68 



MUSSEL FAUNA OF MAUMEE EIVEK. 



duplicatum' and their contained cercarise live for a considerable time 

 in the water when removed from the host. Migration would there- 

 fore be possible. 



It has so happened that the Anodontas in which we fomid sporo- 

 cysts were all taken in early and middle summer, in July or August; 

 we found free distomids, however, as early as Avork in the field began, 

 in June, It would require the study of infected regions throughout 

 the year to ascertain whether the various phases in the life cycle of 

 this distomid bear any relation to the seasons. Von Baer found his 

 Anodontas affected by the sporocysts of D. duplicatiim in late autumn. 



5. The distomid of Kelly, — In several of the thicker-shelled species 

 of mussels, such as Lampsilis ventricosus, L. ligamentinus, Ohovaria 

 circulus^ and especially in Quadrula tuherculata and Unio gihhosiis^ 

 one frequently encounters pink distomids bearing a close similarity 

 to the distomid of Osborn mentioned above. Kelley,^ who first de- 

 scribed and discussed these distomids, was of the opinion that they 

 are identical with those described by Osborn as affecting Anodonfa 

 and Sti'ophitus and producing a discoloration of the nacre. 



Indications pointing to the identity of these two distomids are, 

 first, the fact that dorsal baroques are formed in Anodonta by the 

 distomid of Osborn, and second, that the distomid of Kelly, in addi- 

 tion to forming baroques in Ohovaria circulus^ frequently causes the 

 nacre to become rough and assume a yellowish color, approximating 

 the salmon color of affected Anodontas, 



In their typical form as they appear in the thick-shelled species of 

 mussels, these distomids exhibit several minor points of difference 

 from the distomid of Osborn. Practically they present so different 

 a set of manifestations that in our field notes it was found necessary 

 to separate them. 



After considerable study and comparison we are inclined to think 

 them the same, but in this discussion, since the point of view is 

 ecological rather than taxonomic, it will conduce to clearness to refer 

 to this manifestation of the species under a different name. Simi- 

 larly, it is convenient and customary to speak of the cercaria of a 

 distomid, the nauplius of a crustacean or the leptocephalus of an eel. 

 The distomid of Kelly is usually found in much fewer numbers than 

 that of Osborn, a fact which suggests that it may be erratic or 

 a stray migrant, and so far we have not found it associated with 

 sporocysts or cercarias except in the single instance of Quadrula 

 tuherculata referred to above. It is usually confined to the outer 

 surface of the mantle near the cardinal or lateral teeth of the mussels 

 affected, and it is frequently associated, as Kelly has pointed out, 

 with irregular dorsal baroques or pearls. It does not produce a 

 salmon-colored stain in the nacre of the mussel affected, and usually 



« Bulletin Illinois State Laboratory Natural History, vol. v, art. 8. 



J 



