This is a small phylum with fewer than 100 known species divided into two Classes. They are all marine and mainly found in warm waters. Most species are small, but some can grow up to 2 m long. Their common name, "comb jellies", comes from the eight comb rows of cilia that are used in locomotion. They are the largest animals to use cilia for locomotion. The threads in the colloblasts wrap around the prey entangling it. They have the ability to luminesce from chemical reactions in the gastrodermis. They have a statocyst containing a calcareous statolith which gives the animal information about its position and orientation.

Class Tentaculata

All in this class have two tentacles; a characteristic species is Hormimorpha plumosa seen on the right. Some in this class are flattened into a ribbon-like shape along the plane of the tentacles and have an undulatory motion. Cestium sp., above, is an example. It can grow to over 100 cm in length.

Class Nuda

These do not have tentacles at any stage in their lives; a characteristic species is Beroe punctatus, left. Another in the Beroe genus can be seen below, these can be over 10 cm long and 5 cm wide.