Umbrella-shaped and free-swimming basic body form of Cnidarians

APolyp

BHydra

CMedusa

DAuricle

Answer:

Phylum Cnidaria (Coelenterata):

They are aquatic, mostly marine, sessile (attached) or free-swimming
Radially symmetrical animals
Cnidarians exhibit tissue level of organization
They are diploblastic
The name cnidaria is derived from the cnidoblasts or cnidocytes (which contain the stinging capsules or nematocytes) present on the tentacles and the body.
Cnidarians exhibit two basic body forms called polyp and medusa.
The Polyp is a sessile and cylindrical form like Hydra, Adamsia, etc. whereas, the Medusa is umbrella-shaped and free-swimming like Aurelia or jelly fish.
Those cnidarians which exist in both forms exhibit alternation of generation (Metagenesis), i.e., polyps produce medusae asexually and medusae form the polyps sexually (e.g., Obelia).

Examples:

Challenger App