Cnidaria


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What are they?

Cnidaria is a phylum of Animals which live in the water, and there are over 9000 species in the phylum. All cnidaria contain a unique cell, called cnidocytes. Cnidaria can have two body forms, medusae and sessile polyps. Some cnidaria alternate between these states, while others stay in one. Medusae are umbrella shaped, with tentacles hanging down, and they are swimming. Polyps are usually non-moving, cylindrical, and can be independant, or join with other polyps to form colonies.

Cnidocytes

Cnidocytes are also known as cnidoblasts, or nematocytes, and they are venomous. Each cnidocyte cell contains a unique organelle called a cnidocyst. Inside this organelle is a capsule connected to a coiled, hollow thread. The cell has a hair like projection out of it, which when touched triggers the projection to fire out at an acceleration of up to 5,400,000g. One of the most common types of cnidocytes contains barbs on the capsule, which allows it to penetrate its victim and inject the venom


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