Some Odd Bods

Forest and Bird, Issue 302, 1 November 2001, Page 35

Some Odd Bods

There seems no limit to the oddities of the echinoderms. Their skeletons are made, not of bone or cartilage or chitin, but of calcareous fragments called ossicles. These fit together like a mosaic in the sea urchins. Many echinoderms are armoured with moveable spines and bumps like speed humps. They move, not through muscle-braced-on-bone but by hydraulics, their spaghetti-like tube feet extending and contracting by water pressure. Echinoderm eating habits are remarkably diverse — and even gross. Sea lilies and feather stars trap minute food in their feathery arms. Sea urchins and sand dollars grind their food with five hard teeth in a device called an Aristotle's lantern. Starfish and some brittle stars are predators. With the suckers of its hundreds of tube feet, a starfish will fix its opposing arms to the shells of a cockle, and pull — and pull — and pull. Eventually the cockle’s muscles tire and it gapes open a little. Through the gap, the starfish pushes Its stomach like a plastic bag, dissolves the flesh of the helpless shellfish and sucks in the soup. Bereft of table manners, the sausage-like sea cucumbers lie on their sides, stuffing into their mouths debris trapped on their sticky tentacles. Upset a sea cucumber and it will throw out all its digestive system — a messy trick which deters even ardent naturalists!