SOME STRUCTURAL VARIATIONS IN CHROMODORIS ZEBRA. 



W. J. CROZIER. 



Contributions from the Bermuda Biological Station for Eesearch, No. 64. 



Abnormalities of a minor character are by no means uncom- 

 mon in nudibranchs, and, while these features are usually not 

 of any great morphological significance, some of them seem 

 sufficiently curious to warrant description. I have noted sev- 

 eral such deviations from the typical structure while examining 

 a large number of specimens of Chromodoris zebra Heilprin. 



Small wood (1910) has described some of the variations in 

 the coloration of this animal, and has also referred to the vari- 

 ability shown by the branchire, particularly in the manner in 

 which one or several of these organs terminate by division of 

 their free ends into several parts. I have elsewhere (Crozier, 

 1917) made note of the variation in the number of the glandu- 

 lar papillae which occur upon the ventral surface of the poster- 

 ior border of the mantle. 



Variation in the branchiae is, in fact, somewhat more frequent 

 and more extensive than Smallwood observed. Not unusually, 

 bra.ncb.ise are to be seen which not only divide to a greater or 

 less extent at their tips, but also show a branching at some 

 distance from the tip (Fig. 1). In many instances the presence 

 of an accessory branchia arising in this way is unaccompanied 

 by duplication of the pointed tips. 



The high sheath which surrounds the branchial rosette is 

 normally quite smooth. In only one of the many hundreds of 

 Chromodoris which I have handled was there noted any other 

 condition. In this single specimen, however, there were three 

 distinct ridges running from the dorsal surface to the external 

 margin of the branchial collar ; two of these ridges were ex- 

 tended in an anterior direction, their edges being sharp and 



