72 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Table 13. Major Morphological and Pigment Characters of Anguilliform Leptocephali (Families). + = All or most species; ( + ) = some 



species only. 



chias. Uropterygius and to a lesser extent Channotnuraena the 

 dorsal and anal fins are much restricted and distinctive as such 

 early in the euryodontic stage (Table 21 and Fig. 41). At least 

 in the Ophichthidae (Leiby, 1982), even in those species which 

 lack a dorsal fin in the adult, pterygiophores and actinotrichia 

 develop in the larvae. There is also a marked correlation between 

 position of dorsal fin origin in larvae and adults. In the congrid 

 Ariosoma and related genera, the anus is subterminal and the 

 dorsal and anal are also restricted but develop progressively 

 forwards during late larval growth (Table 17 and Fig. 37). Dorsal 

 fin-rays range in number from 1 10 in Neocyema erythrosoma 

 to 600-700 in some ophichthids, anal rays usually being some- 

 what fewer. The large number and apparent considerable vari- 

 ability of median fin rays in most eels has resulted in this meristic 

 character being neglected, but it may be of considerable use in 

 larval identification (Leiby, 1981). 



The caudal fin develops at least as early as the anal, its sup- 

 porting structure being 3 hypurals, the first two joined distally, 

 enclosing a foramen. Typically hypurals 1 and 2 support 4 rays, 

 hypural 3 supports 5 rays, but the hypurals are much broader 

 in the Synaphobranchoidea, supporting about 16 rays. The fin 

 is resorbed, the rays shorten, and finally become embedded in 

 the tail tip of heterocongrin and many ophichthid larvae shortly 

 before metamorphosis. 



Myomeres differentiate during embryonic development but 

 because of their relatively high number and small size it is not 

 known for any species whether the definitive number of the 

 adult is established then, or after hatching. However, differen- 

 tiation of the most posterior myomeres, as evidenced visually, 

 appears to occur during the engyodontic stage, even for species 



with very high total numbers of myomeres. Total counts for 

 species with more than about 180 are difficult to make accu- 

 rately, even in fully grown leptocephali. Myomeres are less readily 

 counted as body transparency is lost at metamorphosis. The 

 range in myomere number across the Anguilliformes is 74-78 

 in the short-bodied Cyema atrum to more than 400 in the greatly 

 elongate Neinichthys scolopaceus (Table 10) with ranges for 

 species of about 10 myomeres at the lower end (e.g.. for Anguilla, 

 Jespersen, 1942) to about 30 in the range 200-300 (e.g., for 

 Nettastomatidae, Smith and Castle, 1982). 



Vertebrae first begin to differentiate posteriorly just before 

 metamorphosis with the constriction of the terminal portion of 

 the notochord proceeding anteriorly. 



The value of vertebral counts in defining eel species has be- 

 come firmly established in eel studies (Bohlke, 1978). The cor- 

 relation of vertebral number with number of myomeres in larvae 

 was demonstrated by Jespersen (1942) for Angidlla and taken 

 upextensively in recent years (Blache, 1977; Smith, 1979; Smith 

 and Castle, 1982). In utilizing this agreement between larvae 

 and adults, associated phenomena need to be further explored 

 and assessed, e.g.. pleomerism (the correlation in related species 

 of vertebral number and maximum body length attained: Lind- 

 sey, 1975), "Jordan's Rule" (the tendency for fishes in polar or 

 cool waters to have more vertebrae or other meristic parts than 

 have related forms in tropical warm waters, Jordan. 1892), and 

 sexual dimorphism in vertebral number (as occurs in Aforingua 

 edwardsi. Castle and Bohlke. 1976). 



The existence of latitudinal dines in vertebral number in eels 

 has been proposed, but not convincingly demonstrated, except 

 possibly for the muraenid Gymnothorax panamensis which 



