

STUDY ON THE HABITS OF THE CRAB DROMIA 



VULGARIS M.E. 



W. S. DEMBOWSKA, 

 M. NENCKI INSTITUTE FOR EXPERIMENTAL BIOLOGY, WARSAW. 



The crab Dromia vulgaris usually carries on its back a sponge 

 which it holds with the especially modified 4th and 5th pairs of 

 ambulatory legs. The sponges, found on crabs at Villefranche, 

 belonged to very different species. Only in the minority of cases 

 did the sponge belong to the species Suberites domtmcula, although 

 the symbiosis of Dromia and Suberites has become nearly a 

 classical instance. The sponges may belong to both the Calcarea 

 and Incalcarea groups and very often Dromia covers its back 

 with colonies of Ascidians, Algae, and even with pieces of paper 

 or rags of any possible color. The fact of the non-specificity 

 of this symbiosis was known to Polimanti and I believe that in 

 reality there is no true symbiosis at all, as the sponge seems to be 

 just as accidental a material as paper or rags. There is no doubt 

 that all the activity is on the side of the crab. 



The sponge ordinarily is astonishingly adapted to the size of 

 the crab and to the shape of its back, especially in young indi- 

 viduals. It seems to be an exact copy of the back's surface. The 

 cause of such a conformity is not exactly known. Renier uttered 

 the hypothesis that the larva of Suberites becomes fixed on the 

 back of a young Dromia and then both organisms grow together 

 which accounts for the conformity of shape. However, the 

 thing seems to be utterly improbable as there is no specificity in 

 the "symbiosis." The pieces of paper may be just as well 

 adapted to the size and to the shape of the crab as the sponge and 

 thus even if the theory of Renier proved to be true, it cannot 

 account for all the facts. Moreover the sponge is never fastened 

 to the back, but it is simply held by the crab. 



According to Vosmaer Dromia may tear off Suberites which are 

 fastened to the convex shells of molluscs, obtaining in this way a 

 concave surface that it puts then on its back. According to 

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