468 
PACIFIC SCIENCE, Vol. XXII, October 1968 
0.5 cm 
Fig. 3. Telsons of female (A) and male (jB) Gonodactylus falcatus from Hawaii, sc, Submedian carinae; 
ic, intermediate carinae; Ic, lateral carinae; cc, central carinae; It, lateral teeth; it, intermediate teeth; at, acces- 
sory teeth; st, submedian teeth. 
Although the specimens from the Philippines 
that were examined had narrow carinae, indi- 
viduals with more rounded carinae also occur 
in the same area. Kemp (1915) stated that the 
majority of specimens from Bantayan, Puerto 
Galera, and Taytay in the Philippines belongs 
to "form B” which corresponds to Borradaile’s 
var. rotundus (probably Serene’s ternatensis ) , 
while one specimen is the narrow keeled type 
"form A” (= var. ternatensis deMan). 
sexual dimorphism ; Sexual dimorphism has 
been noted in G. falcatus by Bigelow (1931) 
and Serene (1954). The sexes are quite dis- 
tinct in Hawaiian specimens. The females (Fig. 
3 A) have the carinae of the sixth abdominal 
somite and telson narrower and more sharply 
defined than those of males of corresponding 
size (Fig. 3 B). However, as Serene has noted, 
this inflatedness and rounding of carinae and 
telson teeth increases with age, so care must be 
taken to insure that equal-sized specimens are 
being compared. The dimorphism of the dactyli 
is also pronounced in the Hawaiian population, 
with the females having the swelling of the base 
of the dactylus making a sharp angle with the 
shaft (Fig. 4A), while in the males the angle is 
less distinct (Fig. 4B) ; furthermore the tip of 
the dactylus of the females is sharply recurved, 
while that of the males is not. This dimorphism 
is developed at a small size in the Hawaiian 
population. The dactyli of a 43 -mm male from 
the Philippines were indistinguishable from 
those of females from the same area, while in 
the Hawaiian collections specimens as small as 
17 mm could be sexed by inspecting the dactylus. 
Fig. 4. Dactyli of female (A) and male (B) Gonodactylus falcatus showing sexual dimorphism. 
