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Starfish
Looking very stylish in his beach shorts and sun hat, our vet Joe Inglis is off to the seaside to see what he can learn about these weird and wonderfully pointy animals.
Starfish are marine invertebrates (which means they don’t have bones supporting their bodies). They live on the seabed of every ocean around the world, from the frozen depths of the Arctic and Antarctica to the warm waters of the tropics. They have super-tough skin with scales or spines to protect them from predators.
Super symmetry With five or more arms radiating out from a central disc, starfish look very different from most animals as they can’t be divided neatly into left and right sides. Instead, starfish show what’s called radial symmetry, which means they look the same on either side of lots of different lines drawn through their central discs.
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The number of arms that a species of starfish found in the Antarctic can have. That’s a lot of gloves to find when it gets really cold!
© Anna Komeleva / Shutterstock.com
Water-powered Unlike vertebrate animals that use muscles and bones to move their bodies around, starfish use water power! They squeeze sacs called ampullae which push seawater through canals in their arms and into their sticky tube feet underneath. This hydraulic power allows them to move their arms and grab things with their feet – but it’s not very fast. Most starfish can only move around 15 cm per minute, which means a 100-metre sprint would take them over 11 hours!
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