Ill 



CASES OF COMMENSALISM 



8i 



crustacean. Dr. Norman suggests that the extreme flatness of 

 the shell of the Lepton is of great advantage in enabling it not 

 to get in the way of the G-ehia as he scuttles up and down his 

 burrow. Another species of Lepton is found on the coast of 

 Florida in a precisely similar locality,^ while a third species, 

 occurring on the Oregon and California coasts, actually attaches 

 itself to the inner surface of the abdomen of a G-ehia?' 



A very singular case of commensalism has been recently dis- 

 covered with regard to a genus of Australian bivalve shells, 

 Ephippodonta. This genus is never found except in the burrow 

 of a species of prawn (^Axius plectorJiyncJius Str.). For some 

 reason at present unexplained, the burrow of this particular 

 prawn appears to be exceedingly popular as a habitat for certain 

 bivalves, for, besides two species of Ep]iipp)odonta, a Kellia and 



Fig. 32. — Ephippodonta Mac- 

 dougalli Tate, S. Australia. 

 A, Burro^\' of prawn, the X 

 indicating the position of 

 the mollusc ; sp, sponge. B, 

 Ventral view of Ephippo- 

 donta ; by, byssus ; /, foot ; 

 III, mantle ; mm, fused man- 

 tle borders. C, View of in- 

 terior of shells; h, hinge; 

 mm', adductor muscles. 

 (A X i ; B and C x 2.) 





three Mylitta are found there, and there alone. Sometimes the 

 prawn, when the rock is hard, builds a tunnel of mud upon it, 

 at other times it excavates the soft calciferous sandstone. " This 

 burrow is lined with a tenacious brown mud, composed of excre- 

 mentitious matter ; and, in addition to the mud lining, there is 

 always more or less present an orange-coloured sponge which I 

 have never found elsewhere. Upon the mud or sponge, and 

 adhering very closely, are found the Ephippodonta. They 

 quickly form a pit-like depression by means of their foot, and 

 appear almost covered by the mud." During the winter months 



1 Stimpson, quoted by Jeffrey's Brit. Conch, ii. 194. 



2 Stimpson, Joimi. Bost. Soc. X. H. vi. 1857, p. 48. 



VOL. Ill 



