392 
PACIFIC SCIENCE, Vol. XX, October 1966 
Dysommidae: Dysomma anguillare 
Anguillidae: Anguilla rostrata 
Eleterenchelidae : Heterenchelys biaggii 
Moringuidae: Morin gua javanica, M. macrochir 
Xenocongridae: Chilorhinus piatyrhynchus, 
Chlopsis bicolor, Kaupichthys brachychirus, 
K. diodontus 
Dysomminidae: Dysommina rugosa 
Muraenidae: Anarchias cantonensis, A. leu- 
cur us, Channomuraena vittata, Uropterygius 
fuscoguttatus, U. knighti, U. marmoratus, U. 
supraforatus, U. ti grin us, U. xanthopterus, 
Echidna nebulosa, E. polyzona, E. unicolor, 
Enchelycore nigricans, Enchelynassa canina, 
Evenchelys macrurus, Gymnomuraena zebra, 
Gymnothorax eurostus, G. javanicus, G. 
meleagris, G. petelli, Muraena helena, M. 
pardalis, Rabula juscomaculata, Strop hidon 
brummeri 
Serrivomeridae: Serrivomer sector 
Nemichthyidae: Avocettina bower si, Cyema 
atrum, Nemichthys s col op ace us 
RESULTS 
In all of the eels examined, with only one 
exception, the following bones of the gill arch 
skeleton are present: ceratobranchials and epi- 
branchials 1, 2, 3, 4 and the upper and lower 
pharyngeal tooth-bearing dermal bones. Pharyn- 
gobranchial 1 is absent without known excep- 
tion. Other bones of the gill arch skeleton, 
either present or absent, are summarized in 
Table 1, for the species examined and others 
reported in the literature. Information on eel 
gill arches is present in the following papers: 
Asano (1962) ; Beebe (1935^, 1935 b) ; Beebe 
and Crane (1936, 1937^, 1937&) ; Bohlke 
(1957); Castle (1961); Cope (1871, 1884); 
Gill (1890^-0; Gosline (1950, 1951^); Jang 
(1957) ; Jaquet (1920) ; Popta (1904) ; Regan 
(1912 b)\ Takai (1959); Trewavas (1932). 
DISCUSSION 
Eel Lineages 
Cope (1871, 1884) split the eels into two 
orders: one, the Colocephali, included only the 
morays ; the other, the Enchelycephali, included 
the other eels. Cope apparently did not regard 
these two orders as separate lineages. The 
morays he regarded simply as a specialized off- 
shoot of a more generalized stock, of which the 
Anguillidae were examples (Cope, 1884: 584). 
Cope’s two groups were sometimes con- 
sidered by later authors as orders (e.g., Herre, 
1953), as suborders (e.g., Gill, 1890^; Jordan 
and Davis, 1892; Jordan and Evermann, 1896; 
Jordan and Snyder, 1901), or sometimes as 
groups without specific rank (e.g., Fowler, 
1936). 
Regan (1912 b) did not discuss the matter 
of eel lineages as such, but in his key to the 
families he divided the eels into two groups, 
each including several families, depending on 
whether the frontal bones are fused or, alter- 
natively, are separated by a suture. Subsequent 
authors have generally followed Regan, but 
further suggested that his two groups represent 
two primary evolutionary lineages within a 
single order (Gosline, 1951^/304-5; Asano, 
1962:62). 
It is not possible to divide the eels into two 
such groups on the basis of gill arch characters. 
Yet Regan’s groups seem to this author to be 
natural ones and his division of the order is 
used here. It is possible, however, to sub- 
divide one of Regan’s groups, that characterized 
by fused frontal bones, on the basis of gill arch 
characters discussed below. Thus, in the material 
comprising this study three lineages are appar- 
ent: 
1. Anguilloid: Anguillidae, Heterenchelidae, 
Serrivomeridae, Nemichthyidae ( ?) , Morin- 
guidae, Xenocongridae, Dysomminidae, and 
Muraenidae. 
2. Synaphobranchoid : Synaphobranchidae, 
Ilyophidae, Simenchelidae, and Dysommidae. 
3. Congroid: Congridae, Heterocongridae, 
Nessorhamphidae, Nettastomidae, Derichthyi- 
dae, Ophichthidae, and Muraenesocidae. 
During the history of each of these three 
lineages the gill arch skeleton seems to have 
been similarly modified. The modifications have 
involved: (1) progressive enlargement or pro- 
gressive reduction with eventual loss of cer- 
tain skeletal parts, (2) simplification in the 
form of the skeletal parts (loss of grooves and 
processes), (3) an anterior shift in position of 
the lower pharyngeal tooth plates, which gradu- 
