Aquatic Invertebrates of Montana
The phylum Mollusca in a ancient group that is second in size only to the arthropods. There are over 50,000 living species and about as many fossil species known. Mollusks are unsegmented, coelomate protostomes with a ventral muscular foot, a shell-secreting mantle, and a radula as the feeding organ. They have a trochophore larval stage similar to the annelids and a later veliger larval stage. The circulatory system is open and excretion is by metanephridia. There are about 8 classes; Caudofoveata, Aplacophora, Monoplacophora, Polyplacophora, Gastropoda, Bivalvia, Scaphopoda, and Cephalopoda. Only Gastropoda and Bivalvia occur in freshwater in our area.
Updated on 16 DEC 1995 D.L. Gustafson
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