Congrid Leptocephali in Australasian Waters with Descriptions of Conger wilsoni (Bl. and Schn.) and C. verreauxi Kaup.
Asano (1962, p. 63) has recently indicated the similarities and differences between the various genera of congrid eels and has distinguished two groups: (a) Subfamily Anagoinae, which includes Anago Jordan and Hubbs, 1925, Ariosoma Swainson, 1838, Alloconger Jordan and Hubbs, 1925, and Chiloconger Myers and Wade, 1941, and (b) Subfamily Congrinae, which includes the other genera of congrid eels. This distinction, based on the morphology of the adults, is also shown by the larvae, as I have already pointed out (Castle, 1963). Genera of the Anagoinae have a leptocephalus which possesses a round eye without a pigment patch below the iris; dorsal and anal fins restricted even in late development to the posterior tip of the body, that is, to the last 10–20 segments; somatic pigment on the lateral surface in the form of a short line of minute, compact chromatophores along each myoseptum below the lateral line; a series of larger, somatic chromatophores on the ventral midline for the anterior third of the intestine; as a closely packed splanchnic series along the upper aspect of the gut from the gall bladder to the vent (along the kidney ducts); and sometimes as a somatic series of chromatophores along the dorsal midline. Leptocephali of genera in the Congrinae have an oval eye with a crescentic patch of pigment below the iris; the dorsal fin originates variably according to the stage of growth but the origin is usually about 30–40 segments in front of the tail tip; somatic pigment in the form of a paired, ventral series of chromatophores as though along the intestine from the pectoral region usually through to the vent; midlateral pigment, if present, in the form of large, diffuse, regular but not segmental spots and sometimes longitudinal rows above and below this. At the present time Asano recognises about eight genera for this stem of the Congridae but as I have shown (1963, p. 17) Rhynchocymba Jordan and Hubbs, 1925, is a synonym of Gnathophis Kaup, 1859, and I believe that Rhynchoconger Jordan and Hubbs, 1925, and Japonoconger Asano, 1958, should be replaced by genera of the Bathycongrus Ogilby, 1898-group. The confusion in these genera cannot easily be resolved through the literature as early descriptions are often inadequate to show even generic distinctions. The general lack of knowledge of adult eels in the Indo-Pacific has been a major difficulty in the detailed study of collections of leptocephali, but an examination of such collections sometimes reveals data helpful in the identification of adults. Over recent years, collections of larvae have been increasing more rapidly than collections of adults, mainly due to the increased development of plankton studies. These collections of leptocephali can now be expected to provide an important adjunct to the development of the systematics of the Apodes.