CHAPTER XXXVII 



FRESH-WATER MUSSEL 



A TYPE OF THE PHYLUM MOLLUSCA 



Fresh-water mussels are found in ponds, lakes, or streams. In ponds 

 or lakes, where the water is quiet, they lie nearly buried in the mud at the 

 bottom, moving about from time to time and leaving a furrow to mark 

 the path which they have followed. In running streams they are found 

 most abundantly where the water runs rapidly and where plenty of food 

 is brought to them. In such locations they are sedentary, remaining 

 wedged in between the stones and protected from the force of the current 



Umbo^ ^H/h^e ligament 



■Exhalenf 

 siphon 



Inhalenf 

 siphon 



L/ne o/ 

 growth 



Fig. 116. — Anodonta grandis Say. From a preserved specimen from Nebraska. 

 X M- A typical fresh-water mussel. The lines of growth are numerous but only the 

 most pronounced are annual lines. This specimen was probably in its sixth year. 



which would otherwise sweep them down into quiet pools where they 

 might be buried in the mud. Because of this danger of being buried by 

 the deposition of mud they are not often found in the broad, deep estuaries 

 of such a river as the Mississippi or in wide, shallow rivers which carry 

 large amounts of sand and detritus, such as the Missouri, the Platte, and 

 the Kansas. 



243. External Appearance. — A typical mussel is oval when viewed 

 from the side, the anterior end being rounded and the posterior pointed 

 (Fig. 116). The thickness is greatest at a point above and behind the 

 middle of the body and near the dorsal side; from this point it diminishes 

 in all directions but more gradually toward the ventral side, the margin 

 forming a sharp edge anteriorly, posteriorly, and ventrally. A cross 

 section has the outUne of a conventional heart (Fig. 118). The animal is 



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