Uptake of Particulate Matter By the Epidermis of the Freshwater Snail Lymnaea Stagnalis

Abstract

The ingestion of particulate matter from the external medium by the epidermis of the freshwater snail Lymnaea stagnalis was studied at the ultrastructural level. Ferritin particles were found to be readily absorbed by the cells of the dorsal head epidermis and the inner mantle epithelium within two min exposure to a solution of colloidal ferritin. The ingested particles enter the lysosomal system and apparently end up in the inert residual bodies. Very little ferritin was absorbed by the outer mantle epithelium. There was no evidence for ingestion of colloidal silver even when the snails were exposed to a colloidal silver suspension for 18 hrs. Histochemical tests for acid phosphatase, an indicator of lysosomal activity, were performed for examination with both the light and electron microscope. Intense activity was found in the dorsal head epidermis and the inner mantle epithelium. Only a moderate reaction was found in the outer mantle epithelium. The reaction products were localized primarily in the lysosomes and the Golgi bodies in the supranuclear region of the epidermal cells. These results suggest that the epidermal cells of L. stagnalis absorb particulate matter from the external medium by pinocytosis and digest this material within the lysosomal system. This absorption might play a role in the nutritional economy of the snails.