On a new Sjiecies of Coral-infestintj Cruh. 211 



XX XT. — On a now Sjircies of ('oral-infesti)i;j Cruh taken by 

 the li.I.M.S. ' Invest i//fitor ' at the Andninan hiands. J5y 

 J. H. IIkndkksox, .M.H., F.L.S., Professor of Biology, 

 Madras Christian College. 



[Piute VIII.] 



The spceies described below is an interesting addition to 

 a small family of crabs which take up their abode ou 

 living corals, thereby causing abnormal growth in the latter, 

 ^\ith the production of a partially closed chamber or cavity 

 in which tiie crab is finally imprisoned. For its discovery 

 we are indebted to ^Nlajor A. R, Anderson, I.]\[.S., formerly 

 Surgeon-Naturalist of 11. M. Indian ^Marine Survey Steamer 

 * Investigator,' who as far back as 1899 forwarded specimens 

 to the present writer. 



The new species exhibits very striking sexual dimorphism ; 

 the dwarfed male, which is less than one fourth the size of 

 the female, reaching a total length of r25 mm., a length 

 which probably constitutes a record for diminutive size 

 among adult Decapod Crustacea. Another uni(jue peculiarity 

 of the male is his habit of attaching himself to the ventral 

 surface of the female, thus suggestin.g a comparison with the 

 condition existing in so many of the parasitic Crustacea 

 belonging to lower groups, though the more or less tempo- 

 rary nature of this attachment has not led to any degeneration 

 in the ca.-c of the male crab. In some at any rate of the 

 parasitic Crustacea, e. g. Bopyrus, the great reduction of the 

 male has perhaps arisen as a result of the female taking up 

 her abode in a confined space, and here, as in so many other 

 anim;d groups, similar habits have produced similar structural 

 peculiarities in genera not connected by near relationship. 



There can be little doubt tliat the coral-infesting crabs are 

 more common than the published records of their occurrence 

 would lead one to suppose, and both their small size and 

 peculiar habitat have led to their being overlooked by 

 collectors. They have hitherto only been recor.led from the 

 Hawaiian Is. [Sthnpson, VerriU), Red Sea (^Heller), Eeunion 

 {A. Milne- Eduards), Philippine Is., and an uudescribed form 

 Irom the West Indies [Semper), and Torres Straits [Caiman). 

 Ou the other hand, deformities on coral attributed to these 

 crabs, which were first aptly compared to plant-galls by 

 Eiirenberg*, have been described by numerous writers from 



* Elirenberg. in his work on the Corals of the Ked Sea, refers to a 

 small "Ptigiuus" which forms "galls" ou Seriatopora. The only 



