BULLETIN OF MARINE SCIENCE, 28(3): 442-486, 1978 LEPTOCEPHALI OF THE OPHICHTHID GENERA AHLIA, MYROPHIS, OPHICHTHUS, PISODONOPHIS, CALLECHELYS, LETHARCHUS, AND APTERICHTUS ON THE ATLANTIC CONTINENTAL SHELF OF THE UNITED STATES Michael P. Fahay and Cinda L. Obenchain ABSTRACT Twelve leptocephali of the family Ophichthidae are described and j]]ustrated. Eleven types are specifically identified: Ahlia egmontis, Myrophis punetatus, M. platyrhynelllls, Ophiehthlls ophis, O. melanoporus, O. oeellatlls, O. gomesi, Pisodonophis crl/entifer, LetharchllS velifer, Apteriehtlls ansp, and A. kendalli. One type is assigned to the genus Callecllelys. Distribution maps showing capture locations on the Atlantic continental shelf are included for each type. Monthly length-frequencies are provided for ]0 of the more abundant types. Morphometric tables showing changes in bodily proportions with growth are included for nine types. The larval evidence supports McCosker's (1977) removing Echeills from the subfamily Myrophinae and reassigning it to the Ophichthinae. We discuss the generic identification of nominal Pisodonophis eruentifer, acknowledge the dissimilarity of that species to eastern Atlantic and Pacific Pisodonopllis, but question assigning P. crllentifer to Oplliehthus (McCosker, 1977). Western Atlantic P. eruentifer larvae are shown to be significantly different from Ophiehthus larvae. The degree of gut looping in ophichthid leptocephali is related to the amount and nature of pigmentation, and both larval characters are related to body elongation and fin reduction in adults. The leptocephali of A hlia have weakly swollen guts and scattered pigment patterns and the adults are relatively thick-bodied and retain a wide-based pectoral fin and high median fins. The leptocephali of Apterichtus have strongly looped guts and consolidated pigment patterns and the adults are relatively elongate and lack all fins. Genera between these extremes display a progression of both larval and adult characters. Ophichthid leptocephali are the most com- vius (1763) to describe an eel larva later monly collected eel larvae along the Atlantic shown to be Conger conger. Western North continental shelf and are the most numerous Atlantic representatives of this nominal genus among the eight anguilliform families repre- include: L. caribbaeus Fowler, 1944; L. sented in the Sandy Hook Laboratory's ich- caudomaculatus Eigenmann and Kennedy, thyoplankton collection. Despite the large 1902; L. eigenmanni Lea, 1913; L. humilis number of species occurring in the western Stromman, 1896; L. morrisii Eigenmann and North Atlantic as adults (as many as 39) and Kennedy, 1902; and L. mucronatus Eigen- the relative abundance of leptocephali, the mann and Kennedy, 1902. All of these will early life-history stages of only two species be referred to ophichthid species in this have been described. Eldred (1966) de- paper. scribed the development of Myrophis punc- Eels of the family Ophichthidae are among tatus from the prelarva to the metamorphos- the most ecologically specialized of teleosts ing elver. Richardson (1974) described the and this specialization is reflected in a variety eggs and early larvae of Pisodonophis cruen- of leptocephalus larval stages. Ophichthid tifer. Several other ophichthids have been leptocephali are characterized by three or described and assigned to the nominal genus more loops or swellings along the gut which Leptocephalus, a name proposed by Grono- range from mildly thickened bulges (in the 442 FAHAY AND OBENCHAIN: OPHICHTHID LEPTOCEPHALI 443 genus Ophichthus) to wildly festooned loops fied leptocephali should be weighed before (in the genus Apterichtus). Ventral pigment adding to the already confused literature. is usually concentrated on the thickenings or Favoring the practice are the following facts: loops of the gut. Pigment along the body (1) The leptocephali of most eel species be- midline ranges from a scattered pattern of cause of their pelagic mode of life are much small spots on each myoseptum (in the genus easier to collect than the adult stages, most Ophichthus) to a consolidation of pigment of which are by their nature secretive or into a few, bold, eye-sized blotches (in the burrowing forms which even if encountered genus Apterichtus). In the subfamily are difficult to contain within the meshes of Ophichthinae, the absence of a caudal fin in a net. In most cases then, if the identification adults begins in early metamorphosis with of larvae must await the assemblage of large the reduction of the larval finfold to a hard, numbers of juveniles and adults, the wait pointed tip. Members of the other subfamily could be a long one and the result might be (Myrophinae) retain the caudal fin but the the sequestering of larval collections to the leptocephali are recognizable by character- limbo of dusty collection shelves. (2) Lepto- istic short-based opisthonephroi located over cephali are widely diverse at the generic level the terminus of the gut and by pronounced while adults tend toward a morphological third gut swellings. conformity, related no