The structures of exhalent orifice, ctenidium and labial palp of the Mediterranean blue mussel Mytilus galloprovincialis were examined. The exhalent orifice was complicated double structure with elliptical form. The ctenidium showed the homorhabdic filibranch type. The near by filaments were connected mutually with the microvilli of the ciliary disk, composed of collagen fiber. The ordinary filament was equipped with the frontal cilia, the laterofrontal cirri and the lateral cilia. The food groove was the structure that each ordinary filament wound circularly, and the ordinary filaments on the bottom of the food groove were fixed with the ciliary disk. Each labial palp stretched in wing-shape to the outer side of the ctenidium. There was no junction between the ctenidium and the labial palp.
Mediterranean blue mussel
ctenidium
exhalent orifice
food groove
labial palp
ordinary filament