ULTRASTRUCTURAL EVIDENCE THAT GASTROPODS SWALLOW SHELL RASPED DURING HOLE BORING

¹ College of Marine Studies, University of Delaware, Lewes, Delaware 19958

1. Observations are reported on the ultrastructure of shell material rasped by Urosalpinx cinerea follyensis Baker from boreholes in the valves of Mytilus edulis Linné and transported normally to the stomach through the buccal cavity and esophagus. Duration of the period of chemical activity by the accessory boring organ and rasping by the radula were determined with a valve model. Pellets of shell raspings were removed from the stomach and, after fracturing to reveal the interior, and coating with metal, were studied with the scanning electron microscope. Shell raspings were compared with prisms and lamellae in fracture surfaces of normal shell of M. edulis and shell etched with ethylenediamine and sodium hypochlorite to reveal the form of shell units clearly.

2. The study provided ultrastructural evidence for the first time that Urosalpinx cinerea swallows shell rasped from the borehole during penetration of prey. Both prisms and lamellae were identified in the pellets removed from the stomach. Noticeable dissolution of the organic matrix, and to some extent also of the mineral portion, of prisms was evident, features which facilitate removal of shell by the snail during rasping.

3. If the long axis of prisms occurs parallel to the surface of the borehole, the radula tends to rasp out long fragments of shell; if prisms are placed at right angles to the surface, the radula breaks prisms into small pieces.

4. The envelope of mucoid material which coats pellets undoubtedly reduces, or prevents, laceration of the epithelium of the alimentary canal as shell fragments pass down the tract.

5. A gross approximation of the percentage of shell in the borehole which is rasped and swallowed during the process of hole boring is 14%.