Characteristics of the Family (from Kramp 1961)
Rhizostomes with mouth-arms dichotomous and triangular or three-winged. A network of anastomosing canals communicate with the central gastral cavity in several places between the radial canals. Rhopalar pits smooth, without radial folds. Subgenital ostia without papillae.
With subumrellar muscles in feather-like arcs. Radial canals usually about twice as many as rhopalia (more or less than 32). Without or with faintly indicated ring canal. With four completely separated subgenital cavities. Subgenital ostia small, round. Stomach circular. Arm disk octagonal, with four primary canals.
Eight pinnately or irregularly branched mouth-arms with ventral mouth-openings only and large or small vesicles; ring canal absent or faintly indicated; usually with 16 rhopalar and about 16 (or more) inter-rhopalar canals.