Cestida is an order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of comb jellies. It has one family, Cestidae, with two genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

: Cestum and Velamen, each containing one species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

.

• Cestum veneris Lesueur, 1813
• Velamen parallelum (Fol, 1869)

Unlike other comb jellies, the body of cestids is greatly flattened, and drawn out into a long ribbon-like shape. The two tentacle

Tentacle

A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...

s 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 metres (3.3 ft) in length.