Gill Arches of Teleostean Fishes — Nelson 
405 
sonal observations). Perhaps the tendency 
toward the reduction of these processes may 
be evidence of genetic relationship. 
SUMMARY 
1. On the basis of gill arch and other 
characters the eels may be divided into at least 
three evolutionary lineages: anguilloid (An- 
guillidae, Fleterenchelidae, Serrivomeridae, 
Nemichthyidae( ?), Moringuidae, Xenocon- 
gridae, Dysomminidae, Muraenidae), synapho- 
branchoid (Synaphobranchidae, Ilyophidae, 
Simenchelidae, Dysommidae), and congroid 
(Congridae, Heterocongridae, Nessorhamphi- 
dae, Nettastomidae, Derichthyidae, Ophichthi- 
dae, Muraenesocidae) . 
2. In each of these lineages the gill arches 
seem to have been similarly modified through 
(a) the progressive enlargement, or reduction 
with eventual loss, of skeletal parts, (b) sim- 
plification in form of the skeletal parts (loss of 
grooves and processes), (c) an anterior shift 
in position of the lower pharyngeal tooth plates, 
which gradually become supported by the fourth 
rather than fifth ceratobranchials. 
3. Within the anguilloid lineage the Heter- 
enchelidae and Anguillidae are the most gener- 
alized in gill arch structure. Moringua is some- 
what more specialized. The Xenocongridae, 
Dysommina, and Muraenidae resemble one 
another more than they do other members of 
this lineage. The Muraenidae have the gill 
arches most highly specialized, and on the basis 
2.0 
1.5 
O ANGUILLIDAE 
® MORINGUIDAE 
® MURAENIDAE 
© XENOCONGRIDAE 
□ CONGRIDAE 
Eg) HETEROCONGRIDAE 
® MURAENESOCIDAE 
A OPHICHTHIDAE, ECHELINAE 
S) OPHICHTHIDAE, OPHICHTHINAE 
® SIMENCHELIDAE 
D SYNAPHOBRANCHIDAE 
SB 
SI 
SI 
m 
m 
si 
si 
si 
S) SI 
s 
□ 
□ 
□ 
□ 
□ 
I0.8 
1.2 
DISPLACEMENT 
Fig. 58. Scatter diagram showing correlation between body elongation and posterior displacement of the 
branchial region in selected representatives of some eel families. Elongation = log body length/maximum 
body diameter. Displacement — log 10 X postcranial head length/cranial length. Example: for Moringua 
javanica the following measurements were taken: total length 805 mm, maximum body diameter 11 mm, 
head 49 mm, cranium (snout tip to posterior limit of cranium) 17 mm. 
Elongation = log 805/11 = 1.86 
Displacement = log 320/17 = 1.27 
Measurement data on other species will be furnished by the author on request. 
