SCANNING ELECTRON-MICROSCOPIC OBSERVATIONS ON THE HEAD MORPHOLOGY OF 7 DIFFERENT LEPTOCEPHALI BELONGING TO 6 EEL FAMILIES (ANGUILLIFORMES)

Scanning electron microscopy observation was carried out on head morph ology, number and construction of teeth, nostril position and the pres ence of neuromasts of seven species of leptocephali from six families of the Anguilliformes. The number and form of the teeth vary within th e different families, from 76 teeth in Gnathophis sp. (Congridae) to 3 2 teeth in Anarchias yoshiae (Muraenidae). In most of the genera the n umber of teeth on upper and lower jaws is almost equal, except in Gnat hophis sp., Anguilla anguilla and Kaupichthys hyoproroides. The unusua l size and form of the leptocephali's teeth led us to speculate on the feeding behaviour of these larvae. Tentatively we suggest that the to oth formation of the leptocephali may act as a filtering system, rathe r than as a predatory apparatus, as its vicious appearance might sugge st. Given the largely passive nature of a filtering system, the larvae would be able to concentrate on their migration. Of all the investiga ted leptocephali, only Nemichthys scolopaceus shows one olfactory open ing on each side of the head, whilst all the other species show two op enings. 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,