215 



PROTECTIVE RESEMBLANCE IN BRITISH 

 MARINE MOLLUSCA. 



By J. A. H A RG REAVES. 



(Read before the Society, Nov. 9th, igio). 



The question of protection, and particularly colour protection in the 

 British marine moUusca, does not appear to have attracted much 

 attention. In the volume on Molluscs and Brachiopods in the Ca/n- 

 bridge Natural History several instances are given of nudibranchs 

 which are protective or warning in colouring or in habitat, or by 

 disagreeable taste; but among the shell-bearing mollusca only three 

 British examples are given, viz.. Chiton, Littoriiia obiusata on Fucks 

 vesiculosus and Helcioii fieiluciduui on Laminaria. 



While admitting that Littoritia obtusata may gain some advantage 

 from its resemblance to the air-bladders of the Fticus, it must be but 

 slight if pursued by animals of normal vision, as it is easily visible at 

 a considerable distance; whilst it appears to me- that Helcion pelluci- 

 dum is rendered more conspicuous by the blue rays which are claimed 

 as protective. 



In this part of Yorkshire, however, we have a case of what I cannot 

 but regard as colour protection, which is undeniably serviceable, the 

 protection being so marked as to render the shell almost invisible 

 even at close quarters. I refer to Aancea virginea (Miiller) which on 

 our coast is common, but is most difficult to find unless its habitat is 

 known. 



Our rocks between tide-marks vary from an iron-stained sandstone 

 to a bluish-black shale, and odd specimens of Acmcea may be found 

 on rocks in pools drained by the tide but never left dry. If wanted in 

 numbers, however, another method of search must be adopted. 



AVe have at Scarborough a nullipore LithotJianuiion polymorphuni 

 Aresch'(kindly named for me by Professor Herdman, of Liverpool), 

 which clothes many rocks with a pink coating, with which the "pink- 

 rayed limpet" harmonises marvellously. Not only is this the case but 

 the mollusc is much more abundant on the nullipore than elsewhere; 

 so much so that I could gather more specimens on an average square 

 yard of the nullipore than on a hundred square yards of uncoated 

 rock. Even for an experienced collector it is necessary to examine 

 the nullipore minutely over and over again to obtain all the specimens 

 exposed, so completely does the background agree with the shell 

 coloiir. 



