394 
PACIFIC SCIENCE, Vol. XX, October 1966 
TABLE 1 ( Continued ) 
FAMILY AND genus Bl B2 B3 B4 Hi H2 H3 C5 12 13 UP3 UP4 
Heterenchelidae 
Heterenchelys 
O 
o 
c 
C 
Anguillidae 
Anguilla 
O 
o 
- 
c 
Serrivomeridae 
Serri vomer 
o 
c 
- 
c 
*Platuronides 
o 
X 
X 
X 
Nemichthyidae 
Nemichthys 
o 
- 
- 
- 
Avocettina 
c 
- 
- 
- 
*Labichthys 
X 
X 
X 
X 
*Nematoprora 
X 
X 
X 
X 
Cyema 
- 
— 
- 
— 
( Cyema lacks El, E2, 
and E3. E4 
is ossified. 
Moringuidae 
M. javanica 
C 
R 
- 
- 
M. macrochir 
o 
- 
- 
- 
Xenocongridae 
C hlops is, etc. 
- 
- 
- 
- 
K. diodontus 
- 
- 
- 
- 
Dysomminidae 
Dysommina 
- 
- 
- 
Muraenidae 
Anarchias, etc. 
- 
- 
- 
- 
Echidna, etc. 
- 
- 
- 
- 
ally become supported by the fourth rather 
than the fifth ceratobranchials. 
The tendency toward loss of elements has 
been so pronounced that it is possible within 
each lineage to separate primitive from ad- 
vanced forms simply on the basis of the relative 
completeness of the gill arch skeleton, the 
primitive forms having more, the advanced, 
fewer skeletal elements (Table 1). 
Con gr old Lineage 
A rather complete set of gill arches is present 
in most members of this lineage, except for the 
ophichthids. The arches of Conger (Figs. 1,2) 
are perhaps the most generalized. Dorsally, 
epibranchial one (El) bears an anterior, car- 
tilage-capped process, presumably an articular 
surface for, or perhaps a rudiment of, pharyn- 
gobranchial one, which is not present as an 
independent skeletal element among eels. 
Pharyngobranchial two (12) bears a cartilage- 
capped medial process, another primitive fea- 
ture not generally present in eels. 
o 
o 
c 
o 
o 
o 
o 
o 
o 
o 
c 
o 
o 
o 
o 
o 
o 
o 
c 
o 
o 
o 
o 
o 
o 
o 
X 
p 
o 
o 
-O- 
o 
o 
c* 
o 
o 
o 
o 
o 
o 
o 
c* 
o 
c* 
o 
o 
o 
o 
o 
X 
p 
X 
o 
o 
o 
X 
X 
X 
p 
p 
p 
o 
o 
c* 
c* 
c* 
— 
— 
— 
-o- 
o 
o 
c 
o 
o 
o 
o 
o 
o 
o 
c 
o 
o 
o 
o 
o 
o 
o 
_ 
o 
o 
o 
o 
o 
o 
o 
- 
o 
R 
o 
o 
o 
o 
o 
- 
o 
- 
o 
-O- 
o 
o 
_ 
_ 
_ 
o* 
-o- 
- 
- 
- 
- 
- 
o* 
-o- 
The arches of Muraenesox are very similar 
to those of Conger. Those of Gorgasia (Figs. 
3, 4), Ariosoma (Figs. 5, 6), japanoconger, 
and Anago are hardly more specialized. 
Most ophichthids are distinguished in having 
the proximal ends of the dorsal parts of the 
first and second arches connected through a 
continuous cartilage, a peculiarity not present 
in any other of the eel families studied. Among 
generalized ophichthines might be placed those 
eels with a reasonably developed series of basi- 
branchials and an ossified fifth ceratobranchial 
(C5), namely Bascanichthys, Mystriophis, 
Brachysomophis, Ophichthus, and Myrichthys. 
Even in these forms, however, the basibran- 
chials are somewhat reduced (Table 1), and C5 
is in various stages of reduction. 
Bascanichthys (Fig. 7) retains one primitive 
feature not found in the other genera examined, 
the double articulation of C4 with basibranchial 
four (B4). In this genus C5 seems reduced to 
a minute ossicle on the posterior edge of the 
lower pharyngeal tooth plates. 
