AP BIOLOGY

Detailed explanation-1: -Cnidaria is derived from a Greek word “cnidos” meaning stinging thread. These entities are characterized by the presence of cnidae. Cnidaria is a phylum under Animalia Kingdom, a classification comprising 10, 000 described species, some of them are corals, sea anemones, jellyfishes and hydras.

Detailed explanation-2: -In the phylum Cnidaria, which includes jellyfish and sea anemones, polyp and medusa are two different stages of the life cycle. In some species, these two stages alternate between each other, such as in Hydrozoa.

Detailed explanation-3: -Scyphozoans are the more commonly thought of Cnidarians. They have a true medusa stage and can be very large. This are often referred to as Jellyfish, the largest one known can have a bell over 10ft in diameter.

Detailed explanation-4: -Cnidarians are radially or biradially symmetric, a general type of symmetry believed primitive for eumetazoans. They have achieved the tissue level of organization, in which some similar cells are associated into groups or aggregations called tissues, but true organs do not occur.

Detailed explanation-5: -The body plans cnidarians generally have radial symmetry (Fig. 3.25 A). Because the tentacles of corals, jellyfish, and sea anemones have this radial structure, they can sting and capture food coming from any direction.