HAPALOCARCINUS, THE GALL-FORMING CRAB, WITH SOME 
NOTES ON THE RELATED GENUS CRYPTOCHIRUS. 
By F. A. Ports, M. A. 
HAPALOCARCINUS MARSUPIALIS Stimpson. 
INTRODUCTION.* 
Hapalocarcinus is a genus of Brachyrhynch crabs, the individuals 
of which are very small in size and profoundly modified, owing to 
the fact that they pass the greater part of their lives confined in small 
cavities in coral colonies. At an early age the female crab settles 
between two adjacent branches, usually terminal, and so influences 
their further growth that they broaden and, later, unite to form the 
so-called gall, a lenticular or spherical structure about the size of a 
hazel nut. Within this is the living chamber of the crab, which com- 
municates with the outside water by a series of apertures. The animal 
thus becomes sedentary, never leaving its gall and producing enor- 
mous broods of larve. 
Hapalocarcinus marsupialis was first described by Stimpson between 
1856 and 1859 from specimens ‘‘found clinging to the branches of living 
madrepores in the harbour of Hilo, Hawaii.”” It was thus thought at 
first to be a free-living animal, but Verrill, in 1867 (6), pointed out 
that certain ‘‘deformities on corals,’’ compared by Ehrenberg to the 
galls formed by the influence of insects on plants, are in fact caused 
by Stimpson’s Hapalocarcinus. He describes the phenomenon in the 
following passage: 
‘“‘ Another peculiar mode of parasitism I have observed in a singular crusta- 
cean (Hapalocarcinus marsupialis, Stimpson) from the Sandwich Islands. 
This creature lodges itself among the slender branches of a coral (Pocillopora 
cespitosa, Dana) and causes, probably by its incessant motions, the branches 
to grow up and often interlock above, leaving openings between them suitable 
for the uses of the parasite but usually too small to allow of egress. Most 
specimens of the corals of this species sustain one or more and often numerous 
examples of these curious enlarged bulbs among the branches.” 
In subsequent papers (7, 8) he makes further observations on the 
occurrence of ‘‘galls,’’ without adding much to the above description. 
Karl Semper became well acquainted with Hapalocarcinus (and the 
related form Cryptochirus) during his researches in the East Indies. 
In his well-known book on ‘‘The Natural Conditions of Existence as 
they Affect Animal Life’? (published in English, 1881) he illustrates 
*His duties as an officer in the English Army made it impossible for Mr. Potts to eontect 
the proof of this paper.—A. G. M. 
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