Ctenophora

Ctenophora (or "Comb Bearers"), a class of Coelenterata, the members of which are provided with eight bands of cilia, known as ctenophores. They are non-colonial and free-swimming, and are all marine; as a rule they are globular in form, the mouth being situated at one pole and the two excretory apertures at the other; some, however, like Cestus or "Venus' Ribbon," are long and band-like. The mouth opens to a flat stomach, at the farther end of which is a "funnel," from which rise two canals ("perradial"); these bifurcate, and from each of the four "interradial vessels" thus formed there is given off a pair of vessels which lead to eight "ctenophoral vessels," lying below the ciliated plates. At the opposite pole to the month are the two openings of the excretory system, and between these is a small sensory organ or "ctenocyst," which is probably auditory. The Ctenophora all live on the surface of the sea; most of them swim by the action of the ciliated plates, but Cestus does so by snake-like undulations of its long ribbon-shaped body; as a rule they are small, but Cestus may be as much as five feet in length. Pleurobrachia is a very typical representative of the class, and is common all round the English coast; this and Beroe, which differs from it by the absence of the pair of long delicate tentacles, are both about an inch in length, and are usually mistaken for jellyfish, owing to their transparency and gelatinous consistency. The Ctenophora are of interest, as they resemble some worms of the order Polyclada (q.v.) in the possession of the mass of otoliths at the aboral pole and of the ciliated bands; an attempt has, therefore, been made to ally them with this group.