The Sequence of Photophore Development inXenodermichthys Copei(Pisces: Alepocephalidae)

Abstract

In the family Alepocephalidae there areca. 19 valid genera (Markle, personal communication). Whilst luminescence has never been observed, there are four genera,Xenodermichthys, Photostylus, RouleinaandMicrophotolepis, which contain species bearing structures that have been interpreted anatomically as photophores (Herring & Morin, 1978). Among these four there is a remarkable diversity of photophore structure. The photophores ofXenodermichthysandPhotostylusare similar in having well developed central cores (reddish violet inXenodermichthys) and reflector layers, yet those ofXenodermichthysare sessile whilst those ofPhotostylusare borne on stalks (e.g. von Lendenfeld, 1887; Best & Bone, 1976). Not all species ofRouleinahave light organs but where they are present they are sessile. Photophore structure ofRouleinahas been examined only inR. maderensisMaul and was found there to be rather degenerate in adults (Markle, 1978). The light organs ofMicrophotolepis multipunctataSazanov and Parin differ yet again in being scale covered, which contrasts with the naked photophores in the other three genera (Sazanov & Parin, 1977). The abundance and distribution of photophores in adults also varies with genus and species. Thus inMicrophotolepisandXenodermichthysthey are extremely numerous and regularly arranged but inPhotostylusthey are few and less ordered (Günther, 1887; Beebe, 1933; Sazanov & Parin, 1977). In different species ofRouleinaphotophores may be relatively abundant and regularly arranged or few in number without such regular pattern (Maul, 1948; Uyeno & Kishida, 1977; Markle, 1978).