SHORTER ARTICLES AND DISCUSSION 



SEX-CORRELATED COLORATION IN CHITON 

 TUBERCULATUM 1 



1. Among mollusks the occurrence of clear-cut differential 

 characters associated with sex is rare. Differences of size in the 

 sexes of dioecious species are known, though in some instances 

 the larger size of the female is a consequence of protandric her- 

 maphroditism ; there are also certain records of slight, and pos- 

 sibly inconstant, sex-differences in shell form; the hectocotylus 

 of dibranchiate cephalopods, however, is almost the only well- 

 defined instance of a " secondary sexual character" in mollusks 

 — and this is an accessory organ of copulation. Color differences 

 of this nature seem not to have been observed. Some importance 

 may tli ere fore be attached to the description of a pronounced 

 color difference, correlated with sex, which has been found in 

 the commonest placophoran at Bermuda, Chiton tuberculatus 

 Linne, particularly since this differential coloration seems 

 capable of interesting interpretation in several directions of 

 theoretic importance. 



2. In adult chitons of this species there is noticeable what ap- 

 pears at first sight to be a considerable diversity in the degree 

 to which pigment, of a salmon-pink hue, is developed upon the 

 foot and other soft parts exposed in ventral view. Somewhat 

 less than half of the individuals have the foot, ctenidia, and 

 other soft parts of a pale buff color; in the remainder, the foot, 

 head, ctenidia and mantle are to various degrees tinged with 

 salmon-pink or orange-red pigment, the color being in some 

 cases startlingly vivid. This difference is most pronounced dur- 

 ing late spring, but persists to some extent throughout the year. 

 The pigmentation is not correlated in any way with size; indi- 

 viduals of any length from 3.4 to 9.2 cm. may be either pale buff 

 or salmon-pink on the ventral surface ; nor does the intensity of 

 reddish pigmentation, when present, depend upon size. In 

 dorsal view it is quite impossible to distinguish the two groups 

 of animals, unless the plates be artificially separated to an ex- 

 treme degree, and not even then with any certainty. 



The differential coloration proves to be correlated with sex, 

 i Contributions from the Bermuda Biological Station for Besearch, No. 109. 

 84 