doubt to the develop- Myrophines are further characterized by a ment of crevice-dwelling or sand-burrowing vent which migrates only slightly during habits (Castle, 1969). Thus, the study of metamorphosis. Thus, within a species, the larval types (named or not) might reflect number of preanal myomeres in the lepto- phylogenetic relationships not always ap- cephalus closely approximates the number of parent in the adults. (3) Most, if not all, preanal vertebrae in the adult. This condi- eel systematic work is based on adult ma- tion is found, in other anguiIIiforms, only in terial, but larval information may be an the family Moringuidae. Both moringuid and asset to workers in adult systematics as rein- myrophine larvae have short-based opistho- forcement material. The work on myc- nephroi associated with gut loops near the tophids (Moser and Ahlstrom, 1974) is an vent. Whether this opisthonephros-gut loop example of this application of larval studies. development is related to the nearly static (4) Larval information may be an asset (as vent position is unknown but it is tempting comparative data) to other workers in larval to speculate that such is the case. systematics. Because of the bizarre structure of lepto- Arguments against the practice include cephali and the relative ease with which the following: (1) As described leptocephali larvae are collected compared with the diffi- are finally linked to known adults, many culty in collecting adults, it has been the specific name changes will be required, since practice to publish descriptions of the more many "Leptocephalus" names antedate the distinctive types without knowledge of their adult names. (2) Most "species" of Lepto- specific identity. This has resulted in the ad- cephalus are actually groups of species, and dition to the literature of lettered or num- name changes may result in single species bered unknowns (i.e., "Species I," "Species being confused for a group. (3) The genus A," "Species 9a*") or species within the Leptocephalus simply has no validity as a nominal genus Leptocephalus. Castle (1969), generic grouping since it consists of a multi- in a thorough search of the literature, found tude of species, genera, and families. (4) descriptions of 70 distinct forms of eel larvae Assigning a distinctive larva to the genus designated by letters or numbers alone, and Leptocephalus pending a later linking to an more than 200 distinct forms assigned to adult species is at best a "temporary" ar- the genus Leptocephalus. rangement. As Bohlke and Smith (1968) The pros and cons of describing unidenti- have pointed out, this practice is tantamount 444 BULLETIN OF MARINE SCIENCE, VOL. 28, NO.3, 1978 to deliberately proposing a name which will ultimately fall in synonymy. Since taxono- mists in other fields have long since discon- tinued this practice, it is difficult to defend its continued use in ichthyology. (5) Finally, we can find no reason to treat larval eels any differently than larval fishes of other groups, which are rarely, if ever, described without the benefit of association with known ,. adults. 'll For the purposes of this paper, we follow a middle course. We present the description of one unidentified larva in the hope that .. ,0 other workers may use the description as I '. I "t-'E ~\ supplementary material. We do not, how- \ ever, propose an invalid name for this form, ..• , . ,,\.iF nor do we wish to burden the literature \ .. , . ';,G unnecessarily with code-letters or numbers. ". Instead, we have elected to assign this un- known to a genus, a decision based primarily on similarities between it and known larvae. 35 METHODS ANDSOURCEOF MATERIAL Most leptocephali reported on were col- lected during 2 years of survey work aboard the R. V. DOLPHIN along the continental shelf from Cape Cod, Massachusetts to Palm Beach, Florida. Procedures during the first year are covered in detail in Clark et a1. 35 (1969) and during the second year in Clark ,I iBB et al. (1970). Collecting stations during those i 2 years are shown in Figure 1. Transects ycc with single-letter designations were sampled on eight cruises from December 1965 to De- cember 1966. Transects with double-letter designations were sampled on four seasonal cruises from May 1967 to February 1968. Supplemental, short-term cruises of the R. V. DOLPHIN and R. V. DELAWAREII have also yielded ophichthid larvae. Station locations and hydrographic conditions are contained in Fahay and Obenchain (un pub!.) which is available on request. We began our work on leptocephali by ~ Figure 1. Locations of plankton-collecting sta- tions during two I-year surveys of the R. V. DOLPHIN. FAHAY AND OBENCHAIN: OPHICHTHJD LEPTOCEPHALI 445 analyzing morphometric and meristic char- Cosker (1977) but some were obtained acters in all eel families and later concen- from X-ray analysis of specimens we bor- trating our efforts on the family Ophichthi- rowed from various institutions. Information dae. Our measurements, counts, and terms on preanal vertebrae is meager but counts are follow Eldred (1966) except that we follow included if known.