PRELIMINARY NOTE ON THE ECOLOGY OF THE 

 EARLY JUVENILE LIFE OF THE UNIONID.E. 1 



F. B. ISELY. 



During the past four years the writer has given considerable 

 time to the field study of the Unionidae. A number of puzzling 

 questions have arisen as to the relative importance of the various 

 ecological factors that contribute to the environmental complex 

 of these animals. Among the most important of these factors, 

 we may mention bottom conditions, water content, stream vol- 

 ume, stream fluctuations, relation to fish and natural enemies. 



In connection with this work, much difficulty was experienced 

 in finding young mussels for study and experimentation. I have 

 collected many specimens from the size of a nickel to a quarter,, 

 but mussels under the size of a dime have been rare. A number 

 of experienced field workers have spoken to me of a similar 

 difficulty in finding juvenile specimens. 



In order to avoid any misunderstanding, I may state that by 

 "early juvenile life" I mean the period following the time when 

 the mussel completes the parasitic stage and leaves the fish to 

 lead an independent life, until it is about the size of a dime or 

 about fifteen millimeters in length. This would cover, in most 

 species, approximately the first year of independent existence. 

 Other periods may be designated as later juvenile and adult life. 



The glochidium stage has received considerable study. Our 

 knowledge of the parasitic period has been recently cleared up 

 and extended by the careful investigations of LeFevre and Curtis. 2 

 The later juvenile and adult life has received the attention of 

 hundreds of students. The scattering and meager references 

 in the literature, to the early juvenile stages, give us little infor- 

 mation on this important period in the life history of the mussel. 



During the past summer, while working on the Red River Mussel 



1 Published by permission of the U. S. Commissioner of Fish and Fisheries. 



2 "Reproduction and Parasitism in the Unionidse," George LeFevre and Winter- 

 ton C. Curtis, Journal of Experimental Zoology, Vol. IX., No. i, September, 1910, 

 pp. 79-115. 



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