Observations on the gastric epithelium of ascidians with special reference to Styela clava

Summary Transmission electron microscopy shows the gastric epithelium of Styela clava to comprise at least three distinct cell types. Ciliated mucous cells which form the crest of each stomach ridge produce mucus by an unexpected route. Vacuolated cells lining the ridge sides appear to be absorptive in function. Gastric enzymes are produced by typical protein secreting cells scattered amongst the vacuolated cells. Undifferentiated cells are found in the crypts between ridges. The structure and function of the gastric epithelium in Styela is discussed with special reference to the wider concepts of ascidian gut organization.The author is grateful to Mrs. L. Rolph for technical help with scanning electron microscopy and Mr. J. Calvert and Mr. R. Jones for assistance with the transmission electron microscopy. Animals were collected through the kind offices of Mr. J. Sturges and other staff of the Admiralty Marine Trials Station, Portsmouth. This research was carried out during the tenure of SRC grant No. B/RG 82919 -The localization of polypeptide hormones in the pharynx and gut of Protochordates