62 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



behind it, by a distance not exceeding the length of the anal fin 

 base. Flops and Mega/ops leptocephali have lateral pigment but 

 Albula and Pterothrissus leptocephali do not have lateral pig- 

 ment. Elops is distinguished from Mega/ops by having a de- 

 pressed head, more dorsal than anal rays and the origin of the 

 anal fin is under the posterior end of the dorsal fin or slightly 

 behind it. Megalops does not have a depressed head, has fevk'er 

 dorsal rays than anal rays and the origin of the anal fin is under 

 the middle of the dorsal fin. Albula leptocephali are separable 

 from Pterothrissus leptocephali by the distance between the pos- 

 terior edge of the dorsal fin and the origin of the anal fin. In 



Albula this distance is about 2.5 times the length of the dorsal 

 fin base and in Pterothrissus this distance is about 6-7 times 

 the length of the dorsal fin base. Also the snout is short in Albula 

 and prolonged in Pterothrissus. Within genera, meristic char- 

 acters are useful in identification of the species (Table 7). 



The interrelationships of the elopiform fishes are discussed 

 by Smith in a subsequent paper in this volume. 



National Marine Fisheries Service, Southeast Fisheries 

 Center, 75 Virginia Beach Drive, Miami, Florida 33149. 



Notacanthiformes and Anguilliformes: Development 

 P. H. J. Castle 



THE Notacanthiformes (spiny eels) and Anguilliformes (true 

 eels) were united with the Elopiformes (tenpounders, tar- 

 pons, bonefishes) by Greenwood et al. (1966) as the superorder 

 Elopomorpha. These authors noted that members of the three 

 orders share osteological similarities, swim bladder not con- 

 nected with ear (except for Megalops), and a distinctive larval 

 phase (leptocephalus). More recent authors (Nelson, 1973; Fo- 

 rey, 1973b; Patterson and Rosen, 1977) recognised this rela- 

 tionship, though not precisely in this form. There seems little 

 doubt that they are indeed closely related, but in being exclu- 

 sively elongate fishes the notacanths and eels are readily distin- 

 guished externally from the short-bodied, herring-like Elopi- 

 formes. 



NOTACANTI form ES 



McDowell (1973) reviewed the notacanths, a morphologically 

 discrete group of fishes, found on or near the bottom on the 

 deeper continental slope into the deep sea, recognising 2 sub- 

 orders, 3 families, 6 genera and 22 extant species (Table 8). He 

 chose to give subordinal distinction to the Halosauridae on the 

 one hand, and the Notacanthidae and Lipogenyidae jointly on 

 the other, although Marshall (1962) had already demonstrated 

 major structural similarities between these families. 



The Notacanthiformes have in common with the Anguilli- 

 formes a leptocephalus phase, an elongate body form, the as- 

 sociated lengthening of the anal fin, and a reduced caudal fin. 

 Members of the two orders are otherwise dissimilar. Notacanths 

 have well developed pelvic fins; a compact, dorsal fin with spines 

 in some species; scales present and prominent in some; and a 

 large gill opening and opercular flap. Eels lack pelvic fins; the 

 dorsal, unless secondarily reduced or lost, is always long and is 

 supported by delicate rays; scales, if present, are greatly reduced; 

 and the gill opening and its supporting structures are also re- 

 duced. Furthermore, notacanth leptocephali are as distinctive 

 from those of the true eels as are their adults (Fig. 29). They are 

 greatly elongate (up to 180 cm), having a thin post-caudal fil- 

 ament in place of a normal caudal fin; dorsal and pelvic fins are 

 represented by compact, short-based structures present at some 

 stage of larval growth; there is a minute pectoral, straight gut, 

 subterminal anus and the myomeres are V-shaped, not W-shaped; 



pigment occurs in a ventral series and (rarely) below the mid- 

 lateral level. 



Several quite different notacanth leptocephali of this type are 

 known, some almost certainly halosaurids ( Tiluropsis. Lepto- 

 cephalus attcnuatus), some possibly notacanthids (Tilurus) and 

 others of unknown identity (Leptocephalus giganteus). Eggs and 

 early larvae have not yet been identified and information on 

 vertebral numbers is mostly lacking for the group. Until con- 

 firmed identifications have been made and more information 

 is forthcoming from leptocephali, ontogeny is unlikely to con- 

 tribute further to the little that is known of relationships in this 

 order. 



Anguilliformes 



The Anguilliformes make up a much larger and more diverse 

 assemblage. I recognize 21 families. 153 genera and 720 species 

 for the group (Table 9). 



Within the Anguilliformes itself Bohike (1966) reviewed the 



Table 8. Composition, Distribution and Habitat of the Nota- 

 canthiformes. + = All or most species; ( + ) = some species only. 



