bony plates • Lived in the oceans during the late Cambrian Period, about 510 mya • Fishes kept this armored, jawless body plan for 100 million years
The Age of Fishes • Ordovician and Silurian Periods: 505410 mya, fishes underwent a major adaptive radiation • Devonian Period: “Age of Fishes” • Some were jawless with little armor • Ancestors of modern hagfishes and lampreys • Others were armored and ultimately became extinct about 360 mya
The Arrival of Jaws • Other ancient fishes kept their bony armor and possessed a feeding adaptation that would revolutionize vertebrate evolution: JAWS • Jawless fishes
– Limited to eating small particles of food that they filter out of the water or suck up like a vacuum cleaner
• Jaws can hold teeth and muscles – Much wider variety of food – Defend themselves by biting
The Arrival of Paired Fins • More control of body movement • Fin tails and powerful muscles gave greater thrust when swimming • Enabled fishes to move in new and varied patterns • This enabled fishes to use their jaws in complex ways
The Rise of Modern Fishes • Although the early jawed fishes soon disappeared, they left behind two major groups that continued to evolve and still survive today – Ancestors of modern sharks and rays: skeletons made of resilient cartilage – Group that evolved skeletons made of true bone
Form and Function in Fishes • Adaptations to aquatic life include: – Various modes of feeding – Specialized structures for gas exchange – Paired fins for locomotion
Feeding • Herbivores, carnivores, parasites, filter feeders, detritus feeders • A single fish may exhibit several modes of feeding (carp: eat what is available) while others are very specialized (barracuda: carnivore) • Pyloric ceca: fingerlike pouches found in many species of fish that secrete digestive enzymes to help digest food
Respiration • Most fishes exchange gases using gills located on either side of the pharynx • The gills are made up of feathery filaments • Lampreys and sharks have several gill openings on the side of the body • A number of fishes, such as the lungfish, have an adaptation that allows them to survive in oxygenpoor water or in areas where bodies of water often dry up
Respiration
Circulation • Closed circulatory systems with a heart that pumps blood around the body in a single loop • Heart consists of 4 parts: – Sinus venosus: thinwalled sac that collects blood from the fish’s veins – Atrium: a large muscular chamber that serves as a oneway compartment for blood – Ventricle: thickwalled muscular chamber; pumping portion of the heart – Bulbus arteriosus: connects to a large blood vessel called the aorta, which moves blood to the fish’s gills
Circulation
Excretion • Most fishes rid themselves of nitrogenous wastes in the form of ammonia • Gills, kidneys – Saltwater fishes • Lose water by osmosis: kidneys return as much water to the body as possible – Freshwater fishes • Gain water by osmosis: kidneys pump out plenty of dilute urine
Response • Welldeveloped nervous systems organized around a brain • Cerebrum: area of the brain responsible for all voluntary activities of the body • Cerebellum: region of the brain that coordinates body movements • Medulla oblongata: area of the brain that controls the functioning of many internal organs
Response • Lateral line system: sensitive receptor system that enables fish to detect gentle currents and vibrations in the water (the 6th sense)
Movement • Most move by alternately contracting paired sets of muscles on either side of the backbone • Because their body tissues are more dense than the water they swim in, sinking is an for fishes
issue
• Swim bladder: gasfilled organ found in many bony fishes that adjusts their buoyancy
Reproduction • Oviparous: term used to refer to animals whose eggs hatch outside the mother’s body • Ovoviviparous: term used to refer to animals whose young are born alive after developing in eggs inside the mother’s body • Viviparous: term used to refer to animals that bear live young that are nourished directly by the mother’s body as they develop
Groups of Fishes • Over 24,000 living species that are extremely diverse • Jawless fishes • Cartilaginous fishes • Bony fishes
Jawless Fishes • Have no true teeth or jaws • Skeletons are made of fibers and cartilage • Lack vertebrae; keep notochords as adults • Two main classes: – Lamprey – Hagfishes
Sharks and Their Relatives • Class Chondrichthyes • Sharks, rays, skates, • Also: sawfishes and chimaeras • Cartilage, not bone
350 Living Species • Curved tails • Torpedoshaped bodies • Pointed snouts • Mouth underneath • Enormous number of teeth • Always exceptions!
