64 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Table 9. Composition, Distribution and Habitat of ihe Anguilliformes. 



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



Synapho- Ophich- Netla- Dench- 



branchi- Dysom- Simcn- thi- Con- Muraenc- stomali- Colo- thyi- Semvo- Anguil- 



dae matidae chelyidae dae gndae socidae dae congndae dae mendae lidae 



Helcr- 

 Monn- enchelyi- 

 guidae dae 



Taxonomic components: 

 Known genera (adults) 

 Known genera (larvae) 

 Known species (adults) 



Distribution: 

 Atlantic: Genera 

 Species 

 E. Pacific: Genera 

 Species 

 I.-W. Pacific: Genera 

 Species 



Habitat (species): 

 Freshwater 

 Shelf: Tropical 



Temperate 

 Slope/abyssal 

 Pelagic 



in determining relationships. Eel species are principally distin- 

 guished externally, by teeth and cephalic pore patterns and by 

 meristics, especially the number of vertebrae. The latter reflects 

 the number of myomeres in the leplocephali. 



Many of the adult characters by which the families and genera 

 differ from one another appear to be correlated with the extent 

 to which the rather sedentary mode of life associated with bur- 

 rowing, crevice-dwelling or pelagic habits has been elaborated 

 throughout the group. In most families of eels there are species 

 in which the body is very slender, with vertebrae numbering 

 180 or more (Table 10). The pectoral fins are reduced or lost 

 variously in families (Muraenidae, Heterenchelyidae), genera 

 (Ophichthidae, Xenocongridae), or even within the life span of 



individuals {Moringita). The median fins may also be reduced 

 to vestiges either in height or in length by a posteriorwards shift 

 of their origin, or they may be entirely lost, though pterygio- 

 phores can be retained. Scales occur only in some of the syna- 

 phobranchoids and in the Anguillidae. 



Other characters are not so clearly associated with the adop- 

 tion of fossorial, cryptic or pelagic habits. These include the 

 ventral displacement of the gill openings (the extreme devel- 

 opment being in some Synaphobranchidae and a few Ophich- 

 thidae where they are confluent ventrally); the ventral displace- 

 ment of the posterior nostril (most Ophichthidae, Xenocongri- 

 dae, to some extent the Synaphobranchidae) so that it may even 

 open within the mouth; or its dorsal displacement (Muraenidae), 



Table 10. Some Morphological Characters of the Anguilliformes. + = All or most species; ( + ) = some species only; * = presumed 



primitive condition. 



