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Monognathus jesperseni.jpg
Comparison of M. jesperseni with Eupharynx
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Saccopharyngiformes
Family: Monognathidae
Genus: Monognathus
Bertin, 1936

15, see text.

Monognathus, or onejaw, is the only genus of the family Monognathidae of deep-sea, eel-like fishes. The name comes from the Greek monos meaning “one” and gnathos meaning “jaw”, a reference to the large mouth in comparison with the rest of the fish, and also the absence of an upper jaw (maxilla and premaxilla bones are absent). The dorsal and anal fins lack bony supports and the pectoral fins are missing. The snout has a fang which is connected to glands.

Typical lengths are from 4 to 10 cm (1.5–4 in), the maximum length recorded is 15.9 cm (6.3 in).

They are generally black in color[citation needed], and are found at depths of over 2,000 m (6,600 ft).[1]


The fifteen known species are:[1]


  1. ^ a b Froese, Rainer, and Daniel Pauly, eds. (2011). "Monognathidae" in FishBase. June 2011 version.