Medusozoa

Medusozoa is the medusa phase.

Characteristics

Medusozoans differ from anthozoans in having the medusa stage in their life cycle. The basic pattern is medusa ordinarily the adult or sexual phase, planula larva, polyp, medusa. Symmetry is tetramerous, with parts in fours or multiples of four. The mitochondrial DNA molecules are linear rather than circular as in anthozoans and near all other animals. The cnidae, the explosive cells characteristic of the Cnidaria together with used in prey capture in addition to defence, are of a single type, there being nematocysts but no spirocysts or ptychocysts. In contrast, the anthozoan life cycle involves a planula larva which settles and becomes a sessile polyp, which is the grownup or sexual phase.