MAEINE CRUSTACEANS. 271 



Family Hapalocarcinidae. 



This interesting little family of symbiotic crabs, of which, in one case, only the females 

 are known, is, as Caiman has shown [TV. Linn. Soc. Zool. (2), viii. p. 43 (1900)], quite incertae 

 sedis, and is taken here for convenience alone, and not on account of any relationship to the 

 Xanthidae. It is discussed at length in Caiman's paper. For some remarks on the import- 

 ance of these crabs as affording by their holes a foothold for destructive boring organisms 

 in the coral blocks, see a paper by Mr Stanley Gardiner in this part of the present 

 publication. 



Genus Hapalocarcinus Stimps., 1857. 



1. Hapalocarcimos marsupialis Stimps., 1857. Caiman, loc. cit. 



Galls containing specimens of this crab were found on Pocillopora in the lagoon at 

 Minikoi and on the reef at Hulule, Male Atoll. 



Genus Gryptoclm-us Heller, 1861. 



2. Gryptochirus coralliodytes Heller, 1861. 



Cryptochirus coralliodytes, Heller, S. B. Ak. Wins. Wien, XLiii. i. p. 366, pi. II. figs. 33—39 

 (1861); Semper, Anirnal Life, London, 1881, pp. 217, 221—223; Caiman, loc. cit. p. 47. 



Mr Stanley Gardiner has kindly given me the following note on this species : " A block 

 of Leptoria tenuis which had a large number of round holes on the surface, up to 4 mm. 

 across, was broken up. The holes, when traced in, were nearly all found to be occupied 

 by a symbiotic crab [Cryptochirus]. In two holes, however, were crabs of the ordinary form 

 [Pseudozius, see above, p. 241]. The holes varied in depth from 1 — 30 mm., the coral itself 

 being in the latter position 48 mm. thick. Normally the animal would appear to live close 

 to the surface — some slightly projected, with the carapace as a kind of shield closing the 

 hole. When the block becomes more or less dry, they retreat into the bottom of the holes. 

 I found some deserted holes, perhaps due to an accident in breaking the coral, but the crabs 

 certainly could not wander, on account of the small size of the entrances of the holes. It 

 is obvious that the crab must have taken up its abode on the coral, which afterwards 

 enclosed it. [This refers to the inner hole, not to the funnel round it.] These commensals 

 are extremely common in Leptoria from the lagoon at Minikoi, but are never found in 

 specimens from the outer reef They are rare on other corals, occasionally occurring in 

 massive astraeids from the lagoon at Minikoi, but not apparently in branching corals, fungoids, 

 or perforate corals." 



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