Cestida

Cestida is an order of comb jellies. It has one family, Cestidae, with two genera: Cestum and Velamen, each containing one species.

Unlike other comb jellies, the body of cestids is greatly flattened, and drawn out into a long ribbon-like shape. The two tentacles are greatly shortened, and two of the four ciliated comb rows are reduced. The unusual body form allows the animals to swim by means of muscular undulation, as well as by using their cilia. The largest species, belonging to the genus Cestum, can reach 1 metre (3.3 ft) in length.