On a recent trip to the Crocker Neck Salt Marsh in Cotuit, my students discovered an unusual looking animal in the wrack line. It turned out to be a hairy sea cucumber (Sclerodactyla briareus), a species belonging to the group echinoderms which also includes sea stars and sand dollars.
These interesting animals are slow moving critters which live on or near the ocean substrate. They have a thick skin covered with small tube feet that enable them to crawl slowly on the ocean floor. They feed on small bits of food such as algae, and are dark in color. If disturbed these animals exhibit a unique method of protection. They will discharge some of their internal organs. Like other echinoderms they can quickly regenerate these lost structures.
The Echinodermata is a unique group of animals found exclusively in the marine environment. They all possess an endoskeleton and move with tube feet that grip the surface like tiny suction cups. The sea stars are characterized by an elaborate series of internal canals for the movement of water called a water vascular system. Another interesting feature of this group is that they are an important part of the zooplankton, though their larval stages donít resemble the adults at all.
Sea urchins belong to this group also, and have their own set of unique features. For example, these animals like to graze mainly on large algae, such as kelp, and use a chewing structure called Aristotleís lantern. Even though the purple (Arbacia punctulata) and green (Strongylocentrotus droebachiensis) urchin species on Cape Cod are covered with spines, they are harmless to people. Sometimes you find their spineless shells on the beach after they die.
Of course the sea stars or starfish are the most frequently seen, usually in tide pools or protected in the crevices of rock jetties. Sea stars love to feed on bivalve mollusks, particularly mussels. Their arms attach to the mussel, pry it open, and slide their stomach inside the clam to digest it. Occasionally you will find a sea star that is missing one of its five arms, or you will notice one with a stubby arm. These animals have a strong ability to regenerate any lost limbs. It may take up to a year, but the animal has no problem surviving as it regenerates.
In spite of their evolutionary longevity and strong adaptive features, echinoderms are also adversely impacted by environmental contamination. Global warming has resulted in the acidification of seawater, reducing the calcification process essential to these animals. And any changes in their benthic habitats from bottom trawling to oil spills can also reduce their populations.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.