ARTICLE

THE ACROSOME REACTION IN MYTILUS EDULIS : I. Fine Structure of the Intact Acrosome

Lumiko Niijima ¹ and Jean Dan Ph.D.¹

¹ From Tokyo Metropolitan University, Tokyo, Ochanomizu University, Bunkyo-Ku, Tokyo, and The Misaki Marine Biological Station, Miura-Shi, Japan.

Miss Niijima's present address is Laboratory of Hard-Tissue Physiology, Tokyo Medical and Dental University, Tokyo, Japan

The intact acrosome of the Mytilus edulis spermatozoon consists of a conical vesicle, the basal side of which is deeply invaginated so that the whole vesicle forms a sheath around a very slender axial rod, about 2.7 µ long, inserted in a tube passing through the nucleus. The annular base of the acrosomal vesical is filled with a homogeneous substance; the outer wall of the vesicle is lined with a somewhat irregular layer of a particulate substance interspersed with very fine tubular elements, and its lumen is nearly filled by a strand of material which extends from the inner tip of the invagination to the apex of the acrosome. The lumen of the invagination appears empty except for the rod and a delicate sleeve-like structure which surrounds it. The plasma membrane of the sperm cell lies in immediate contact with the acrosomal membrane over its whole outer surface. In its general organization, this molluscan acrosome shows a rather close homology with that of the annelid Hydroides.

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This article has been cited by other articles:

• Healy, J. M., Keys, J. L., Daddow, L. Y. M. (2000). Comparative sperm ultrastructure in pteriomorphian bivalves with special reference to phylogenetic and taxonomic implications. Geological Society, London, Special Publications 177: 169-190 [Abstract]  
• Keys, J. L., Healy, J. M. (2000). Relevance of sperm ultrastructure to the classification of giant clams (Mollusca, Cardioidea, Cardiidae, Tridacninae). Geological Society, London, Special Publications 177: 191-205 [Abstract]  

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