THE MORPHOLOGY, ULTRASTRUCTURE AND FUNCTION OF THE FEEDING APPARATUS OF SAYELLA-FUSCA (ADAMS,C.B., 1839) (GASTROPODA, PYRAMIDELLIDAE)

Scanning and transmission electron microscopy in conjunction with hist ology and dissection were employed to investigate the foregut anatomy of Sayella fusca (C.B. Adams, 1839), a common New England pyramidellid snail. Certain aspects of the feeding apparatus of S. fusca, includin g the buccal pump and proboscis anatomy, depart from the characteristi c pyramidellid plan. Some differences such as the position of the intr overt/proboscis aperture and the common oral and stylet canal are shar ed with the genera Turbonilla, Eulimella, and Pyramidella. Three chara cteristics of the feeding apparatus are unique to S. fusca: (1) the bu ccal pump is not divided into two pouches but exists as a single muscu lar bulb; (2) the entire lumen of the buccal pump, not simply a portio n of it, possesses a cuticular lining; and (3) the salivary ducts neve r enter the muscular walls of the buccal pump. Histological studies of the salivary gland indicate that three types of secretory cells are i ntermittently distributed throughout the entire gland rather than char acterizing distinct regions as described for other members of the fami ly Pyramidellidae. In contrast to previous findings, the gland cells o f S. fusca exhibit a merocrine secretion. The taxonomic value of the b uccal pump and proboscis morphology are discussed.