THE HABITS AND REACTIONS OF A COMATULID, 

 TROPIOMETRA CARINATA. 



BY HUBERT LYMAN CLARK. 



INTRODUCTION. 



One of the most interesting echinoderms taken during the recent 

 visit of the Carnegie Institution's party to Tobago (March and April 

 1916) was the comatulid Tropiometra carinata (Lamarck). This crin- 

 oid was common in Buccoo Bay, and while Dr. Mortensen successfully 

 undertook the study of its development, I made such observations on 

 its habits and reactions as time and circumstances permitted. The 

 habitat of most of the individuals noted was so completely different 

 from any in which we had previously seen comatulids that we naturally 

 inferred the reactions would differ markedly from those of the species 

 studied in Torres Strait. 1 I therefore performed a few simple experi- 

 ments, the results of which are here recorded, together with such 

 observations as were made on the animal in its natural environment. 



SYSTEMATIC POSITION. 



Comparison of the comatulids taken at Tobago with a considerable 

 series of specimens from several stations on the Brazilian coast, south 

 of the Amazon, shows that they are unquestionably identical. For 

 this Brazilian species, Mr. A. H. Clark has revived an old name of 

 Gay's, picta, regarding it as "a perfectly good species," "most obvi- 

 ously differing from carinata in the greater length of the outer cirrus 

 segments" (Proc. U. S. Nat. Mils. 1911, vol. 40, pp. 35, 36). On com- 

 paring the Brazilian and Tobagoan material with specimens from 

 Mauritius and Zanzibar, I was utterly unable to detect any differences, 

 either in the cirri or in any other characters. On writing to Mr. Clark 

 of my difficulties, he very kindly replied that while the species of 

 Tropiometra are very difficult to distinguish, he finds "no difficulty in 

 distinguishing" the group in which he places picta from that in which 

 he places carinata, "by the difference in length of the outer cirrus seg- 

 ments." On receipt of his letter, I went over the cirri again, but I 

 found myself absolutely unable to detect the difference named. I 

 have therefore very reluctantly reached the conclusion that I can not 

 recognize picta as a valid species, but must designate my Tobagoan 

 comatulids by their old Lamarckian name. 



'Comatulids of Torres Strait, H. L. Clark, Carnegie Inst. Wash. Pub. No. 212, pp. 95-125, 

 1915. 



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