Observations on Copulation in the New Zealand Grapsid Crab 
Hemigrapsus crenulatus (M.Edw.) 
John C. Yaldwyn 1 
Knudsen in this journal (1964^:9, et seq.), 
and elsewhere (1964&), recently summarized 
existing knowledge of copulation and sperm 
transfer in the brachyuran crabs. In brief, he 
was able to generalize from the few published 
records that in cancroid crabs (Xanthidae and 
Cancridae) there could be elaborate courtship 
prior to the female moult, copulation occurred 
while the female was in the soft-shell condition, 
and the typical position was male-over-female. 
In grapsid and majid crabs, however, there ap- 
peared to be little or no courtship, copulation 
occurred while the female was in the hard-shell 
condition (in the only record of the majid 
Pugettia producta the female was even ovi- 
gerous), and in contrast to the cancroids the 
typical position was female-over-male. 
The first record of copulation in the wide- 
spread family Grapsidae was that of Hiatt 
(1948) for the northern Pacific, American, and 
Asiatic species, Pachygrapsus crassipes Randall. 
Additional details for this species are given by 
Bovbjerg (I960). He describes a limited 
amount of precopulatory courtship as an exten- 
sion to Hiatt’s data. The only other records in 
this family appear to be those of Knudsen 
(1964^) for the North American West Coast 
species Hemigrapsus nudus (Dana) and H. 
oregonensis (Dana). Following Knudsen’s plea 
(1964A41) for further detailed observations 
on brachyuran copulation, these notes on the 
New Zealand species, Hemigrapsus crenulatus 
(H. Milne Edwards), are presented as a partial 
description of mating in this southern shore 
crab. 
H. crenulatus is a common, medium-sized 
grapsid of intertidal mud flats and similar pro- 
tected environments in New Zealand (see Ben- 
nett, 1964:81 and Dell, 1963:54), and also 
occurs in similar habitats in southern Chile 
(Garth, 1957:97). The following notes were 
1 Australian Museum, College St, Sydney, N.S.W. 
Manuscript received February 19, 1965. 
made by the author during field work in 1954 
on the extensive intertidal flats to the east of the 
Hutt River mouth, Wellington Harbour, in an 
area now completely "reclaimed” and developed 
for industrial building. 
On 11 September 1954, Hemigrapsus crenu- 
latus was found to be common under pieces of 
wood and among algae and shells on intertidal 
flats at the mouth of the Hutt River. Several 
specimens, including ovigerous females, were 
brought to the laboratory for observation. After 
being confined together in a collecting jar for 
some hours, two specimens were seen to be in 
copulation. The jar was dry, as the water they 
had been in for some time had just been dis- 
carded. 
The female was slightly smaller than the 
male, and ventral surface was placed to ventral 
surface. The female was slightly more posterior 
than the male. The latter enclosed the female 
within its walking legs, which were right around 
those of the female and on to the dorsal surface 
of her carapace. The female’s legs were stretched 
out laterally, not attempting to grip the male. 
The male’s chelipeds were held out aggressively 
over the anterior part of the carapace of the 
female. The latter’s chelipeds were folded 
under her. The female abdomen was opened 
right back and the extreme end was hooked on 
to the posterior edge of the male carapace. When 
I looked between them, the male abdomen ap- 
peared to be opened out, as I could see an open 
groove. (I did not observe the position of the 
pleopods.) The mouthparts of the male were 
working rapidly. The pair remained as described 
for about 10 minutes; they could move which- 
ever way up they were, and they were con- 
siderably disturbed by the other crabs in the 
container. When the pair broke apart the male 
took up an aggressive stance, lying over the 
dorsal surface of the female. 
The behaviour described above supports as 
far as possible Knudsen’s generalizations for 
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