Echinodermata The echinoderm is of the Phylum Echinodermata, which is a phylum of marine animals. This Phylum includes about 70,000 living species such as sea stars, sea urchins, sand dollars, and sea cucumbers. This number makes the Echinodermata the largest phylum that has no freshwater of terrestrial representatives. Digestion When an echinoderm ingests food, the first step on the path it takes is the mouth, which is on the bottom of the organism. After the mouth, the food travels through the esophagus and into one of the two stomachs of an echinoderm; the cardiac stomach. Some echinoderms can actually take their cardiac stomachs outside of their body. For example, starfish open a bivalve with their strong water-vascular system and push their stomachs inside to digest their prey. Next, the food travels into the pyloric stomach where it is continued to be digested. The last steps of digestion take place in the intestine and digestive glands. Waste is then excreted through the anus. The Digestive System of the Echinoderm Some echinoderms such as Sea Stars, Brittle Stars, and Sea Lilies are carnivorous, while others such as Feather Stars, are filter feeders and feed on phytoplankton- one-celled free floating algae found in plankton. These different types of diets result in different kinds of digestive systems. The three animals of the Echinodermata Phylum whose digestive systems we shall go over are sea stars, sea cucumbers, and sea urchins. The Digestive System of the Sea Star The physical make-up of a sea stars digestion system is as follows: The mouth of the sea star is found on the under side of the sea star creature. 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 much 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. Some species of Sea Stars eat their prey hole and begin digesting it before sending it to the digestive glands in the Sea Stars arms. Other Sea Star species are able to put their stomach outside their bodies, where it can eat food and begin the digestion process. It passes this food to its secondary stomach, which always stays inside the Sea Star. Further digestion occurs at the Sea Stars intestine. Finally, waste is excreted through the Sea Stars anus on its aboral side of the body. The Digestive System of the Sea Cucumber Sea cucumbers are mostly scavengers that feed on debris in the benthic zone of the ocean. While the diet of most Sea Cucumbers consists of plankton and decaying organic matter found in the sea, others position themselves in the currents and catch food that flows bye with their tenticles. Many species possess an oesophagus and stomach, but in some the pharynx opens directly into the intenstine. The intestine is typically long and coiled, and loops through the body three times before terminating in a cloacol chamber, or directly as the anus. The Digestive System of the Sea Urchin Along with the five gonads, the Sea Urchins digestive tact takes up most of the internal space of the Sea Urchin. Sea Urchins are most known for eating kelp,but will eat sponges and other invertebrates as well. Waste is expelled through the Sea Urchins anus, which is located at the top of its body.
Posted on: Sat, 15 Mar 2014 16:45:59 +0000
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