MARSUPIAL ANATOMY OF THE DEMIBRANCH OF MARGARITIFERA MARGARITIFERA (LIN.) IN NORTHEASTERN NORTH AMERICA (PELECYPODA: UNIONACEA)

On morphological, biological and behavioral characters the freshwatermussel family Margaritiferidae generally is accepted as themost primitive of the Unionacea. Microscopic examination ofthe marsupial demibranch further supports this assumption, inthat the interlamellar junctions lack elastic properties necessaryfor lateral hyperextension of the gravid demibranch. A temporarymodification of marsupial anatomy in the form of a fibrous elastinaccessory material is produced during the final phase of glochidialincubation. Its appearance coincides with the enlargement ofepithelial cells that line the marsupium and interlamellar junctions.The material, which is situated between the glochidial massand the inner lamellar surfaces, may provide increased aerationand support for the resting glochidia. (Received 18 February 1978;