Class Asteroidea

Although often called 'starfish,' these animals are echinoderms ('spiny skins'), not fish. Sea stars have an eyespot on the tip of each 'arm,' or ray, capable of sensing light and dark. They move by a unique hydraulic mechanism: water flows through the sieve plate on top of their central disc and through passageways that end in hundreds of tube feet, each of which is tipped with a tiny suction cup. Sea stars also use this precision system of locomotion to support their predatory lifestyle. When eating a bivalve, a sea star places its mouth on the seam between the halves of the shell, then uses its tube feet to force the shell apart until it is able to expel its stomach through the gap. Sea stars then digest the hapless creature within its own shell.

Sea stars are such voracious hunters they have been known to decimate beds of oysters, scallops, and other shellfish overnight. Fishermen who tried to protect their livelihood by cutting the sea stars in pieces and throwing them back in the water found out the hard way that they could regenerate themselves from any ray that contained a piece of the central disc -- instead of reducing the competition, they were actually making things worse!

Cool Links:

Starfish Science - A friendly and accurate starfish FAQ with photos and illustrations.

Larvae of a Starfish - photo of the microscopic larvae of the sea star Asterias rubens, with links to other nifty photo pages.

Echinodermata Reference & Virtual Dissections - from the School of Biological Sciences, University of Sydney. Requires the free Authorware Player from Macromedia.

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