Evidence of comparative and developmental morphology is presented from 99 specimens from the Atlantic and Indian Oceans to establish the conspecificity of Benthalbella dubius with B. irfans. The development of the species is described from the early post-larva (12.5 mm) through metamorphosis (60–80 mm) to the sexually mature adult (112–143 mm). Benthalbella infans is shown to be a hermaphrodite with simultaneous maturation of ova and spermatozoa, in common with other alepisauroid fishes. A fecundity estimate gave 2300 ova. The morphology and histology of the light organs are described, at cellular and sub-cellular levels, and the luminous tissue is shown to be derived from muscle blocks. The significance of these findings is discussed, the properties of the bioluminescent emission defined and measures of intensity recorded. Stomach contents were analysed. The significance of changes in body and eye orientation at ossification is discussed in relation to behaviour and specifically to that of feeding. The horizontal and vertical distribution of B. infans considered in the light of collections made in the eastern North Atlantic. The possibility of racial differences within the species is discussed, although no major niorphological differences were observed between Atlantic and Indian Ocean specimens. The diurnal depth distribution of the species is indicated (90–1500 m); post-larvae are shown to occupy the shallower reaches of the range, descending with advancing development. Evidence of vertical migration was observed only in adults and juveniles.