Dwarfed males parasitic on the females in oceanic angler-fishes (Pediculati ceratioidea)

Abstract

The fishes of the order Pediculati (Regan, 1912) form a remarkable assemblage of strange types, characterised by the structure of the spinous dorsal fin, which is composed of a few flexible rays, the first of these being placed on top of the head, not far behind the mouth, and modified into a line and bait. The Lophioid and Antennarioid Pediculates are for the most part dwellers on the bottom in shallow or moderately deep water, but the Ceratioids are oceanic, nearly all living in mid-water, between about 500 and 1500 metres below the surface. In relation to the darkness of their habitat they are generally blackish in colour, their eyes are small, and the bait, or terminal expansion of the first dorsal ray, is luminous. I have found dwarfed males, parasitic on the females, in two genera of Ceratioid Fishes. These are described below, and reasons are given for thinking that males of this type are characteristic of the group.