100 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 5 1 . Leptocephali of (A) Callechelys sp.; (B) Catesbya pseudomuraena, and (C) Kaupichlhys hypoproproides. 



50, top). Notacanthiforms have no true caudal fin. In adult 

 notacanthiforms the vertebrae approaching the tip of the tail 

 become progressively less ossified, the centra being reduced to 

 rings around the notochord separated from the neural and hemal 

 arches. Finally the vertebrae disappear, leaving the notochord 

 freely exposed (McDowell, 1973). There is no hypural structure, 

 and caudal fin rays, if they exist, are indistinguishable from the 

 posterior anal fin rays. The notacanthiform larva likewise has 

 no caudal fin (Fig. 50, bottom); the notochord ends freely, but 

 there are two structures that may be hypural elements. Posterior 

 to these and to the notochord is a single filament that trails 

 freely for a variable distance and might represent a caudal fin 

 ray. The anal fin occupies the short space between the anus and 

 the end of the tail proper (excluding the caudal filament). The 

 important point here is that lumping notacanthiform and an- 

 guilliform larvae as pointed-tail leptocephali is unwarranted, 

 because the caudal structure is quite different in the two groups. 

 Returning to the diagram in Fig. 49, the fork-tailed leptocephali 

 can be viewed as the primitive type of leptocephalus present in 

 the elopid and megalopid branches and retained in the Albulidae 

 as well. Two pomts of transformation occur, one in the nota- 

 canthiform line and one in the anguilliform line. The modifi- 

 cations in each reflect modifications in the adults and by them- 

 selves are not indications of a special relationship. Additional 

 leptocephali illustrations were prepared and are presented here 

 without further comment (Figs. 51, 52). 



Relationships between Elopomorphs 



AND OTHER TeLEOSTS 



A widely favored view today is that the teleosts consist of 

 four major groups in a cladistic sense: the Osteoglossomorpha, 

 Elopomorpha, Clupeomorpha, and Euteleostei (Greenwood et 

 al., 1966; Greenwood, 1973; Nelson, 1973; Patterson and Ro- 

 sen, 1977). These groups are arranged in a hierarchy with the 

 Osteoglossomorpha as the sister group of the remaining three, 

 the Elopomorpha as the sister group of the remaining two, and 

 the Clupeomorpha as the sister group of the Euteleostei (Fig. 

 53). This classification is based on a few characters that are 

 thought to represent synapomorphies. It is essential, therefore, 

 to evaluate these characters carefully, because the whole clas- 

 sification stands or falls on their reliability. 



The Elopomorpha is united by three characters: I ) the pres- 

 ence of rostral and prenasal ossicles; 2) the initial fusion of the 

 angular and retroarticular bones in the lower jaw; 3) the presence 

 of a leptocephalus larva. It is not certain that eels have rostral 

 ossicles. Considering the extreme fusion that has taken place in 

 the anterior extremity of the skull in eels, it should not be 

 surprising if the rostral ossicles were lost as well. Still, it means 

 that the character may not be wholly inclusive of the group. The 

 second character, the fusion of the angular and retroarticular, 

 seems to hold for eels (Leiby, 1979b) and appears to be a true 

 synapomorphy. That leaves the leptocephalus, and its role is 



