Structural features related to habits of life are described for the thermosbænacean Monodella argentarii. Although it can swim, this minute malacostracan is essentially benthic in habits, and its food consists of bottom detritus. The collection and subsequent manipulation of food are described. Monodella is not a filter feeder and no currents are involved in the feeding process which consists essentially of scraping, brushing and pushing. Cephalic appendages only are involved. The structure and mode of action of the mouthparts are described and illustrated in detail, and the functional significance of many structural features is explained.

No justification is found for placing the Thermosbænacea in a separate division, the Pancarida, and its position within the Peracarida is discussed.

The past history and present distribution of the Thermosbænacea are reconsidered.