BULLETIN OF MARINE SCIENCE, 60(1): 6-22, 1997 GARDEN EEL LEPTOCEPHALI: CHARACTERS, GENERIC IDENTIFICATION, DISTRIBUTION, AND RELATIONSHIPS P. H. J. Castle ABSTRACT More than 30 species of garden eels (AnguilIiformes, Congridae, Heterocongrinae) are now known. worldwide, including several that are undescribed. The leptocephali of Hetero- conger Bleeker have been described from the Atlantic and East Pacific, but little is otherwise known of the early life history of these eels. Study of the large collection of garden eel larvae in the Dana collections, Copenhagen (around 600 specimens), and other material, now allows the larval form of Gorgasia Meek and Hildebrand to be identified, and the distribution of several Indo-west Pacific species to be mapped. Heteroconger leptocephali have midlateral melanophores on the myotomes as in the larvae of most genera of Congrinae, and Paraconger and Chiloconger in the Bathymyrinae. Those of Gorgasia have a different pigmentation pattern consisting mainly of compact melanophores on the myosepta below the midlateral level. A third larval type, l.eptocephalus maculatus Della Croce and Castle, 1966 has scat- tered melanophores over the body surface and is identified with Heteroconger hassi (Klau- sewitz and Eibl-Eibesfeldt, 1959), The pigment pattern of Gorgasia, though distinctive, is similar to that of the bathymyrine Ariosoma and its closer allies, to Benthenchelys and other Ophichthidae and unexpectedly to Muraenesox, Additionally, some skeletal characters and the common use of tail-first burrowing behavior suggest that a more comprehensive study of the relationship between the heterocongrines, the bathymyrines and the Ophichthidae in par- ticular, is warranted, Garden eels are generally agreed to comprise their own subfamily, the Heter- ocongrinae and have distinctive form and habits that separate them from the two other larger subfamilies of the Congridae, the Bathymyrinae and Congrinae, Smith (1989a) summarises what is known about these eels. They occur almost exclusively in the tropical to subtropical ocean, mostly in relatively shallow water, though they have been collected in water as deep as 200-300 m. They are usually observed in groups of several individuals to hundreds, though they may form aggregations of several thousand. They are most often seen burrowed tail-first in, but semi-emergent from loose, coral "sand" off the outer edge of reefs or shores, in localities of some current, though they are also known from mixed broken rubble and sand. Although some 35 or so garden eel species are known worldwide, some of these have yet to be formally described. Most species occur in the Indo-Pacific, with several in the East Pacific and two or three in the Atlantic. The species are clearly separated into the two genera Heteroconger Bleeker, 1853 with its type species H. polyzona Bleeker from central Indonesia, and Gorgasia Meek and Hildebrand, 1923, with type species G. punctata Meek and Hildebrand from Pa- cific Panama. Several other genera have been described but were judged by Bohlke and Randall (1981) to be synonyms of Heteroconger because the principal distinctions were made on the degree of reduction (or absence) of the pectoral and caudal fins. This character is not consistent enough to be used. A thorough appraisal of species inter-·relationships within this remarkable subfamily and its position relative to the other Congridae, has yet to be made. Garden eels are very slender, long-bodied fishes in which the snout is very short and the mouth is terminal and markedly oblique. The eyes are relatively 6 CASTLE: GARDEN EEL LEPTOCEPHALI 7 Gorgasia pll1lctata ~ ~. .,,;a . (L.J'-= .. _<::---=----~ --- •• •~.--8';;--"=-- -- anterior nostril upper lip Figure 1. External differences between Gorgasia and Heteroconger. Ethmoid pore is arrowed. large and face more or less directly forwards. The pectoral fin is short, minute or even absent and the caudal fin is also short or fleshy and pointed. The principal skeletal features are the strong, forwardly-directed jaw support associated with the terminal mouth, and the reduction of the neural arches and spines along most of the vertebral column, except for the first few and the penultimate 10-12. The immediate postcranial region and the end of the tail are concerned, respectively, with the flexing horizontally forwards of the anterior part of the body as it emerg- es from the burrow in which the eel lives, and the action of the caudal region in digging tail-first into sediments. Species of Heteroconger have upper lips that form a single, prominent, conflu- ent flange across the face of the snout that encloses tiny, subtubular, forwardly- directed anterior nostrils and the ethmoid sensory pores (Fig. 1). The snout is very short or pug-nosed and the oblique mouth barely reaches to below the an- terior margin of eye. The teeth form broad bands on all surfaces, except that the posterior half of the maxilla is curved outwards and has teeth that tend to be uniserial and enlarged. There are few head pores and the pectoral fin is a tiny, fleshy flap (or absent in H. polyzona except for the occasional specimen in which it is a small tab of skin). The Heteroconger species are typically spotted, speckled or banded in body coloration. In contrast, species of Gorgasia have upper lips that are separate medially and do not enclose the anterior nostrils and ethmoid pores (Fig. 1). The snout is somewhat longer and less blunt, the gape is oblique but longer, reaching to below middle of pupil, and the teeth form narrower bands or are even uniserial on the vomer. The complement of head pores is mOrecomplete though those of the lateral line proper may be rather widely spaced and fewer than the number of vertebrae. With one or two notable exceptions the body color of the Gorgasia species is dull or nondescript. 