ULTRASTRUCTURE OF BIFLAGELLATE SPERMATOZOA IN THE FRESH-WATER CLAM, CORBICULA-LEANA (PRIME)

In contrast to ''primitive'' uniflagellate spermatozoa of marine and f reshwater bivalves, spermatozoa of the freshwater clam, Corbicula lean a (Prime) have two flagella. One flagellum (50 mu m in length) origina tes from each of the two centrioles. The axoneme of both flagella exhi bit the typical 9+2 pattern. On each side of the flagellum is a thin m embranous wing which originates from the plasma membrane of the flagel lum. The sperm head (17 mu m in length) is elongated and tapers with a slight curve. The indistinct midpiece contains a minimum of five mito chondria and a set of centrioles. The mitochondria form a complex stru cture and envelop the posterior end of the nucleus like a calyx. The a ltered morphology of the spermatozoa from C. leana is discussed in rel ation to its specialized mode of reproduction, i.e., hermaphroditic wi th possible self-fertilization and brooding of young.