Monopneumona

Sub-order of Dipnoi, including the single genus Ceratodus, an Australian herbivorous fish, with the swim-bladder functioning as a lung. The body is covered with large cycloid scales; the vomer bears incisor-like teeth, IMG:content-1418.png:[graphic] Narwhals. the left upper incisor, growing from a persistent pulp, and rarely present in the female. The lower jaw has no teeth; the other upper teeth are rudimentary. It lives in Arctic seas, and is known as the Sea-Unicorn.