Mucocyte distribution and relationship to particle transport on the pseudolamellibranch gill of Crassostrea virginica (Bivalvia: Ostreidae)

To investigate particle transport mechanisms on the bivalve pseudolamellibranch gill, the mucocyte secretion types and distribution were determined for this organ in the eastern oyster Crassostrea virginica, and related to previous endoscopic data. Three adult oysters were collected from Shediac Bay (New Brunswick, Canada) in July 1994, immediately fixed, then dissected and processed for histology and whole mount mucocyte mapping using a modification of the periodic acid-Schiff-alcian blue protocol. One type of mucocyte contained acid-secretion mucopolysaccharides (AMPS), while the other type contained neutral mucopolysaccharides (NMPS). A clear gradient in mucocyte density was observed from the plical crest to the trough; for all but the anteriormost 15 plicae the proportions of each mucocyte type remained constant; the 15 anteriormost plicae presented an increased proportion of AMPS. These proportions would produce a relatively viscous acid-dominant mucus after mixing on the ciliated gill surface. The principal filament troughs contained relatively few mucocytes, aligned on the median ridge. This arrangement could account for the observed range oi particle velocities in these filaments. The results of the present study conform to a pattern of specialization of mucus types and functions on the diverse types of bivalve gill, depending on particle trajectory, transporting surface architecture, and dominant current flow.