Ctenophora (‘comb jellies’) A small phylum of carnivorous, hermaphroditic, marine animals, in which the body is biradially symmetrical and can be divided into two hemispheres, and into equal sections by eight ciliated bands, the ‘combs’ from which the phylum derives its common name. The cilia provide locomotive power in most species, although some lobate species swim by contracting the lobes. In the class Tentaculata two long, branched tentacles, armed with colloblasts, emerge from a deep canal in the epidermis on the aboral side of the body and are used to catch prey. Members of the class Nuda lack tentacles. Many ctenophores are spherical or ovoid, and 1–5 cm in diameter, but some are conical, cylindrical, or strap-like and one species of the genus Cestum grows to more than 1 m in length. Ctenophores have no definitive fossil record, but their body plan is similar to that of a medusa and they are believed to be descended from a medusoid cnidarian. There are two classes (Tentaculata with four orders, and Nuda with one order) altogether comprising about 50 species, some of which occur in coastal waters throughout the world, and others of which are oceanic.

Ctenophora A phylum of marine invertebrates that contains the comb jellies (e.g. Pleurobrachia). Like the closely related Cnidaria they are coelenterates; they possess tentacles armed with lasso cells, for catching prey, and many hundreds of thousands of cilia, which are fused at their bases and grouped together into longitudinal rows (comb plates or ctenes). The beating of the cilia enables these animals to swim among the plankton.