PACIFIC SCIENCE, Vol. XVIII, April 1964 
190 
whether they seem to extend completely to the 
ventral margin of the musculature. 
The total length of the original specimen of L. 
acuticeps was 47 mm. The maximum height was 
about 8.5% of the total length. The dorsal pro- 
file of the head was markedly concave; the jaws 
bore about seven upper and six lower teeth on 
each side; Regan’s illustration shows sufficient 
space behind these for the addition of more, 
perhaps smaller, teeth during larval growth. The 
tip of the lower jaw protruded slightly. The 
somites totalled 207, of which 174 (84%) were 
preanal and 33 were postanal. The gut was a 
long, straight, simple tube, with no apparent 
specializations. An enlargement of the liver oc- 
curred at about the 30th somite (hence, the 30th 
somite can be considered the approximate loca- 
tion of the pylorus ) . There were major vertical 
blood vessels anteriorly at somites 16 and 27, 
and farther back at somites 61, 71, and 76. The 
kidney terminated at about the 76th somite, and 
there were therefore about 46 somites between 
the pylorus and the posterior end of the kidney, 
and about 100 between the latter position and 
the anus. Although Regan did not describe the 
tail, his illustration shows that the fleshy part 
was obtusely rounded, with a distinctly rayed 
tip. Bertin mentioned that the hypurals were 
scarcely visible and that the caudal was pointed. 
The vague definition of these characters cer- 
tainly stems at least partly from the relatively 
young stage of the specimen. The known pig- 
mentation of this original specimen included 
an internal row of minute, densely spaced mel- 
anophores along the top of the spinal cord, a 
similar row along the top of the gut beginning 
at about the 30th somite (probably at or near 
the pylorus ) and extending to the anus, and an- 
other row ( probably external ) along the ventral 
surface from the heart region to at least the 
pyloric region. The sides of the tail bore a few 
small scattered melanophores, both above and 
below the level of the notochord. There were 
three internal spots visible through the lower 
halves of the somites, each spot composed of a 
loosely clustered, roughly linear group of small 
melanophores. The first spot was at somites 
27-30, the second at somites 61-62, and the 
third at somites 104-107. The first and second 
spots were each near a major vertical blood 
vessel. 
The two eastern Pacific larvae described in 
the present paper match the determinable char- 
acters of Regan’s Atlantic larva of L. acuticeps 
so closely that there is no doubt of their close 
relationship to it, and therefore I have assigned 
them to acuticeps. So far as known, they differ 
from the Atlantic specimen only in details of 
the sort that are readily subject to variation 
among very closely related larvae or between 
growth stages of a single form. The Scripps spe- 
cimens share the general format and visceral 
characters of acuticeps , but they are much larger 
and have about twice as many teeth, the head 
profile is straighter, and the tips of the jaws are 
even. The Scripps larvae have somewhat lower 
somite counts and the preanal somites constitute 
a slightly higher percentage of the total number. 
In addition, the pylorus is about five somites 
farther forward in the Scripps larvae than its 
estimated position in the original acuticeps, the 
posterior end of the kidney and the main renal 
blood vessels are about 12-14 somites farther 
forward, and there are about 10 or 11 fewer 
50 58 61 63 
Fig. 4. Leptocephalus acuticeps. Section between 
somites 50 and 63 of the 107-mm larva. Numbers 
designate somites. Somite 50 includes origin of vertical 
artery at anterior limit of the cluster of melanophores 
that comprises the second of the three internal spots; 
somite 58 includes origin of main renal artery; somite 
61 marks posterior limit of kidney; somite 63 includes 
origin of renal portal vein. 
