THE EXISTENCE OF A SHORT REPRODUCTIVE 

 CYCLE IN ANODONTA IMBECILLIS. 



EDGAR ALLEN 

 I". S. BUREAU OF FISHERIES LABORATORY, FAIRPORT, IOWA. 



Fresh water mussels of North America have been classed by 

 Sterki (1895) as summer or winter breeders. He notes that in 

 winter breeders fertilization of ova occurs in the late summer, 

 embryonic development is completed and the fully developed 

 glochidia are carried through the winter in the maternal marsupia 

 and discharged in the following spring. In the summer breeders 

 fertilization occurs in the late spring or early summer and the 

 fully formed glochidia are discharged "as a rule by the end of 

 August." 



Lefevre and Curtis (1912) prefer to designate these two classes 

 as long and short term breeders. They include Anodonta in the 

 former group, and although A. imbecillis is not listed in the data 

 from which their conclusions are drawn, the statement is made 

 that the breeding season is a generic character, "all species of a 

 genus having essentially the same period of gravidity." 



In a table compiled by Coker, Shira, Clark, and Howard (1919) 

 gravid Anodonta imbecillis are listed for all months with the ex- 

 ception of April. 



Anodonta imbecillis, although not important commercially, is 

 of interest for two reasons; first, it is one of the two known species 

 which carry the young in the marsupia during metamorphosis 

 from glochidia to juvenile mussels, thus eliminating the parasitic 

 stage on fishes which other species undergo, and, second, it is 

 one of the few species which are hermaphroditic (Sterki, 1898). 



During the summer of 1922 the writer attempted to work out 

 a method of aparasitic mussel culture of commercially valuable 

 mussels. One line of attacking this problem which seemed to 

 offer promise of results was to simulate conditions pertaining in 

 metamorphosis during the intra-marsupial life of aparasitic 

 forms. Therefore a series of observations was begun on Anodonta 



imbecillis during the course of which successive examinations 



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