Gill Arches of Teleostean Fishes — Nelson 
403 
others separate. The consensus seems to favor 
the view that the group is a natural one. The 
dorsal parts of the gill arches in Nemichthys 
bear some resemblance to those of Serrivomer, 
whereas the ventral parts in Nemichthys are 
somewhat more reduced, paralleling perhaps 
the trend toward reduction in other eel groups. 
Thus, gill arch structure may be consistent 
with the opinion that these two families are 
closely related, but can neither confirm nor 
refute this opinion. In any event, the Nemich- 
thyidae is here included in the anguilloid line- 
age for want of clear evidence to the contrary. 
Functional Significance of Gill Arch Modifica- 
tions in Eels 
Much could be said concerning the functional 
significance of the various types of gill appara- 
tus found among the eels. The following re- 
marks concern one possible interpretation of 
some of those of the anguilloid lineage. 
In generalized teleosts, the cranium, jaws, 
and gill arches form closely integrated parts 
of a mechanical system functioning to seize 
prey organisms. The functional roles of the 
parts of this system have been analyzed by 
several authors (Hdller, 1935; Hofer, 1945; 
Tchernavin, 1947, 1953; Kirchhoff, 1958; 
Kampf, 1961; and others). The functional in- 
terdependence of these parts is dependent on 
their near relative positions. In such generalized 
teleosts as Elops and Epinephelus, the gill arches 
are located close behind the jaws, more or less 
beneath the posterior part of the cranium (Figs. 
51, 52). 
In the eels, however, the arches are pos- 
teriorly displaced from a position beneath the 
cranium to a position behind it. This displace- 
ment is slight in Conger , moderate in Anguilla 
and Chilorhinus, and extreme in Gymnothorax 
and Moringua (Figs. 53-57). 
Probably as a result of this displacement, 
both the pectoral girdle and the gill arches lost 
the attachments to the cranium characteristically 
present in other teleosts. In the case of the gill 
arches, this attachment occurs through the first 
pharyngobranchial. In the case of the pectoral 
girdle, it is through the posttemporal. Both of 
these bones are absent without known excep- 
tions among the eels. 
It seems likely that the position of the gills 
Figs. 51 and 52. 51, Position of branchial region 
in relation to cranium and jaws of Elops hawaiiensis. 
"Branchial region’’ denotes that space bounded ante- 
riorly by the dorsal and ventral proximal ends of the 
first arch, posteriorly by the rear border of the dermal 
tooth plates. 52, Epinephelus juscoguttatus. 
is not without some functional significance. The 
habits of eels, of wedging themselves through 
crevices or burrowing in the sand, seemingly 
require an eel-like body, long and narrow, espe- 
cially in front. Reduction in head diameter 
seems to have been achieved in part by the 
movement posteriorly of the gill arches from a 
position beneath the cranium to one behind it. 
In this connection, the degree of elongation — 
the relation between body length and diameter 
— seems to be correlated with the posterior dis- 
placement of the gill region (Fig. 58). 
With the arches posteriorly displaced, they 
tend to lose their role in seizing prey, which 
then is left to the jaws and cranium alone. This 
loss in function perhaps may account for the 
obvious trend toward the loss of certain gill arch 
elements among eels. This entails the loss of 
firm interconnections between the gill skeleton 
and the cranium, between successive arches of 
the gill skeleton, and between the paired ele- 
ments of either side. Each of these losses tends 
