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Classification of Echinoderms. Taxonomists divide the 7,000 species of echinoderms into six classes, five of which we will discuss. Class Crinoidea. Called crinoids, include the sea lilies and feather stars. The name crinoid means “lily-like.” About 600 living species.
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Classification of Echinoderms Taxonomists divide the 7,000 species of echinoderms into six classes, five of which we will discuss
Class Crinoidea • Called crinoids, include the sea lilies and feather stars. • The name crinoidmeans “lily-like.” • About 600 living species. • Sea lilies most closely resemble the fossils of ancestral echinoderms from the Cambrian period. They are sessile as adults, remaining attached to rocks or the sea bottom. Sessile Free-moving
Class Crinoidea • Feather stars, in contrast, can swim or crawl as adults, although they may stay in one place for long periods. • In both types of crinoids, five arms extend from the body and branch to form many more arms – up to 200 in some feather star species. Fossil specimen of stalked sea lily
Class Crinoidea • Sticky tube feet located at the end of each arm filter small organisms from the water. The tube feet also serve as a respiration surface across which crinoids exchange oxygen and carbon dioxide with the water. • Cilia on the arms transport trapped food to the crinoid’s mouth at the base of the arms. The mouth faces up in crinoids, while in most other echinoderms the mouth faces toward the sea bottom.
Class Ophiuroidea • Consists of basket stars and brittle stars. • Distinguished by their long narrow arms, which allow them to move more quickly than other echinoderms. • About 2,000 species – the largest echinoderm class. Basket stars Brittle star
Class Ophiuroidea • Brittle stars, so named because the coiled branches of their flexible arms break off easily, can regenerate missing parts • Most basket stars and brittle stars are active at night and are usually found beneath stones or seaweed or buried under the sand.
Class Echinoidea • Consists of about 900 species of sea urchins and sand dollars. • Echinoideameans “spinelike” • Sea urchins are well adapted to live on hard sea bottoms. They use their tube feet for locomotion and feed by scraping algae from hard surfaces with the five teeth that surround their mouth. Underside of urchin showing teeth
Class Echinoidea • In some sea urchins, the spines are flexible, while in others, they are hollow and contain a venom that is dangerous to predators as well as swimmers. Pencil Sea Urchin (flexible spines) Purple Urchin
Class Echinoidea • Sand dollars live along seacoasts. They are usually found in coastal areas and have the flat, round shape of a silver dollar. Their shape is an adaptation for shallow burrowing. The short spines on a sand dollar are used in locomotion and burrowing, and they help clean the surface of the body. They use their tube feet to capture food that settles on or passes over their body.
Class Holothuroidea • Sea cucumbers belong to the class Holothuroidea • Armless. Live on the sea bottom, where they crawl or burrow into soft sediment • About 1,500 species • The ossicles that make up their endoskeleton are very small and are not connected to each other, so their bodies are soft.
Class Holothuroidea • Modified tube feet form a fringe of tentacles around the mouth. When these tentacles are extended, they resemble the polyp form of some cnidarians. That explains the name of this class, which means “water polyp.” • A sea cucumber uses it tentacles to sweep up sediment and water. It then stuffs its tentacles into its mouth and scrapes the food off them. • Unique defensive behavior: Can forcefully eject part of their internal organs when threatened.
Class Asteroidea • The sea stars belong to the class Asteroidea, which means “starlike” • About 1,500 species • They live in coastal waters all over the world • They exist in a variety of colors and shapes and can have dozens of arms • They are economically important because they prey on oysters.
