THE ULTRASTRUCTURE AND FUNCTION OF THE OESOPHAGUS OF PATELLA VULGATA LINNAEUS

The oesophagus of Patella vulgata Linnaeus is divisible intotwo histologically and functionally distinct regions, a centralfood channel and a series of lateral pouches forming the oesophagealglands: both are lined by a glandular ciliated columnar epithelium.Subepithelial mucous cells are restricted to the epitheliumlining the food channel and posterior section of oesophagus,whilst amylase-secreting cells occur only in the oesophagealglands. The activity of the ciliated cells lining the food channelmixes ingested food with saliva and mucus to form a food stringthat is carried towards the stomach. Amylase-secreting cellsproduce an extracellular amylase in the form of proteinaceoussecretory granules, which are released by apocrine secretionwithin cytoplasmic blebs. Release is correlated with periodsof immersion when feeding is possible. The free blebs are carriedout of the pouches and into the food channel where the amylaseinitiates carbohydrate digestion. The oesophageal epitheliumabsorbs tritiated D-glucose by a Na⁺-dependent mechanism inhibitedby 2,4-DNP and phloridzin and the amylase-secreting cells pinocytoseferritin. It is suggested that the oesophagus absorbs smallsolute molecules derived from ruptured algal cells and theirpartially digested polysaccharide storage products. There alsoappears to be pinocytosis of dissolved organic matter. ^*Current address: The R L. Weston Institute for NeurologicalStudiet, University College & Middlesex Medcal School, MortimerSt., London Wl. (Received 8 March 1988; accepted 29 April 1988)