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A description of the ultrastructure of the gills of freshwater bivalves, including a new structure, the frontal cirrus

Way, Carl M., Hornbach, Daniel J., Deneka, Tony, Whitehead, Russell A.
Canadian journal of zoology 1989 v.67 no.2 pp. 357-362
Corbicula fluminea, Musculium transversum, Polymesoda caroliniana, cilia, clams, gills, interspecific variation, physiology, ultrastructure
The archetypical gill structure of lamellibranch bivalves has been the focus of research concerning the feeding mechanisms of these clams. In recent years there has been debate over whether the lamellibranch gill acts as a sieve or whether the gill ciliature produces hydromechanical shear forces for the capture of particles during feeding. In corbiculacean bivalves, the gill shows considerable interspecific variability in the integrity of the ciliary tracts. A novel ciliary structure, the frontal cirrus that varies in organization, distribution, and abundance in the three species studied, has been found. In Musculium transversum the cirri are found only on the outermost margins of the inner demibranch and are composed of a tight bundle of cilia originating on the posterior side of the gill filament. The cirri in Corbicula fluminea appear as either a tight bundle or a loose aggregate of cilia, originating on the posterior side of the gill filament between the frontal cilia and the laterofrontal cirri; the frontal cirri cover the entire demibranch except in the area near the food groove. The frontal cirri in Polymesoda caroliniana are similar in structure and distribution to those found in C. fluminea. The frontal cirri are hypothesized to play an important role in the feeding physiology of these bivalves.