Abstract Feeding (filtration) activity and filtration rate were determined in Solen cylindraceus subjected to a variety of natural seston concentrations (5–500 mg 1 −1). At concentrations 5–100 mg l −1 animals spent approximately 90% of the submerged periods filtering (filtration rate ca. 20 ml min −1). Above these seston concentrations filtration activity declined, until at 500 mg 1 −1 animals were active for only 30% of the time (filtration rate ca. 10 ml min −1). At seston concentrations below 50 mg 1 −1 pseudofaecal production was minimal (<10 mg h −1). Between 100 and 500 mg 1 −1 the amount of pseudofaeces produced increased significantly to about 45 mg h −1. The formation and dissolution of the crystalline style and activity of the digestive gland was investigated in animals under natural conditions. The volume of the crystalline style was constant at all phases of the tidal cycle, and it was estimated that the style was completely replaced every 48 h. However, the rate of style production was greater during flood tides. Histological sections of the digestive glands did not reveal any change in the appearance of the digestive cells.