Gill function and mucooyte distribution in Placopecten magellanicus ana Mytilus edulis (Mollusca: Bivalvia): the role of mucus in particle transport

Abstract

In order to elucidate the role of mucus in particle transport on the gdl in suspensionfeeding bivalves, the mucocyte distribution was examined on the frontal surfaces of 2 gill types known to a f e r in structure and function: the heterorhabdic plicate gill of Placopecten maqellanicus (Pectinidae) and the homorhabdic gill of Mytilus edulis (Mytilldae). Microscopic counts of mucocyte abundance were performed both on whole mounts of gill segments and on histological sections stained with alcian blue and Periodic acid-Schiff (PAS). A very clear separation of mucocyte types was observed on the P. magellanicus gill: mixed-secretion mucopolysaccharide (MPS) mucocytes were found mainly in the pnnclpal fllament troughs, while acld MPS mucocytes were found mainly on the crests of the ordinary fllament plicae. This dlstnbutlon corresponds to the functional specialization of these 2 sites as revealed by direct endoscopic observation: feeding (pnncipal fllament) and cleaning (ordinary filaments). A more unlforn~ distribution and a broader range of MPS types was found for the M. eduhs gill, corresponding to the absence of anatomical specialization for the separation of feedlng and cleaning functions in this specles Although M eduljs gill functioning is characterized by the presence of a substantial mucus cord in the ventral groove, no mucocytes are located in this groove. Implications of these and further results are discussed in terms of theories of particle transport on different gill types.