Q.The symmetry exhibited in cnidarians is
a. Radial
b. Bilateral
c. Pentamerous radial
d. Asymmetrical

Cnidaria (Greek knide, sting), formerly Coelenterata, are aquatic animals — sessile or free-swimming, solitary or colonial — that are radially symmetrical except for the bilaterally symmetrical sea anemones. The name comes from cnidocytes (cnidoblasts), stinging cells bearing a nematocyst, used for anchorage, defence, and prey capture.

Cnidarians are the first phylum on the classification tree to show tissue-level organisation, remaining diploblastic. A single central cavity, the coelenteron, handles both digestion and circulation, opening to the outside through one mouth (hypostome) used for both ingestion and egestion; digestion is both extracellular and intracellular. The nervous system is a primitive, diffused nerve net.

Two body forms occur: the sessile, cylindrical polyp and the free-swimming, umbrella-shaped medusa. Species passing through both show alternation of generations (metagenesis) — polyps producing medusae asexually, medusae producing polyps sexually. Development is indirect, via a ciliated planula larva. Examples: Physalia (Portuguese man-of-war), Adamsia (sea anemone), Pennatula (sea pen), Meandrina (brain coral).