122 BULLETIN OF THE BUREAU OF FISHERIES. 



An oligochsete worm, ChcBtogaster limruEi, is occasionally found in mussels. It is 

 possibly a parasite of snails from which it now and then migrates to mussels. We have 

 some reason to believe that it devours the other mussel parasites. The crystalline 

 Style, a long translucent gelatinous body which is formed by the mussel within its in- 

 testine, is often mistaken by clammers for a worm. 



Certain protozoa, Conchopthirus curtus and Conckopthirus anodonicE, somewhat 

 resembling in general appearance the slipper animalcule, Paramoecium, are occasionally 

 met in the mucus of mussels. Attached protozoa, like Vorticella, are also occasionally 

 found on the edge of the mantle. 



Occasionally larval Atax migrate into the space between the mantle and shell 

 and are covered by nacre, where they may form minute white tracks, or in some cases 

 apparently small raised "blisters" or pimples (Clark and Gillette, 1911). One or 

 perhaps several species of distomid causes a brick-red or purplish discoloration of the 

 nacre, mostly in thin-shelled mussels (Anodonta and Strophitus) (Osbom, 1898; Kelly, 

 1899, p. 406; Wilson and Clark, 1912, p. 66). The marginal cyst distomid sometimes 

 causes a steel-blue stain of the nacre near the margin (Wilson and Clark, 1912, p. 63). 



ENEMIES. 



Mussels have numerous enemies, among which may be mentioned the mink, the 

 muskrat, the raccoon, water birds, turtles, fishes, hogs, and man. 



Of the depredation of many of these we know little. Water birds probably kill 

 but few mussels, and of fishes, catfish and the sheepshead, or fresh-water drum, are 

 the most noteworthy. These probably feed mainly on the thinner-shelled species. 

 Small mussels (Lampsilis parva) have been found in the intestines of the turtle, Mala- 

 clemmys lesueurii. 



Besides man the muskrat is the most notorious enemy of mussels, and the shell 

 piles left by them are often conspicuous objects along the shores of lakes and rivers. 

 Conchologists sometimes rely upon the muskrat's shell piles to furnish them choice 

 and rare shells. Evermann and Clark (1918, p. 284) found not a few examples of 

 Micromya fabaiis in muskrat shell piles on the banks of Lake Maxinkuckee, though 

 collecting in the lake during several seasons failed to reveal a single living specimen. 

 Clammers prospecting new rivers sometimes use the piles of shells left by the muskrat 

 as aids indicating where to dredge for shells. 



Direct observations of the work of muskrats in L,ake Maxinkuckee, Ind., were made 

 by Clark and reported in "The Unionidae of Lake Maxinkuckee" (Evermann and Clark, 

 1918, pp. 261, 262), as follows: 



The greatest enemy of the lake mussels is the muskrat, and its depredations are for the most part 

 confined to the mussels near shore. The muskrat does not usually begin its mussel diet until rather 

 late in autumn, when much of the succulent vegetation upon which it feeds has been cut down by 

 the frost. Some autumns, however, they begin much earlier than others; a scarcity of vegetation or 

 an abundance of old muskrats may have much to do with this. The rodent usually chooses for its 

 feeding grounds some object projecting out above the water, such as a pier or the top of a fallen tree. 

 Near or under such objects one occasionally finds large piles of shells. The muskrat apparently has 

 no especial preference for one species of mussel above another but naturally subsists most freely on 

 the most abundant species. These shell piles are excellent places to search for tlie rarer shells of the 

 lake. 



In the winter after the lake is frozen, great cracks in the ice extend out from shore in various 

 directions, and this enables the muskrat to extend his depredations some distance from shore in defi- 



