Spermiogenesis and sperm ultrastructure of Asetocalamyzas laonicola Tzetlin, 1985 (Polychaeta), an ectoparasite of the large spionid Scolelepis cf. matsugae Sikorsfi, 1994, from the White Seaстатья
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Аннотация:The sperm ultrastructure and spermatogenesis of the ectoparasitic polychaete Asetocalamyzas laonicola
Tzetlin, 1985 (Calamyzidae) is investigated. The male cells are located freely in the coelom. The spermatocytes are large
cells of irregular shape; their nuclei have condensed chromatin in the periphery. Spermatocyte cytoplasm is granular and
electron-dense with several spherical mitochondria. During early developmental stages spermatids are aggregated into a
rosette (four cells). The early spermatids have a tiny acrosomal vesicle at one side of the cell, a few round mitochondria at
another, and electron dense nuclei. The late spermatids have elongated mitochondria, a well-developed acrosome and a flagellum.
The mature sperm are threadlike with a round acrosomal vesicle, an electron-dense structure. The elongated nuclei
have anterior and posterior depressions. The supporting root zone of the acrosome is located behind the acrosomal vesicle
in the anterior invagination of the nuclei. Six elongated mitochondria surround the flagellum and form the midpiece of the
sperm. A single centriole lies in the posterior depression of the nucleus. The middle part of the flagellum possesses a normal
(9+2x2) pattern. Probably, the terminal part of flagellum is modified. The sperm structure suggests internal fertilization or
another type of specialized sperm transfer in A. laonicola.