|Catostylus mosaicus, blubber jellyfish|
Members of the family Catostylidae are small marine jellyfish with domed bells. The eight short oral arms are broad and three-sided. There is a network of branching canals linked with the primary ring canal, but these are not joined to the gastrovascular cavity except through the sixteen or thirty two radial canals. Some of these radial canals do not extend to the edge of the bell. There are eight sense organs, known as rhopalia, which have canals extending to the margin of the bell.
These jellyfish swim in jerks by contracting their circular and radial muscles, which decreases the volume of water enclosed under the bell, before relaxing them again and repeating the sequence. They have no control over the direction of locomotion and drift with the currents and tides.