PERIBUCCAL ORGANS OF PLACOPECTEN-MAGELLANICUS AND CHLAMYS-VARIA (MOLLUSCA, BIVALVIA) - STRUCTURE, ULTRASTRUCTURE AND IMPLICATIONS FOR FEEDING .2. THE LIPS

In order to gain a better understanding of the roles of the peribuccal organs of scallops in feeding, the structure and ultrastructure of the arborescent lips of Placopecten magellanicus and Chlamys varia were examined using histological and electron-microscope techniques. The anatomical and histological characteristics of the lips suggest that they are closely related to the labial palps. The lips are formed of a densely-ciliated, ramified oral epithelium and a sparsely-ciliated epithelium which links the ramified ciliated ridges and entirely constitutes the aboral surface. The differential distribution of the three epithelial cell types (ciliated, non-ciliated, and mucocytes), as well as the ultrastructural characteristics of the ciliated and non-ciliated cells and the secretions of the mucocytes suggest that the arborescent lips play at least four different roles in feeding: (1) as a mechanical shield to prevent the loss of mucus-bound food material in the buccal region due to muscular-driven cleansing and swimming currents; (2) as a trap for food material which is lifted out of the oral groove due to especially strong muscular-driven currents; (3) the consolidation of mucus cords from the strands arriving from the palps and of those which have been disturbed by the cleansing currents; (4) the absorption of any dissolved and colloidal matter which may dissociate from the mucus-particle masses in the buccal region. No anatomical detectors or effectors were observed which would suggest a role in particle selection. © 1990 Springer-Verlag.