NOTES ON BRANCHIOBDELLA. 



\V. M. SMALLWi )OD. 



So little is known concerning the American members of 

 P>rancliiobdclla that the following notes may be of interest. Dur- 

 ing the summer of 1905 a number of crayfish were taken by 

 dredging from Lake Clear, Harrietstovvn, Franklin County, N. Y., 

 in about eighteen feet of water. On all of the claws the cara- 

 pace, rostrum, and even on the abdomen there were large num- 

 bers of Branchiobdella instabilia Moore which Professor Moore 

 has kindly identified for me. I found associated with them a 

 few Branchiobdella pulcherrima and a half dozen Bdellodrilus 

 illuininatus. 



All of these are usually designated as external parasites but I 

 can see no reason for using this term. The word symbiosis or 

 commensalism more correctly describes the relation that exists 

 between the crayfish and Branchiobdella ; but these two terms 

 are used with such inconsistency to-day that we can find no 

 accepted definition of either. It is not easy to conceive how 

 Branchiobdella is of benefit to the crab. Their whitish appear 

 ance and constant movements make the crab more conspicuous 

 yet from their location and the fact that they are attached by the 

 posterior end suggest the probability that they do not receive 

 anything as food from the crab's body. 



The food of these forms throws some light on their habits. 

 A study of the digestive tube in both macerated and mounted 

 sections revealed the presence of large numbers of unicellular 

 algre and diatoms. The digestive tube was full and seemed to 

 contain nothing but small plants which would suggest that the 

 crayfish merely served to carry the worms around enabling them 

 the better to secure food so that it seems to me that the term 

 symbiosis used in its original and etymological sense gives a 

 better idea of these relations than does external parasite. 



All of these symbionts are continually in motion, stretching the 

 body out in every direction as if constantly feeling for something. 



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