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.
There are about 10,000 species found in this phylum. The key characteristic features of cnidarians include radial symmetry, acoelomate body with tissues, lack of organs, and the simple digestive sac that opens through a mouth, which is surrounded by tentacles armed with nematocysts.All cnidarians are carnivores and have very simple body structures adapted as predators.he key characteristic features of cnidarians include radial symmetry, acoelomate body with tissues, lack of organs, and the simple digestive sac that opens through a mouth, which is surrounded by tentacles armed with nematocysts.