200 
PACIFIC SCIENCE, Vol. XVIII, April 1964 
acuticeps well apart and make it more confi- 
dently identifiable than are most other described 
leptocephali. 
Two larvae from the eastern tropical Pacific 
in the Scripps Institution fish collection appear 
to be the first new material on L. acuticeps to be 
reported since the original specimen. They share 
the general format and the determinable visceral 
and pigmentation characters of the original 
specimen, and differ in details that apparently 
represent growth-stage differences and individ- 
ual or population variation. 
For unspecified reasons, D’Ancona (1928) 
and Bertin (1936) assigned L. acuticeps to the 
Congridae, but the studies reported in the pres- 
ent paper show that in both morphological and 
color-pattern characters acuticeps most closely 
resembles the larvae of Nemichthys, the type 
genus of the Nemichthyidae. The larva of Ne- 
michthys differs from more conventional lep- 
tocephali in its greatly attenuated shape, very 
high somite count, and apparent continuous, 
life-long addition of new somites in its thin, 
filament-like tail tip. However, a detailed com- 
parison of the Nemichthys larva with Lepto- 
cephalus acuticeps shows that these outwardly 
conspicuous differences mask fundamental re- 
semblances in both morphological and color- 
pattern characters, and that the larva of Nemich- 
thys is, essentially, an exaggerated acuticeps. 
The most significant of the pigment characters 
that they share is an internal three-spot pattern 
(visible through the transparent somites) that 
is not known to occur in any other leptocephali. 
These spots are in the anterior half of the body, 
occupying the level between the midlateral axis 
and the lower edge of the somites. Each spot 
consists of several small melanophores loosely 
grouped together in a more or less linear cluster, 
situated on the median connective tissue that is 
compressed between the right and left muscle 
layers. The spots are substantially farther back 
in Nemichthys larvae than in L. acuticeps , in 
relation to somite numbers. In both kinds of 
larvae, however, the first spot is above or slightly 
behind the pylorus, near or overlapping a ver- 
tical artery; the second spot is about 10-12 
somites ahead of the posterior end of the kidney, 
adjacent to or overlapping the last vertical 
artery anterior to the main renal artery; and 
the third spot is about 24-31 somites behind 
the posterior end of the kidney. The anatomical 
significance of this third location is not clear 
from the present data. The predictable relation- 
ship between the internal three-spot pattern 
and the visceral anatomy suggests that these 
color-pattern and structural characters have op- 
erated as a very stable unit during phyletic 
changes. 
Although metamorphosing specimens are still 
lacking, the available evidence places Lepto- 
cephalus acuticeps in the Avocettina section of 
the family Nemichthyidae. From the known 
adult characters of Nemichthys and Avocettina, 
one can predict that their larvae must differ 
in somite and tail-tip characters in precisely the 
way that L. acuticeps differs from larvae of 
Nemichthys. On present knowledge, acuticeps 
cannot be restricted to any single species, and it 
is probable that all species in the Avocettina 
group (including Labichthys and, tentatively, 
Avocettinops ) have larvae of this general type. 
Thus, it seems best to treat acuticeps compre- 
hensively as an informal group category that 
designates the kind of larva that characterizes 
the avocettinas as a whole. A more detailed 
understanding of differentiation in larval popu- 
lations within the acuticeps complex must await 
not only the study of larger series of larvae but 
also a world-wide revisionary study of the adult 
avocettinas. 
REFERENCES 
Asano, H. 1962. Studies on the congrid eels 
of Japan. Bull. Misaki Mar. Biol. Inst. Kyoto 
Univ. No. 1:1-142, figs. 1-62. 
BAUCHOT, M. L. 1959. Etude des larves lepto- 
cephales du groupe Leptocephalus lanceolatus 
Stromman et identification a la famille Ser- 
rivomeridae. Dana Rept. No. 48:1-148, pis. 
1-2, figs. 1-105. 
Beebe, W., and J. Crane. 1936. Deep-sea fishes 
of the Bermuda oceanographic expeditions. 
No. 3. Family Serrivomeridae. Zoologica 20: 
53-102, figs. 23-42. 
