INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 1 - H.I. Shcherbak - 1995

SUBKINGDOM MULTICELLULAR ANIMALS (METAZOA)

SECTION TRUE METAZOANS (EUMETAZOA)

PHYLUM CTENOPHORA

This phylum comprises exclusively marine animals. There are about 120 known species of ctenophores, the majority of which inhabit tropical seas, while in polar regions certain species form dense aggregations. Only a single species, Pleurobrachia rhodopis, is found in the Black and Azov seas, having appeared there relatively recently. Ctenophores are predominantly free-swimming predators, although crawling and sessile detritivorous species are also known. Their size ranges from 2–3 mm (such as the blue tinerfe, Tinerfe cyanea) to 2.5 m (Venus' girdle, Cestus veneris).

Ctenophores are radially symmetrical, diploblastic animals (possessing a rudimentary mesoderm) which, unlike Cnidaria, lack stinging Cells, a polypoid developmental phase, and metagenesis. Their body plan is characterized by a combination of eight-ray and biradial Symmetry. Unlike Cnidaria, ctenophores move by means of modified cilia arranged as comb rows. They are hermaphroditic with external Fertilization and direct development. The phylum includes a single Class, Ctenophora.