PROC. BIOL. SOC. WASH. 93(2), 1980, pp. 388-394 THE LARVA OF THE CONGRID EEL ACROMYCTER ALCOCKI (PISCES: ANGUILLIFORMES), AND THE DISTINCTION BETWEEN CONGRID AND OPHICHTHID LARVAE David G. Smith and Mark M. Leiby Abstract. — The larva of the congrid eel Acromycter alcocki is identified and described here for the first time on the basis of juvenile and metamor-phic specimens from Hawaii and the western Atlantic. It is an elongate leptocephalus with ten prominent, pigmented loops in the gut. In this it differs from other congrid larvae and approaches the condition found in certain ophichthids. On the other hand, some ophichthid larvae have the characteristic swellings of the gut reduced and approach the condition found in congrids. Aside from the presence or absence of intestinal swellings, the following characters will distinguish congrid from ophichthid larvae: the form of the liver and gall bladder, the degree of expansion of the gut between esophagus and intestine, the termination of the kidney relative to the anus, the nature of the pigment on the intestinal swellings and behind the anus, the form of the caudal fin, the number of branchiostegal rays, and the chon-drification of the basibranchials. The identification of larval eels with their corresponding adult forms has been an empirical process based largely on the fortuitous capture of meta-morphic specimens that combine the characters of larva and adult. When the larva of a particular species has been identified in this way, it is often possible to identify related species by inference even when metamorphic forms are not available. Over the years a framework of knowledge has been developed that has permitted a broad characterization of leptocephali of higher taxonomic groups. In this way most leptocephali can now be confi-dently identified to family even if the species is uncertain. Occasionally, however, the larva of a particular species may differ so sharply from its relatives that its true identity is not immediately evident. Such is the case presented here. The senior author located, in the Bernice P. Bishop Museum, a single juvenile specimen of the congrid eel Acromycter alcocki (Gilbert and Cra-mer) 116 mm in total length (Fig. 1). This specimen, the smallest yet seen of the genus Acromycter, had twelve large black spots on the ventral midline from shortly behind the head to shortly before the tip of the tail, and a thirteenth spot midlaterally between the last ventral spot and the tail tip. These are not seen in larger specimens and were interpreted as remnants of
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