CTENOPHORA, te-non-ra (Neo-Lat. nom. pl., from Gk. KTE1S, ktcis, comb + OepeLv, phe rein, to bear, carry). A class of eadenterates, composed of jellyfish, characterized by the ab sence of nettle-cells and the near approach to bilateral symmetry. The ctenophores are dis tinguished by the presence of eight external rows of minute plates, made from fused cilia, begin ning near the aboral pole and running down to ward the mouth, which have given the name 'comb-jellies' to this group. The body is almost transparent, and is oval, more or less elongated, rarely band-shaped, as in the girdle-of-Venus (q.v.). The gastrovascular system of canals is rather complicated and differs from that of other cielenterates by opening at the aboral pole, with two small outlets: between these is a remark able and complicated sense-organ, which serves as an eye and a positional organ. The body is often prolonged on each side of the mouth as a flap or fold, by the movements of which the ani mals swim. The eight rows of so-called swim
ming plates are probably quite as much respira tory as locomotive. On each side of the body is a long tentacle, with branches on one side, capa ble of being greatly extended or completely re tracted into a protecting sheath. In a few forms these tentacles are wanting. More than 100 species of ctenophores are known, all marine. The largest ones are only three or four inches in length, but the girdle-of-Venus is sometimes five feet broad. They are usually colorless, but are sometimes yellowish or brownish, and the move ment of the swimming plates sometimes makes them strikingly iridescent. Many species are notably phosphorescent. Consult: L. Agassiz, Contributions to the Natural History of the Fruited States, vol. iii., pt. 2 (Boston. I860) A. Agassiz, papers in Memoirs of the Museum. of Comparatire Zolilogy (Cambridge, Mass., 1375 et seq.). See CtELENTERATA.