THE SEASONAL INFESTATION OF NASSA OBSOLETA 

 (SAY) WITH LARVAL TREMATODES. 



HARRY M. MILLER, JR., AND FLORA E. NORTHUP, 1 

 WASHINGTON UNIVERSITY, SAINT Louis. 



The purpose of this investigation has been to make a twelve 

 months' survey of large numbers of a single species of marine 

 mollusk, to determine what different larval trematodes para- 

 sitize it, and especially to determine and to try to interpret the 

 seasonal fluctuations in the degree and character of the infes- 

 tation. The study was begun at the Marine Biological Labo- 

 ratory, Woods Hole, Massachusetts, in August, 1924, when 

 several common species of gastropod were collected in Quam- 

 quisset Harbor. Examination at that time showed Nassa 

 obsoleta, the common mud snail, to be the most heavily para- 

 sitized, and therefore this species was chosen as the one for study 

 throughout the year. The biology and ecology of this snail 

 have been studied by a number of investigators (see especially 

 Dimon, 1905; Sumner, Osburn, and Cole, 1913; Allee, 19230, 

 19236). The work was continued at the Zoological Laboratory 

 of Washington University with snails shipped periodically from 

 Woods Hole, and the twelve months' survey was completed at 

 Woods Hole during the summer of 1925. All collections were 

 made from a fifty yard area in the part of Quamquisset Harbor 

 known as Gansett; a total of 8,875 individuals of Nassa obsoleta 

 were examined. In addition to the data on the seasonal infes- 

 tation brief descriptions of the larval trematodes are also in- 

 cluded. 



HISTORICAL. 



Relatively little work has been done on marine larval trema- 

 todes, and that chiefly by European investigators. Among these 

 Pelseneer (1906), Sinitsin (1911), and Lebour (1905-1912) have 



1 The routine examination of snails and collection of data for descriptions of 

 the trematodes are almost wholly tin- \\ork of the junior author, as are all drawings 

 except numbers 2, 9, n and 17. 



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