Observations on epithelial mucocytes in the sole of Patella species and Littorina littorea (Linnaeus, 1758)

The sole epithelia of populations of Patella vulgata Linnaeus, P. ulyssipon ensis Gmelin, and P. depressa Pennant, were examined by histology. There wa s no correlation between epithelial mucocyte density and animal size in any population. There was no significant difference in mucocyte density (mean +/- SE = 87.93 +/- 0.46 mm(-1)) in P. vulgata populations from different he ights on a moderately sheltered shore. Mucocyte density in P. vulgata varie d with wave exposure, but not in any consistent pattern. The other patellid s examined showed variation in pedal mucocyte density, but it was difficult to identify the causes of this variation. Electron microscopy revealed ver y similar microvillose epithelial layers in both P. vulgata and Littorina l ittorea (Linnaeus). Epithelial mucocytes could be seen discharging their co ntents onto the sole. Goblet cells contained membrane-bound packages (simil ar to 0.2-1 mu m) of mucus (or mucin), similar to those found in terrestria l slugs.