Cnidaria is a phylum containing over 10,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Cnidaria have two different body types, the swimming medusae and the sessile polyps. They both are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from endosymbiotic algae, and a few parasites.
Malo kingi (Box Jellyfish)
The Malo kingi is a jellyfish. Jellyfish don't have a specialized digestive system. The food enters through the mouth, which is located in the center of the bell. The food that goes into the mouth is trapped in the gastrovascular cavity and the nutrients are absorbed by the gastrodermis. The waste products of a jellyfish leave through the mouth. Jellyfish use their tentacles to poison the food they are trying to capture. Each tentacle has a large amount of nematocysts, which uncoil when the tentacle hits the prey.
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Diploria labyrinthiformis (grooved brain coral)
Coral has only one opening surrounded with tentacles. On each tentacle is a nematocyst. These nematocysts contain coiled stinging cells that paralyze their prey. The tentacles then move inward with the pray so that it can be moved into the mouth and down into the stomach cavity. Within this cavity there is mucus/mesentery, which helps break down the food. Due to having one hole, all waste is then excreted back through the mouth. Depending on their size, coral generally feed on plankton and small fish. Planktons are mostly active at night causing coral to be nocturnal feeders.
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Ceriantheopsis austroafricanus (Burrowing anemone)
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