Genus Pachystomias

A scaleless dragonfish genus with a single species, the Smalltooth Dragonfish, Pachystomias microdon, found worldwide in oceanic midwaters - one of three stomiid genera with photophores that produce red light. Pachystomias microdon has evolved extremely specialized visual pigments capable of seeing this red light..

Pachystomias has a floor to its mouth with a membrane present between two halves of the lower jaw (mandibles); a short snout about equal to eye diameter; a simple chin barbel and jaws with many equally-spaced fang-like teeth. The dorsal fin is short-based and far back on the body, opposite the similars anal fin.

The crescent-shaped AOP photophore below the lower margin of the eye emits a red light.