602 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



LOCOMOTION. 



Dr. H. L. Clark made extensive observations on the power of locomotion 

 shown by a number of comatulids which he studied at Mae'r Island, Torres Strait, 

 and from his account the following is taken almost verbatim : 



He says that to speak of the methods of locomotion in crinoids, or even in 

 comatulids, is like speaking of locomotion among birds, in that there is as much 

 difference between different kinds of comatulids as between different kinds of 

 birds, and as birds may either fly or run preponderatingly, so comatulids may 

 either commonly swim or creep. 



So far as the species studied at Mae'r are concerned, the Comasteridse are 

 creepers, while the other families represented there are swimmers. It was a sur- 

 prise and disappointment to discover that none of the common comatulids would 

 swim, even in the deep water by the live car, so that it was not possible to make 

 the observations and experiments with reference to the swimming of comatulids 

 which he had planned. When any of the species of the Comasteridse were placed 

 in the water beside the live car, they invariably sank to the bottom (about 20 

 feet). In the case of Comatella maculata it was noted that, as a rule, the indi- 

 vidual would close the arms orally and vertically over the disk, so that it sank 

 almost like a stone. As soon as it touched bottom the arms were opened out and 

 the animal began to creep. In the other species, however, the arms were not 

 closed up, and so the comatulids floated downward to the bottom much more 

 gradually. With one exception, all efforts to induce swimming movements of the 

 arms in a comasterid completely failed. 



In no case when the individual was on the bottom did mechanical stimulation 

 result in any attempt to swim, or in accelerated movements of any kind. Suspend- 

 ing specimens in the water by means of a slender thread gave no results; the arms 

 moved about slowly and with no coordinated effort, and with no resulting loco- 

 motion. Several individuals were provided with cork floats so attached as not 

 to interfere with their arm movements, but, with the one exception already referred 

 to, none of them made any effort to swim. The one exception was a small 

 Comatella maculata, which, after wearing the cork float in the live car for 24 

 hours, was dropped into deep water. It immediately began swimming, but spas- 

 modically and not in the beautifully coordinated manner of a Stephanometra. 

 Apparently these comasterids do not, under normal conditions, swim at all, but 

 could with sufficient effort be taught to do so. 



On the other hand, all of the species of the other families of comatulids 

 observed at Mae'r are good swimmers and do not creep about as the comasterids 

 do. They are usually found at rest on the lower side of rock fragments or on 

 a branch of coral with the arms more or less erect, but sometimes the arms are 

 opened out flat against the rock. They maintain their position by means of the 

 cirri, with which they often cling so tightly that it is difficult to dislodge them 

 without damage. Under no conditions did they seek to escape by swimming, but 

 when once dislodged swimming seemed to be their only means of locomotion. 

 Placed in a basin or a deep bucket of sea water, a very slight mechanical stimulus 