Bony Fishes • Class Osteichthyes • Skeletons made of hard, calcified tissue: bone • Rayfinned fishes – Rays or spines that support the fins – Only 7 living species of bony fish are not rayfinned
• Lobefinned fishes
Ecology of Fishes • Anadromous: fishes that spend most of their lives in the ocean but migrate to fresh water to breed – Examples: lampreys, sturgeons, and salmon
• Catadromous: fishes that spend most of their lives in fresh water but migrate to the ocean to breed – Example: European eel, American eel
AMPHIBIANS
Amphibian • Have survived for hundreds of millions of years • The only modern of an that other
descendants ancient group gave rise to all land vertebrates
• Amphibian means “double life”…live in both water and on land
Amphibian • Vertebrate • Lives in the water as a larva and on land as an adult (with some exceptions) • Breathes with lungs as an adult • Has moist skin that contains mucus glands • Lacks scales and claws
Evolution of Amphibians • The first amphibians to climb onto land probably resembled lobefinned fishes similar to the modern coelacanth • The amphibian had legs, appearing about 360 mya
Evolution of Amphibians • Early amphibians evolved several adaptations that helped them live at least part of their lives out of water: – Bones in the limbs and limb girdles became stronger for more efficient movement – Lungs and breathing tubes enabled them to breathe air – The sternum formed a bony shield to support and protect internal organs, esp. the lungs
Evolution of Amphibians • Soon after they appeared, amphibians underwent a major adaptive radiation • Some were huge: Eogyrinus was about 5 meters long! • Amphibians became the dominant form of animal life in the warm, swampy fern forests about 360286 mya • Climate changes caused many of the swamps to disappear • Most amphibians became extinct
Evolution of Amphibians • Only three orders of small amphibians survive today: • Frogs and toads • Salamanders • Caecilians
Form and Function in Amphibians • Although the class Amphibia is relatively small, it is diverse enough to make it difficult to identify a typical species • We will focus on the structures found in frogs…
Feeding • Tadpoles – Filter feeders or herbivores that graze on algae – Eat almost constantly
• Adult amphibians – Almost entirely carnivorous
• Mouth esophagus stomach small intestines large intestines cloaca
Respiration • Larval amphibians – Gas is exchanged through the skin and gills
• Adult amphibians – Lungs and skin
Circulation • Double loop • 3 chambered heart First Loop • Carries oxygenpoor blood: heart lungs and skin • Takes oxygenrich blood: lungs and skin heart
Circulation Second Loop • Transports oxygenrich blood: heart rest of the body • Transports oxygen poor blood: body heart
Circulation
Excretion • Amphibians have kidneys that filter wastes from the blood • Urine: The excretory product of the kidneys • Urine travels through tubes called ureters into the cloaca • Urine is passes outside or temporarily stored in a bladder above the cloaca
Reproduction • Eggs do not have shells and tend to dry out if they are not kept moist • Most species lay eggs in the water • The male fertilizes them externally • In a few species (most salamander), eggs are fertilized internally
Reproduction • The male climbs onto the female’s back • The female releases the eggs that are then fertilized • The eggs are in a transparent jelly, useful for attaching the eggs to underwater plants and that provides nourishment to the growing cells
Reproduction • Some amphibians abandon their eggs after they are laid • Others incubate the young in their mouth, on their back, or even in their stomach!
Movement • Amphibian larvae – Often move very much like fishes, wiggling their bodies and using a flattened tail for propulsion
Movement • Adult amphibians – Most use their front and back legs to move in a variety of ways – Jump, climb, run, etc.
Response Nictitating Membrane: • Moveable transparent membrane in amphibians located inside the regular eyelid • Protects the surface of the eye from damage under water and keeps it moist on land
Response Tympanic Membrane • Eardrum of amphibians • Inside the skull • Vibrates in response to sound, allowing hearing
Groups of Amphibians • Salamanders: Order Urodela – Long bodies and tails – Four legs – Carnivores
• Caecilians: Order Apoda
• Frogs and Toads: Order Anura – Frogs: Long legs and lengthy jumpers – Toads: short legs and short hops – Adults lack tails
– Legless animals that live in water or burrow in moist soil or sediment
Ecology of Amphibians • Have no feathers, fur or scales • Many are ideal for predators such as birds and mammals
Ecology of Amphibians • Amphibians have adaptations to protect themselves • Many have skin colors and markers that allow them to blend in with the environment • Some release toxins • Some are brightly colored as a warning to predators