The photophore morphology of Selenoteuthis scintillans Voss and other lycoteuthids (Cephalopoda: Lycoteuthidae)

Females and juveniles of Selenoteuthis scintillans have photophores of several structural types, distributed on the tentacles and eyeballs, and within the mantle cavity and tail. Three distinct photophore types can be recognized on the basis of their accessory structures, though their photocytes are identical. The tail and some tentacular photophores (Type 1) lack any accessory optical structures; other tentacular and abdominal photophores (Type 2) have collagenous diffusing fibres; the anal and ocular photophores (Type 3) have a variety of iridosomes but no collagen. The distal tentacular organ is a double structure composed of a unit each of Type 1 and Type 2. Ocular photophores 1 and 5 are also double structures, composed of two Type 3 units. The photophores closely resemble in structure those of Lycoteuthis diadema. The photocytes have a marked fluorescence and luminesce on treatment with dilute hydrogen peroxide. The bio‐luminescence intensity of the tail organ may be modified by chromatophore movements and has a blue‐green spectral emission. The photophores of juvenile Lampadioteuthis megaleia are similar in structure to those of Selenoteuthis but somewhat less complex. A comparison between the morphology of the photophores of lycoteuthid and enoploteuthid squids emphasizes the close similarity between the two families. At the ultrastructural level, certain photophores of both families have very characteristic microvillous blood vessels associated with the photocytes.