Mutations and rearrangements that occur by misalignment during DNA replication are frequent sources of genetic variation in bacteria. Dislocations between a replicating strand and its template at repetitive DNA sequences underlie the mechanism of these genetic events.
Cnidarians take on two basic forms, a medusa and a polyp. The medusa form is a free-swimming structure which consists of an umbrella-shaped body (called a bell), a fringe of tentacles that hang from the edge of the bell, a mouth opening located on the underside of the bell, and a gastrovascular cavity. The mesoglea layer of the medusa body wall is thick and jelly-like.
Cnidaria A phylum that comprises the sea anemones, jellyfish, and corals, and which is known from the late Precambrian. Cnidarians are basically radially symmetrical and have tentacles.The body contains a gastrovascular cavity and the body wall is diploblastic.Cnidarians occur as two distinct types: polyps and medusae, which in many taxa constitute alternating generations. All are aquatic and most are marine.wo body forms and two lifestyles are characteristic of the Cnidaria (see polyp and medusa). The sessile hydroid, or polyp, form is more or less cylindrical, attached to its substratum at its aboral (opposite the mouth) end, with the mouth and surrounding tentacles at the upper, oral, free end.