What are Echinoderms?
Among the echinoderms there are feathers and lilies, stars and cucumbers, urchins and dollars. This strange assortment is grouped together in an animal phylum, for all of the strange echinoderms are animals. They were most likely named lilies and cucumbers, stars and feathers before people realized that they were really animals.
We know of at least 5,000 different varieties and all of them live in the salty sea. They belong to the animal phylum Echinodermata, which means the spiny skinned animals. From their scientific name, we would expect them to be covered with prickles, perhaps like porcupines. But only a few of the echinoderms are armed with spears.
The echinoderms are simple fellows without heads, though each has a mouth and a stomach for digesting all manner of sea food. Each has gills for taking oxygen from the water and most echinoderms are just a few inches long. Though not all enchinoderms have prickles, they all have one most amazing feature in common.
The animals in our everyday world are two sided, left and right. We are so used to this two sided plan that it is hard to imagine a body wl$1h is not two sided, left and right. But the echinoderms defy this rule. Every last one of them has a body built on five sided plan.
By now you have guessed that the echinoderm we are most likely to see is the starfish. His five sided body plan is very obvious in his five little tapering arms. However, he has starfish cousins in which the five sided plan is not so obvious. Some have ten arms, some have twenty arms and some have no space between their arms and look like flat saucers.
The phylum Echinodermata is subdivided into five classes, In one class we have the many varieties of starfish, In another class we have the sea urchins and the sand dollars, These fellows are armed with prickles and the sea urchin. looks like a well filled pincushion.
In another class of echinoderms we have the brittle star3 which resemble long legged starfish and walk on tiptoes over the floor of the sea. In another class we have the dainty feather stars and sea lilies and there is a class of echinoderms which includes a variety of chubby sea cucumbers.
The starfish is a common sight in tidal pools and we often find the bony remains of the sand dollar on the beach. We see the prickly sea urchin, burying himself in the sand less rarely. Feather stars, sea lilies and sea cucumbers live in deep water and as a rule we see them only when stormy seas wash them high and dry onto the beaches.