A NOTE ON THE METAMORPHOSIS OF THE 

 MUSSEL LAMPSILIS L^VISSIMUS. 1 



ROBERT E. COKER AND THADDEUS SURBER. 



While making a collection of the glochidia of various species 

 of mussels used in this laboratory certain observations have been 

 made which prompt the publication of a preliminary note on the 

 peculiar type of glochidium seen in Lamps His Icevissimus and 

 other species, and the metamorphosis during the period of 

 parasitism. 



i. TYPE OF GLOCHIDIUM AND POSSIBLE SIGNIFICANCE. 



The glochidium of Lampsilis alatus has been observed by 

 Lefevre and Curtis, 2 who describe it as an " axe-head " glochidium. 

 "This possesses hooks which are not homologous with those of 

 the anodonta type and is to be regarded as more nearly related 

 to the hookless forms, an interpretation which is borne out by 

 the fact that the 'axe-head' can be readily imagined as a 

 modification of the glochidial outline seen in some species of 

 Lampsilis, which, like subrostratus, show an approach to a 

 rectangular outline." 



This glochidium (Figs. 3 and 30) is certainly of a very special- 

 ized form. In our laboratory we have observed an almost 

 exactly similar glochidium in L. capax (Figs. 4 and 4a), while in 

 L. Icevissimus (Figs, i and ia) the same shape is 'observed but 

 the hooks are wanting. It is remarkable that a larva of so 

 specialized a form should be found in two species such as alatus 

 and capax, the adult forms of which are so extremely opposed 

 in general shape; alatus is one of the most compressed forms in 

 the genus, while capax is the most inflated (Figs. 4^ and 4c). 



L. Icevissimus (Figs, ib and ic) and L. gracilis are forms sug- 

 gestive of alatus in the compressed character of the shell. They 

 are somewhat more compressed than alatus and are much thinner 



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

 Read by title before the American Society of Zoologists, December, 1910. 



2 " Reproduction and Parasitism in the Unionidae," Jour. Exp. Zoo/., Vol. IX.. 

 No. i, p. 94- 



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