Chun, 1888
Trunk moderately compressed laterally (Megalocercus abyssorum). Mouth terminal. Buccal glands lacking. Gill slits elongate with a ciliated half circle in their anterior part. Esophagus short, strongly curved, entering the uppermost part of the stomach. Stomach undivided, lying on the intestine. Intestine arising from the upper right part of the stomach. Tail lacking either subchordal or amphichordal cells.
Two species recognized: Megalocercus abyssorum, recorded from the South Atlantic, and Megalocercus huxleyi, from the Indian and Pacific Oceans. Megalocercus atlanticus, described by Lohmann (1914) from the Brazilian coasts, was synonymized with Megalocercus abyssorum by Fenaux (1959, 1964).
Remark
The genera Chunopleura, Folia, Inopinata, Megalocercus, Mesoikopleura, Mesopelagica, Oikopleura, and Stegosoma are grouped together under the supergenus Labiata Fenaux, 1993.