404 
PACIFIC SCIENCE, Vol. XX, October 1966 
Figs. 53 - 57 . 53, Conger marginatus. 54, An- 
guilla ro strata. 55, Chilorhinus platyrhynchus. 56, 
Gymnothorax eurostus. 57, Morin gua javanica. 
to augment the expansibility of the pharynx, 
which is of obvious significance to an eel-like 
fish. Interestingly, many of these same modifica- 
tions have occurred independently among 
syngnathiform fishes (Jungerson, 1910; 
Rauther, 1925) and symbranchiform fishes (per- 
sonal observation), possibly also as a result of 
spatial separation of jaws and gill arches. 
The functional significance of the so-called 
pharyngeal jaws of the morays and other forms 
remains to be commented on. On the basis of 
the nature of the teeth and the branchial 
musculature, which is to be discussed elsewhere 
(Nelson, MS), these prominent tooth-bearing 
bones apparently function in moving food from 
the jaws into the esophagus. They have devel- 
oped, it seems, in relation to mechanical prob- 
blems involved in moving relatively large food 
organisms through a secondarily elongate 
pharynx. 
Remarks on Eel Origins 
For several reasons, eels are customarily 
regarded as isospondylous derivatives, and, be- 
cause of larval features, as being particularly 
close to the elopoids. Some gill arch characters 
of eels also suggest an isospondylous origin: 
(1) pharyngeal tooth plates are generally not 
fused with underlying endochondral bones, 
(2) the lower pharyngeal tooth plates are some- 
times multiple, (3) retractor ossium pharyn- 
gealium muscles are without an attachment to 
the vertebral column except among some murae- 
nids (Nelson, MS). 
Among teleosts above the isospondylous 
level, pharyngeal tooth plates are generally 
fused with their endoskeletal supports, and the 
lower ones are in a single pair (Nelson, MS) . 
Retractor muscles with an attachment to the 
vertebral column probably are present in all 
forms above the isospondylous level (Dietz, 
1912, 1914, 1921; Holstvoogd, I960, 1965). 
One striking difference between the arches of 
isospondylous fishes and eels is that in most 
of the former prominent tooth plates overlie 
the basibranchials, while no such plates are 
present in any of the eels examined. These, 
however, may be presumed to have been lost in 
relation to the posterior displacement of the 
arches. 
In view of this peculiarity of the gill arch 
skeleton in eels, no striking resemblance be- 
tween it and that of any of the major groups 
of isospondylous fishes can be demonstrated. 
One feature, however, may deserve mention. 
This concerns the loss of medial processes on 
the pharyngobranchials of eels. These processes 
are important supports for the upper pharyn- 
geal bones in most teleosts (Nelson, MS). 
They are absent, however, on the third pharyn- 
gobranchial of Albula among elopoids (but not 
of Megalops, Elops, or Pterothrissus ) , and in 
at least Aldrovandia among halosaurids (per- 
