COMMENSAL ASSOCIATION. 



347 



consists in the presence of the crustacean within the suhumbrellar 

 space of the medusa, clinging- to the manubrium. Most of the 

 crabs were observed with the head directed downward, but a few 

 were situated with the head upward. In no case was more than 

 one crab found in a single medusa. They resisted detachment, 

 holding on tightly by means of the sharp and strongly curved ends 

 of their legs, and would occasionally attempt to escape by scram- 

 bling around the manubrium, just as a squirrel does around a tree 

 trunk. In such cases, however, their agility was not marked. 



At Georgetown and at Murrell's Inlet, S. C., in the north-central 

 region of the coastline, no examples of commensalism were ob- 

 served. One Lib'mia dubia was taken on the rocks of the jetties 

 at Georgetown, but no living medusae were seen at either station. 

 At Bluffton and at Sullivan's Island, in the south-central portion, 

 the following records were obtained : Bluffton, three medusae 

 seined from relatively deep water, each containing a crab ; no 

 other examples of either species were seen. Between Sullivan's 

 Island and the Isle of Palms, near Charleston, seventeen Stomo- 

 lophus were taken by net and by hand from shallow water, and 

 of these sixteen concealed a Libinia. In the remaining case, a 

 crab was found on the bottom in the immediate vicinity of the 

 jellyfish and the collector believed the crab to have just dropped 

 from his conveyor, probably due to the commotion in the water 

 which the numerous members of the party were causing. No 

 other examples of either species were encountered, so this suppo- 

 sition is strongly probable. The commensal crabs varied in size 

 but were all fully adult. At all four stations great numbers of 

 stranded medusae, mostly Stomolophus were seen along all beaches. 



Thus it is seen that ( i ) along the South Carolina coastline both 

 Stomolophus and Libinia are not uncommon and are frequently 

 abundant ; more so in the southern half, and especially true of the 

 medusa as attested by the many cast-up specimens. (2) With a 

 single exception, all examples of Libinia dnbia captured were 

 taken from the subumbrella of the medusa. (3) Again with a 

 single exception, and that one a doubtful case, all examples of" 

 Stomolophns niclcagris were found to harbor a crab. (4) All of 

 the observations were made in the month of May and involved 

 living adult stages of the commensals. 

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