On the integument and photophores of the alepocephalid fishesXenodermichthysandPhotostylus

Abstract

The mesopelagic alepocephalid fishesXenodermichthysandPhotostylushave unusual compartmented sub-dermal spaces filled with a fluid more dilute than sea water. The fluid is probably lymph, and contributes to the low density of the fish. The external layer superficial to these subdermal spaces consists of cells containing large intracellular paracrystals which form tubular arrays. This external layer is interrupted by numerous photophores (inPhotostylusborne on stalks) which have a reddish-violet central core, and are backed by a reflecting layer. The reflector does not contain guanine, it is made up of a series of flattened cells, and reflects blue-green light. The cells of the central core are assumed to be photocytes and are in connexion with apparent nerve terminals, but in neither fish has luminescence of the photophores been observed.