The escal light gland of the deep-sea anglerfish Haplophryne mollis (Pisces: Ceratioidei) with observations on luminescence control

Abstract

The escal light gland of three different-sized specimens of the deep-sea anglerfish Haplophryne mollis (family Linophrynidae) has been examined by light and electron microscopy. The light gland has a central cavity, with diverging branched ducts which ramify into numerous tightly-packed radial tubules. In the two largest specimens all glandular lumina contain symbiotic bacteria. Except for a thin-walled part of the typical radiating tubules, the epithelial walls of the light gland are of a uniform structure, consisting of flattened basal cells, situated next to the basal lamina, and tall cells extending to the lumen.In the smallest specimen examined the various parts of the light gland were not fully differentiated and only a very few symbiotic bacteria were present; its glandular epithelium differed from that of the two larger specimens by containing many goblet cells, the secretion of which may be important for the initial establishment of the right strain of symbiotic bacteriaObservations on the luminescence of live specimens have shown that the light emission can be rapidly modulated from within the esca. The in vivo flash kinetics are considerably slower than those of Dolopichthys longicornis, but similar to those of both the caruncle exudate of Ceratias holboelli and in vitro anglerfish bacterial luciferase.