MORPHOLOGICAL AND MOLECULAR CHANGES DURING METAMORPHOSIS IN UTTERBACKIA IMBECILLIS (BIVALVIA: UNIONIDAE).

This study examines morphological and biochemical changes that occur as glochidia larvae of the freshwater mussel Utterbackia imbecillis (Say, 1829) metamorphose into juveniles. Metamorphosis encompasses two distinct stages. The first occurs during the first 3-4 days, and involves degeneration of the single larval adductor muscle and formation of the characteristic mushroom body by the larval mantle cells. These morphological changes are accompanied by an increase in DNA, RNA, and protein synthesis. The second stage occurs during the final 4 days of the metamorphic period and involves formation of the major anatomical structures and organ systems of the juveniles. This stage also is accompanied by an increase in DNA, RNA, and protein synthesis. The de novo development of the juvenile adductor muscles is described, and sites of DNA, RNA, and protein synthesis are identified.