CASTLE: NOTACANTHIFORMES. ANGUILLIFORMES 

 Table 13. Extended. 



73 



Scrrivo- 

 mcndae 



Anguil- 

 lidac 



Monn- 

 guidac 



Heicrcn- Myrocon- 



chelyidae Muraenidae gndac 



Xenocon- 

 gndae 



Nemich- Sacco- Eury- Mono- 



ihyidae Cyematidae pharyngidae pharyngidae gnathidae 



+ 



+ 



+ 

 + 



+ 

 + 



+ 



+ 



+ 

 + 



+ 



+ 



(+) 

 (+) 



+ 

 + 



+ 

 + 

 + 

 + 

 + 

 + 

 + 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 

 + 



+ 

 + 



+ 

 + 

 + 

 + 

 + 

 + 



+ 

 + 



+ 

 + 

 + 

 + 

 + 

 + 

 + 

 + 

 + 

 + 



+ 

 + 

 + 

 + 

 + 

 + 

 + 

 + 

 + 

 + 



+ 

 + 

 + 

 + 

 + 

 + 

 + 

 + 

 + 



Randall and McCosker (1975) show to have a mean vertebral 

 range of 1 43 in Chile and 1 25 in the Gulf of California. Variation 

 across longitude is apparently not usual but may be consider- 

 able; for example, McCosker (1977, 1979) demonstrates that 

 the ophichthid Myrichlhys maculatus has a mean vertebral count 

 of 153 in the East Pacific to 195 in the Red Sea. 



Two other problems arise in using vertebral/myomere char- 

 acters in matching leptocephali with their adult species. These 

 are the prevalence of damaged tails in adults of some species, 

 especially those that are slender-tailed (Nettastomatidae, some 

 Congridae and Muraenesocidae) and hence the unavailability 

 of vertebral counts; and the overlap or near concordance of 

 vertebral numbers within species groups. For example, in the 

 western Indian Ocean there are 15-20 species of the muraenid 

 genus (iymnolhorax which have vertebral numbers within the 

 range 130-145. Unless other characters (e.g., fin-ray numbers) 

 can be shown to differ significantly between these species, it is 

 likely that their leptocephali, all having rather similar pigmen- 

 tation, will prove difficult, if not impossible, to identify. 



However, there is a reliable correlation between the segmental 

 position of the larval kidney and that of the adult. The larval 

 nephros (opisthonephros) is typically an elongate sac lying above 

 the gut approximately in the middle of the body, i.e., near the 

 anus in those larvae with a relatively short gut (Xenocongridae, 

 Nettastomatidae, Ophichthidae) or some distance in front of it 

 in those having a long gut (Congridae). The segmental position 

 of the kidney changes little, ifat all, during larval life and through 

 metamorphosis into the juvenile. Its position then very ap- 

 proximately agrees with the end of the body cavity and the first 

 caudal vertebra. The correlation in the nephros position has 



been successfully employed as an identification character for the 

 Muraenidae and other families (Blache, 1977) and for some 

 Ophichthidae (Leiby , 1981) but its value has not yet been com- 

 prehensively explored across the Anguilliformes as a whole. 

 Further evidence for the stability of nephros position from larva 

 to adult, at least in the Ophichthidae, is provided in Fig. 33. 

 The figure expresses the mean segmental positions of the end 

 of the nephros in the larvae and adults of various western At- 

 lantic ophichthids of the subfamily Myrophinae and the four 

 tribes of the subfamily Ophichthinae. There is close agreement 

 in position of the nephros between larvae and adults of all 

 species. Furthermore, the position of the kidney (and first caudal 

 vertebra) is conspicuously further back along the body in the 

 tribes Callechelyini and Bascanichthyini. These are readily re- 

 cognisable short-tailed ophichthids whose larvae can be im- 

 mediately identified as such by the posterior position of the 

 nephros. There is considerable overlap in this character between 

 the Myrophinae, Sphagebranchini and Ophichthinae although 

 individually the species are distinct. 



The larval nephros is typically supplied and drained by two 

 prominent blood vessels passing vertically between the lateral 

 muscles to the aorta and cardinal veins below the vertebral 

 column. The segmental position of the last of these vessels in 

 the leptocephalus and its correlation with the position of the 

 first caudal vertebra in the adult has been emphasised in larval 

 identification. However, it seems simpler to use nephros posi- 

 tion instead. 



In those groups of larvae in which the anus does not move 

 forwards during metamorphosis, there is some agreement be- 

 tween number of preanal myomeres and preanal vertebrae. 



