The morphology, ultrastructure and function of the feeding apparatus ofSayella fusca (C.B. Adams, 1839) (Gastropoda : Pyramidellidae)

摘要

Scanning and transmission electron microscopy in conjunction with histology 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, including the buccal pump and proboscis anatomy, depart from the characteristic pyramidellid plan. Some differences such as the position of the introvert/proboscis aperture and the common oral and stylet canal are shared with the genera Turbonilla, Eulimella, and Pyramidella. Three characteristics of the feeding apparatus are unique to S. fusca: (1) the buccal pump is not divided into two pouches but exists as a single muscular bulb; (2) the entire lumen of the buccal pump, not simply a portion of it, possesses a cuticular lining; and (3) the salivary ducts never enter the muscular walls of the buccal pump. Histological studies of the salivary gland indicate that three types of secretory cells are intermittently distributed throughout the entire gland rather than characterizing distinct regions as described for other members of the family Pyramidellidae. In contrast to previous findings, the gland cells of S. fusca exhibit a merocrine secretion. The taxonomic value of the buccal pump and proboscis morphology are discussed.