Echinoderms are very common and diverse in the oceans of the past and present, and are an important part of the marine communities they inhabit. The first accepted Echinoderm is from the Early Cambrian Period. The defining characters of Echinoderms are the normally five sided radial symmetry, interlocking calcium carbonate plates covered by a spiny leathery skin, a water vascular system and tube feet for capturing food, respiration, and/or locomotion. Echinoderms are very complex invertebrates, many are composed of hundreds of calcareous skeletal parts or plates, and even though they are common in Paleozoic marine communities they are rarely preserved complete. They fall apart quickly after death and their many plates scattered by the ocean currents and scavengers. The calcium carbonate plates are not solid but are a spongy looking microcrystalline structure that is distinctive to the phylum. The plates are connected by ligaments primarily composed of collagen, some plates are closely joined with little movement, like in the body and some are articulated plates that move more freely. This is achieved through certain ligaments that are variable and a new position is achieved without the use of muscular tissue.

There are five classes of Echinoderm living in the oceans today and many extinct classes. The different classes exhibit great variation in body structure and approach to life. Echinoderms have left a very good fossil record and the list below is the Classes of Echinoderms you may find in the North Alabama and Tennessee Valley area.