Histochemistry of the Bucco-Oesophageal Glands ofMytilus Edulis: The Importance of Mucus in Ingestion

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Abstract
Histochemical techniques were used to investigate the possible role of the buccooesophageal glands in the blue mussel, Mytilus edulis L. (Mollusca: Bivalvia). No activity was observed for any of the eight major digestive enzymes tested; however, the glands contained large amounts of both neutral and acid mucopolysaccharides. These results confirm the importance of mucus in the ingestive process in M. edulis, and do not support the hypothesis of ingestion of particles suspended in water alone.Until recently it was thought that the Bivalvia were the only class of molluscs in which some type of secretory gland of extracellular digestive function in the bucco-oesophageal region was totally absent (Table 1). However, in a study of the mode of particle ingestion in five species of suspension-feeding bivalves, an extensive glandular complex was reported in the bucco-oesophageal region of Mytilus edulis L. only (Beninger et al., 1991). Although these glands were observed to liberate secretions into the oesophageal lumen, it was not known whether they performed any digestive function.