They are distinguished from other comb jellies by their spherical or oval bodies, and the fact their tentacles are branched, and can be retracted into pouches on either side of the pharynx.

[2] From opposite sides of the body extends a pair of long, slender tentacles, each housed in a sheath into which it can be withdrawn.

The function of the spiral thread is uncertain, but it may absorb stress when prey tries to escape, and thus prevent the colloblast from being torn apart.

[5] There are eight rows of combs that run from near the mouth to the opposite end, and are spaced evenly round the body.

This forms a mechanical system for transmitting the beat rhythm from the combs to the balancers, via water disturbances created by the cilia.