The Molidae comprise the family of the molas or ocean sunfishes, unusual fish whose bodies come to an end just behind the dorsal and anal fins, giving them a "half-fish" appearance.

They are also the largest of the ray-finned bony fish, with the southern sunfish, Mola alexandrini, recorded at 4.6 m (15 ft) in length[3] and 2,744 kg (6,049 lb) in weight.

This layer, which is horizontally separated by a septum, provides the fish with buoyancy, and makes up a larger part of the animal's total mass the bigger the individual is.

The molid signals a readiness for cleaning by swimming almost vertically with its head near the surface of the water, and waits for the smaller cleaner fish to feed on the parasite worms.

[1] The fossil genus Austromola containing one species, A. angerhoferi Gregorova, Schultz, Harzhauser & Kroh, 2009, is known from the Lower Miocene Ebelsberg Formation near Pucking, Austria.