Branchial Muscles in Representatives of Five Eel Families 1, 2 
Gareth J. Nelson 1 2 3 
During the evolution of eels the gill arch 
skeleton of some forms was profoundly modi- 
fied in gross structure. The modifications are 
adaptive and are associated with body form and 
feeding habits of eels (Nelson, 1966). The 
present paper deals with the musculature at- 
tached to the gill arch skeleton of eels repre- 
senting five families, primarily of the suborder 
Anguilloidei. Six genera were chosen for study: 
Conger (Congridae), Anguilla (Anguillidae) , 
Morin gu a (Moringuidae) , Kaupichthys (Xeno- 
congridae), Uropterygius , and Gymnothorax 
(Muraenidae) . The gill arch skeleton of these 
forms shows a progressive reduction of ele- 
ments, showing probable stages in the evolu- 
tionary development of the specialized "pha- 
ryngeal jaws” of the morays — eels of the 
family Muraenidae. 
Gill arch musculature in eels has been studied 
previously only in Anguilla by Dietz (1912) 
and again by Kesteven (1943). Muscle ter- 
minology in the present work follows Vetter 
(1878) and Edgeworth (1935) as far as pos- 
sible. Names of gill arch elements are ab- 
breviated as follows: B, basibranchial; H, 
hypobranchial; C, ceratobranchial; E, epi- 
branchial; I, infrapharyngobranchial; LP, 
lower pharyngeal tooth plate; UP, upper 
pharyngeal tooth plate. Gill arches in eels are 
discussed in detail elsewhere (Nelson, 1966). 
MATERIAL AND METHODS 
Muscles were dissected in preserved adult 
specimens and illustrated for Conger mar- 
gin at us, Anguilla ro strata, Morin gua javanica, 
Kaupichthys diodontus, Uropterygius knighti, 
and Gymnothorax petelli. Observations on re- 
1 This paper is part of a thesis submitted to the 
Graduate Division of the University of Hawaii in 
partial fulfillment of the requirements for the degree 
of Doctor of Philosophy in Zoology. 
2 Contribution No. 261, Hawaii Institute of Ma- 
rine Biology. Manuscript received May 6, 1966. 
3 Present address: Department of Ichthyology, 
American Museum of Natural History, New York. 
lated genera (those listed in Nelson, 1966) 
suggested that the six genera selected for study 
are representative of the families or subfamilies 
to which they belong. All material was ob- 
tained from the collections of the Department 
of Zoology, University of Hawaii. With the 
exception of specimens of Anguilla, study 
material originally was collected by means of 
shallow water rotenone poisoning around Oahu 
and Christmas Island. 
The illustrations show the muscles in ap- 
proximately their relative size and positions. 
Muscles attaching to structures other than gill 
arches are shown transected. Occasionally 
other muscles are shown with parts removed 
to reveal underlying structures. Roots of the 
branchial arteries are included in the illustra- 
tions, for they serve as convenient landmarks, 
separating adjacent muscles. Bertmar (1962) 
and Petukat (1965) have dealt with the on- 
togeny and comparative anatomy of these ves- 
sels in some other teleostean fishes. 
RESULTS 
Conger 
Ventral muscles are shown in Figure 1 and 
listed in Table 1. Obliqui (01-3) occur on 
arches 1-3, extending between cerato- and 
hypobranchials. 03 has its insertion apparently 
transferred anteriorly to H2. A rectus (R4) 
is present only between arches 3-4, extending 
between the proximal ends of C4 and H3. It 
probably represents part of the oblique of arch 
4 with the insertion anteriorly transferred to 
H3. A rectus communis (RC) extends from 
the proximal end of C4, with some of its fi- 
bers inserting on H3, others on H2 in common 
with 03. An anterior trans versus (AT) ex- 
tends between the proximal ends of C4 of 
either side. Extending posteriorly from C5, a 
single pharyngo-clavicularis (PC) attaches to 
the cleithrum. A posterior transversus (PT) 
extends between the distal ends of C5 of either 
side. An adductor (A5) joins the distal ends 
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