STAR FISH
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The mouth of the starfish is found on the under side of the starfish 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 starfish. 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 starfish disposes waste) which is located in the central upper part of the body.
Sea Urchins
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The mouth of most sea urchins is made up of five calcium carbonate teeth or jaws, with a fleshy tongue-like structure within. The entire chewing organ is known as Aristotle's lantern. The lantern, where present, surrounds both the mouth cavity and the pharynx. At the top of the lantern, the pharynx opens into the esophagus, which 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. From the large intestine, a rectum ascends towards the anus. Despite the names, the small and large intestine of sea urchins are in no way homologous to the similarly named structures in vertebrates. 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 resorption of water from food.
Sea Cucumbers
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Holothuroidea are generally scavengers, feeding on debris in the benthic zone of the ocean. Exceptions include pelagic cucumbers and the species Rynkatropa pawsoni, which has a commensal relationship with deep-sea anglerfish. The diet of most cucumbers consists of plankton and decaying organic matter found in the sea. Some sea cucumbers position themselves in currents and catch food that flows by with their open tentacles. They also sift through the bottom sediments using their tentacles. A pharynx lies behind the mouth and is surrounded by a ring of ten calcareous plates. In most sea cucumbers, this is the only substantial part of the skeleton, and it forms the point of attachment for muscles that can retract the tentacles into the body for safety as for the main muscles of the body wall. Many species possess an oesophagus and stomach, but in some the pharynx opens directly into the intestine. The intestine is typically long and coiled, and loops through the body three times before terminating in a cloacal chamber, or directly as the anus.