Scanning electron microscopic observations on the head morphology of seven different leptocephali belonging to six eel families (Anguilliformes)

Scanning electron microscopy observation was carried out on head morphology, number and construction of teeth, nostril position and the presence of neuromasts of seven species of leptocephali from six families of the Anguilliformes. The number and form of the teeth vary within the different families, from 76 teeth inGnathophis sp. (Congridae) to 32 teeth inAnarchias yoshiae (Muraenidae). In most of the genera the number of teeth on upper and lower jaws is almost equal, except inGnathophis sp.,Anguilla anguilla andKaupichthys hyoproroides. The unusual size and form of the leptocephali's teeth led us to speculate on the feeding behaviour of these larvae. Tentatively we suggest that the tooth formation of the leptocephali may act as a filtering system, rather than as a predatory apparatus, as its vicious appearance might suggest. Given the largely passive nature of a filtering system, the larvae would be able to concentrate on their migration. Of all the investigated leptocephali, onlyNemichthys scolopaceus shows one olfactory opening on each side of the head, whilst all the other species show two openings. The data obtained from these investigations suggest that teeth form as well as form and position of the nostrils are characteristics of the genera, and possibly also of the species.