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Summary
Light and electron microscopy were used to analyze the morphology and ultrastructure of the spermatozoon of Fissurella nigra and Fissurella picta, two sympatric species of keyhole limpets from the southern Chilean coast. The spermatozoa of both species are of the aquasperm type, typical of species with external fertilization. Each species had its own distinctive spermatic morphology, particularly in relation to size. Proceeding from anterior to posterior, the spermatozoa of both species each consists of an elongated head with a conical acrosome having a deep subacrosomal space and truncated conical nucleus, followed by a midpiece containing five mitochondria associated in a compact ring around the proximal and distal centrioles, and, at the end, a flagellum. The spermatozoon head of F. nigra is almost twice as long as that of F. picta. This difference constitutes the first morphological evidence that the size of the spermatozoon could represent a candidate for the maintenance of reproductive isolation between these two sympatric species.
