Echinoderms are a phylum of marine animals. The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates. This phylum has five subphylums including:
1. Homalozoa
2. Crinozoa
3. Asterozoa
4. Echinozoa
5. Blastozoa
1. Homalozoa
2. Crinozoa
3. Asterozoa
4. Echinozoa
5. Blastozoa
Dermasterias imbricata (Leather Sea Star)
The mouth of the leather sea star is found on the under side of the sea star. Food enters the mouth and into the first stomach. Then it is passed onto the secondary stomach and then into the many digestive glands that are located within each of the arms of the sea star. These digestive glands secrete enzymes and absorb the needed nutrients from food. A small intestine runs from the secondary stomach to the external port (where the sea star disposes waste), which is located in the central upper part of the body.
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Holothuria floridana (Florida sea cucumber)
The Florida sea cucumber is a scavenger that feeds on debris in the benthic zone of the ocean. The diet consists of plankton and decaying organic matter found in the sea. It possesses an esophagus and stomach that opens into the intestine. The intestine is typically long and coiled, and loops through the body three times before terminating in a cloaca chamber, or directly as the anus.
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Arbacia punctulata (Purple-spine sea urchin)
Food enters the mouth, and then travels to the pharynx that opens up into the esophagus. The esophagus runs back down the outside of the lantern, to join the small intestine and a single caecum. The small intestine runs in a full circle around the inside of the test, before joining the large intestine, which completes another circuit in the opposite direction. Digestion occurs in the intestine, with the caecum producing further digestive enzymes. An additional tube, called the siphon, runs beside much of the intestine, opening into it at both ends. It may be involved in resorbing of water from food. From the large intestine, a rectum ascends towards the anus.
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