Members of this class typically have two feathery tentacles that can be retracted into specialized sheaths. In some, there are smaller, secondary tentacles, and the primary tentacles are reduced. This class includes the small, oval sea gooseberries (genus Pleurobrachia), common on both Atlantic and Pacific coasts. The more flattened species of the genus Mnemiopsis, about 4 in. long (10 cm), is common on the upper Atlantic coast; it has a large mouth and feeds mainly on larval mollusks and copepods. This species is brilliantly luminescent. The similar, but larger, genus Leucothea is abundant on the Pacific coast. Venus's girdle (genus Cestum) is a flattened, ribbonlike form reaching over 1 yd (91 cm) in length, and found in tropical waters.
This class includes species that have no tentacles. Typical is the large-mouthed genus Beröe, which feeds on jellyfish and other ctenophores.
Any of nearly 90 species (phylum Ctenophora) of usually colourless marine invertebrates that have a series of vertical ciliary combs over their bodies. Ctenophores are sometimes mistaken for jellyfish. The body is round or spherical, with tentacles to capture food, and the combs beat to provide locomotion. Most species are small (not much greater than 0.1 in. [3 mm] in diameter), but at least one species grows larger than 3 ft (1 m). Ctenophores live in almost all ocean regions, floating freely in the water. All comb jellies except one parasitic species are carnivores, consuming young mollusks, crustacean and fish larvae, copepods, and other zooplankton.
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