The Benthic and Pelagic Habitats of the Red Crab, Pleuroncodes planipes 
Carl M. Boyd 1 
In March 1895, several specimens of an un- 
described anomuran crab were washed ashore 
at Monterey, California. These, along with 
some similar animals found in oceanic waters 
(24°N, 130°W), were sent to William Stimp- 
son, who was describing the crustacean ma- 
terial collected by the North Pacific Exploring 
Expedition. Stimpson described both the Mon- 
terey and the high seas specimens as a new 
genus and a new species, Pleuroncodes planipes , 
assigned to the family Galatheidae (Stimpson, 
I860). The "red crab" or "pelagic crab" (Fig. 
1) is familiar to inhabitants of Baja California 
and occasionally is seen along southern Cali- 
fornia beaches, where large numbers of these 
animals are at times washed up and left 
stranded by receding tides. Their brilliant red 
coloration, together with their relatively large 
size, makes such occurrences of these animals 
a striking phenomenon. The present study was 
undertaken as an investigation into the pelagic 
distribution and possible benthic nature of the 
species; prior to this study P. planipes was 
believed to be only planktonic. 
Members of the family Galatheidae are typi- 
cally benthic when adult and are commonly 
known as "squat lobsters." Larvae of all the 
species are pelagic for at least a short time, 
and presumably the small postlarvae can alter- 
nate between the plankton and the benthos be- 
fore assuming an exclusively benthic life. Two 
antarctic species, Mtinida gregaria (Fabricius) 
1793 and M. subrugosa (White) 1847, may 
be either pelagic or benthic as adults, but are 
more commonly benthic (Matthews, 1932). 
The young of M. gregaria — the so-called 
Grimothea stage — are predominantly pelagic 
and have been reported on several occasions 
as so numerous that they color the sea bright 
red over large areas (Matthews, 1932; Bary, 
1953). P. planipes probably has evolved from 
stock that was benthic, for of the 230 described 
1 Institute of Oceanography, Dalhousie University, 
Halifax, Nova Scotia. Manuscript received July 21, 
1966. 
species in the family Galatheidae only the 
two species of Munida discussed above and 
P. planipes are ever planktonic as adults. 
In the new genus Stimpson also included a 
Chilean species described by Milne-Edwards 
(1837) as Galathea monodon, which hence 
became Pleuroncodes monodon) these are the 
only two species assigned to the genus at 
present. Initial descriptions of the two species 
are quite inadequate. Milne-Edwards’ descrip- 
tion of G. monodon morphologically fits most 
of the species of Munida, a large genus closely 
related to Pleuroncodes and containing about 
41 species; however, his figures of G. mono- 
don, published in 1851, are excellent. Stimp- 
son’s description of P. planipes (I860) is only 
slightly better; he did not present any figures 
of the new species, which apparently was first 
illustrated by Schmitt (1921). Schmitt’s de- 
scription of P. planipes is the most complete 
to date. P. monodon is described by Faxon 
(1895) and Haig (1955). The larval stages 
of P. planipes have been described in earlier 
papers (Boyd, I960; Boyd and Johnson, 1963). 
A fossil specimen probably belonging to 
Pleuroncodes was found by Carl L. Hubbs, of 
Scripps Institution of Oceanography (Miller, 
1951). This specimen was from a sea cliff of 
the Capistrano Formation (an Upper Miocene 
deposit), about 1 mile south of Capistrano 
Beach, Orange County, California. It is not 
known whether the fossil was P. planipes, al- 
though the specimen was found well within 
the present-day distributional range of the 
species. 
Specimens of P. planipes freshly taken by 
dipnet from the ocean surface immediately 
settle to the bottom of a shipboard aquarium 
and assume a benthic existence in sharp con- 
trast to their pelagic life of a few moments 
earlier. Crabs kept in laboratory aquaria for 
growth studies lived almost entirely as benthic 
animals. It was believed that the question of 
whether the crabs were benthic in nature could 
not be answered conclusively by observations 
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