STARFISH

Starfish are members of a very broad and diverse clan - the Echinoderms, a term which translates as spiny skin. There are sea stars, brittle stars, sea cucumbers and urchins. In fact, 6,500 species lurk on the branches of this unusual family tree.

What links them all together is their five-point radial symmetry. Their bodies actually consist of five equal segments, each containing duplicate sets of internal organs, all radiating from a central body mass. This is fairly obvious in a starfish, less so in their relatives. They have no heart, brain or eyes, but some seem to have light sensitive parts on their arms. Mostly their mouth is situated on their underside and their anus on top.

Starfish motion is slower than the proverbial tortoise. They use a complex hydraulic system to move around or cling to rocks. On their base side a mass of tiny tubes run along a distinctive groove in each arm. At the tip of each is a diminutive suction pad - or foot - which is hydraulically controlled by a remarkable system where water is sucked in through a sieve plate on top of their body, then pulsed through interconnecting canals to the toes. Most incredible is their defence mechanism - the capability to regenerate. Should they lose an arm (or is it a leg) to a predator, then no problem! They just grow another. Or if an arm gets misplaced, it can regenerate itself into a whole new creature.

The best known predator in this group is of course, the much-maligned crown-of-thorns starfish. This rather bewitching creature is best known for being able to wipe out whole colonies of hard coral. They feed on corals polyps by sliding that stomach out and suffocating a whole colony beneath, leaving behind just a bleached skeleton. Distant cousins of the starfish are the shy, often hidden, brittle and basket stars.

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