medusozoans

Medusozoans are a subphylum of the phylum Cnidaria, encompassing all cnidarians that possess a medusa stage in their life cycle. This group includes jellyfish, box jellyfish, and hydroids, although the latter are primarily polypoid. The defining characteristic of medusozoans is the presence of a medusa, a bell-shaped or umbrella-shaped body form with tentacles hanging from its margin. This medusa stage is typically free-swimming and is the reproductive stage for most species.

The medusa stage is derived from the polyp stage in species with a biphasic life cycle, or it can develop directly from a larva in others. The medusa's body is composed of mesoglea, a gelatinous layer sandwiched between two layers of epithelial cells, the ectoderm and the endoderm. Cnidocytes, specialized stinging cells containing nematocysts, are abundant on the tentacles and are used for prey capture and defense.

Medusozoans exhibit a wide range of diversity in size, shape, and habitat. They are found in all marine environments, from shallow coastal waters to the deep ocean. Their ecological roles are significant, as they are both predators and prey within marine food webs. Reproduction in medusozoans can be sexual, with medusae releasing gametes into the water, or asexual, through budding from a polyp form. The subphylum Medusozoa is further divided into classes such as Scyphozoa (true jellyfish), Cubozoa (box jellyfish), Hydrozoa (hydroids and Portuguese man o' war), and Staurozoa (stalked jellyfish).