Date Awarded


Document Type


Degree Name

Master of Arts (M.A.)


Virginia Institute of Marine Science


The genus Bittium in the Western Atlantic was studied to determine the number and distribution of extant species. Shells of adults and juveniles collected from Brazil to Canada, including the type specimens of B. virginicum, were examined and compared on the basis of length, lengthwidth ratio and varix presence or absence. Although intergrades of B. alternatum and B. varium probably existed in the middle Chesapeake Bay, along the Atlantic shores of the Delmarva Peninsula and New Jersey, and in western Long Island Sound prior to 1940, B. alternatum is now found from Shark River, New Jersey, northward and B. varium from Chesapeake Bay, s outhvlard. There are presently no Bittium between Shark River, New Jersey and Cape Charles, Virginia excepting the B. var.i·um in Chesapeake Bay. Destruction of the eelgrass habitat in the 1930's is the probable cause of :.the absence of Bi ttium in the area of former intergradation. Larger size and lack of a varix distinguish adult B. e1lterna.tum from adults of the smaller, more slender .!}.. Juveniles are more difficult to separate since neither species possesses the varix as juveniles, but juvenile B. alternatum are usually wider than juvenile B. var.ium and attain greater lengths before formation of an apertural canal with maturity. B. virginicum·is considered a growth form of B. varium.



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