8 BULLETINOFMARINESCIENCE,VOL.60, NO.I, 1997 The Heterocongrinae is currently regarded as a highly specialized congrid sub- family lineage, more closely related to the Bathymyrinae (Ariosoma, Bathymyrus etc,) than to the Congrinae (Conger and its many allies). This view was developed more thoroughly by Smith (1989a) from comprehensive studies on adults of all but a few congrid genera, Larval characters were apparently not explored to any extent by Smith (l989a). Though the larvae of Heteroconger had been known for some time (Blache, 1977; Raju, 1974, 1985; Smith, 1989b), those of Gorgasia had not been described under that name, except incidentally and without detailed comment by Castle (1984). As will be made clear later, Gorgasia larvae were in fact described earlier by D'Ancona (1928) from the Red Sea, by Blache (1977) from the East Atlantic and by Smith (1989b) from the western Atlantic, but not identified as such. Raju (1974, 1985) erred in referring his 65-95 mm TL specimens from the Pacific coast of Mexico (SIO 61·-248, 75-249) that had midlateral melanophores, to Gor- gasia punctata. These were apparently Heteroconger larvae with regenerated tails and the metamorphic larva of G, obtusa (Garman, 1899) from Pacific Panama was apparently that of the bathymyrine eel Chiloconger labiatus Myers and Wade, 1941 (D. G, Smith, pers. comm.). The discovery of metamorphic specimens of Gorgasia maculata Klausewitz and Eibl-Eibesfeldt, 1959, allows Gorgasia larvae to be identified, collections of garden eel larvae to be adequately sorted, and an assessment of the contribution that larval characters might make to exploring relationships of the Heterocongri- nae to proceed. Accordingly, this paper distinguishes between the larvae of the two garden eel genera, describes the distribution of larvae of several species in the Indo-Pacific and attempts to evaluate the relationships of the garden eels based on larval and some adult characters, MATERIALS AND METHODS Specimens discussed in this paper were derived from a variety of sources. Leptocephali were mostly from the Danish DANAExpedition Round the World 1928-1930 collections now held in the University Zoological Museum, Copenhagen (ZMUC). A few others were from the western South Pacific col- lections of ORSTOM, Noumea. A range of adult specimens and species were loaned mainly from United States institutions. Institutional acronyms, where available, are as given in Leviton et a1.(1985). Vertebral counts were made from radiographs. My observations show that garden eels seldom lose their tail tips, as is very common in eels such as species of the congrid eel genus Bathycongrus, so vertebral counts can be considered reliable. There is a likelihood of some small error in estimating total numbers of larval myome:res because of difficulty in counting the last one or two myomeres. This might explain slight differences in mean vertebral counts and myomeres given for the species discussed in this paper, GENERIC CHARACTERS AND IDENTIFICATION OF THE LARVAE The larvae of Heteroconger (Fig. 2), have a short gut (anus placed near mid- length in full grown individuals) and in this respect are like those of Muraenesox in the Muraenesocidae. In contrast, the anus is subterminal in the Ariosoma group, and well back in other congrids. However, in pigmentation Heteroconger larvae are rather like those of several genera of Congrinae. They have a series of paired, ocellate melanophores along the gut and a midlateral series of spaced, ocellate or rather diffuse melanophores on the surface of the myomeres, with one on each myomere in H. longissimus (Gunther, 1970), in Heteroconger sp. (Blache, 1977) and more or less so in H. luteolus Smith, 1989. These are Atlantic species, but in the Indo-west Pacific species the midlateral melanophores are fewer and much more widely spaced. Metamorphic and juvenile specimens were described from the East Pacific by Raju (1985) under the names H. digueti (Pellegrin, 1923) and CASTLE: GARDEN EEL LEPTOCEPHALI 9 Figure 2. Heleroconger sp., leptocephali (A-C) and metamorphic specimen (D-E). A, 39.3 mm TL, ORSTOM station S2, 8 June 1962; B-C, 92.3 mm TL, ORSTOM station S2, 8 June 1962; D-E, 76 mm TL, ZMUC P312678, Vanadoro Harbour, Philippine Islands, 22 July 1908; F, ZMUC P312678 (same as D and E), pigmentation of posterior part of gut.