CASES OF COMMENSALISM 



8r 



Dr. Norman suggests that the extreme flatness of the sliell of the 

 Lefton is of great advantage in enabling it not to get in the way 

 of the Gehia as he scuttles up and down his burrow. Another 

 species of Leftoii 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 Gchia? 



A very singular case of commensal ism has l_)een 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 plectorlnjnclius 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 Ephippodonta, a Kdlia and 



,-'^^^5K^-"«^^r^4 if SS^ 



Flf!. 32. — Epkippodonta Mac- 

 (louijalli Tate, S. Australia. 

 A, burrow of jirawn, the x 

 indicating the position of the 

 mollusc ; sp, sponge. B, 

 Ventral view of Ephippo- 

 donta ; by, byssus ; /, foot ; 

 m, mantle ; mm, fused mantle 

 borders. C, View of interior 

 of shells ; /i, hinge ; m'm' , 

 adductor muscles. (A x i ;, 

 B and C x 2. ) 





A 



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 whicli I 

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

 adhering very closely, are found the Ephippodonta. They (|uickly 

 form a pit -like depression liy means of their foot, and appear 

 almost covered by the mud." During the winter months (March- 



VOL. Ill 



SHmi)son, quoted by Jcffroys, Brif. Conch, ii. 194. 

 Slim[ison, Juunt. Bust. Soc. X. II. vi. 1S57, p. 48. 



