. Animal biology. Zoology; Biology. FRESH-WATER MUSSEL 215 marsupium and to be carried out of the dorsal siphon by the currents of water flowing through the body. Since the unios usually live in running water, their glochidia are swept along by the current until they are carried into the mouths of fish with the water which the latter use in respiration. As they pass the gills of the fish they attach themselves to the gill fila- ments, clinging by the valves of the shell and also, perhaps, attached by the larval thread, which penetrates the tissues. The closure of the valves seems to be due to
. Animal biology. Zoology; Biology. FRESH-WATER MUSSEL 215 marsupium and to be carried out of the dorsal siphon by the currents of water flowing through the body. Since the unios usually live in running water, their glochidia are swept along by the current until they are carried into the mouths of fish with the water which the latter use in respiration. As they pass the gills of the fish they attach themselves to the gill fila- ments, clinging by the valves of the shell and also, perhaps, attached by the larval thread, which penetrates the tissues. The closure of the valves seems to be due to chemical stimulation by salts escaping from the tissues of the fish. On the gills of the fish the larvae live a parasitic existence. Fig. 122.—Shell of a unio, Quadrula undulata (Barnes). From the Grand River, Michigan. For comparison wnth the anodonta type, Figs. 116 and 117. This is one of the species most sought for button making. X %. until development is completed and they are ready to metamorphose into small adults. After this has occurred they escape from the fish, fall to the bottom, and begin an independent Hfe. 256. Other Fresh-water Mussels.—A large number of species of mussels, belonging to several genera, may usually be found in any portion of this country. They differ markedly in size and shape and in the details of structure. They may be all grouped under two types—the stream type, known in a general way as unios, and the quiet-water type, known as anodontas. The former (Fig. 122), usually found in running water, are generally stationary, have thick shells with prominent hinge teeth, and the glochidia develop mostly in the gills of fishes, though they may also be attached to external surfaces. The anodonta type (Figs. 116 and 117), on the other hand, includes forms that live in still water, moving. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these i
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