Ctenophora; Print; Ctenophora comprise a phylum of invertebrate animals that live in marine waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"); and they are the largest animals to swim with the help of cilia. Depending on the species; adult ctenophores range from a few millimeters to 1.5 m (4 ft 11 in) in size. Only 100 to 150 species have been validated; and possibly another 25 have not been fully described and named. The textbook examples are cydippids with egg-shaped bodies and a pair of retractable tentacles fringed with tentilla ("little tentacles") that are covered with colloblasts; sticky cells that capture prey. Their bodies consist of a mass of jelly; with a layer two cells thick on the outside; and another lining the internal cavity. The phylum has a wide range of body forms; including the egg-shaped cydippids with retractable tentacles that capture prey; the flat generally combless platyctenids; and the large-mouthed beroids; which prey on other ctenophores.