Spermiogenesis and sperm ultrastructure of <em>Asetocalamyzas laonicola</em> Tzetlin, 1985 (Polychaeta), an ectoparasite of the large spionid <em>Scolelepis</em> cf. <em>matsugae</em> Sikorsfi, 1994, from the White Sea

Abstract

SUMMARY: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. SIKORSFI, 1994, DEL MAR BLANCO. -La ultraestructura del esperma y la espermatogénesis del poliqueto ectoparásito Asetocalamyzas laonicola Tzetlin, 1985 (Polychaeta) ha sido investigada. Las células masculinas están localizadas libres en el celoma. Los espermatocitos son células grandes de forma irregular cuyos núcleos presentan cromatina condensada en su periferia. El citoplasma de los espermatocitos es granular y presenta alta densidad a los electrones, así como distintas mitocondrias esféricas. Durante el desarrollo inicial, las espermatidas se encuentran agregadas en rosetas de cuatro células. Las espermatidas iniciales presentan una minúscula vesí-cula acrosomal a un lado de la célula, unas pocas mitocondrias redondas y un núcleo denso a los electrones. En su fase más tardía, las espermátidas contienen mitocondrias alargadas, un buen desarrollado acrosoma y un flagelo. El esperma maduro parece estar enebrado con una vesícula acrosomal redonda y una estructura densa a los electrones. El núcleo alargado presenta depresiones posteriores y anteriores. La zona raiz de soporte del acrosoma se encuentra localizada detrás de la vesícu-la acrosomal, en una invaginación anterior del núcleo. Seis mitocondrias alargadas rodean el flagelo y forman la pieza central del esperma. Un centriolo único descansa en la depresión posterior del núcleo. La parte central del flagelo posee un patrón normal (9+2x2). Probablemnente la parte terminal de dicho flagaleo está modificada. La estructura del esperma sugiere una fertilización interna u otro tipo de transferencia del esperma muy especializada en A. laonicola.

Spermatogenesis and spermatozoa ultrastructure of two Dipolydora species (Annelida: Spionidae) from the Sea of Japan

“…Among spionids, a short implantation fossa extends 0.8-1.2 m of the nucleus in the polydorins D. bidentata, D. carunculata, D. socialis, P. ciliata, P. neocaeca, P. websteri, P. paucibranchiata (Franzén, 1974;Rice, 1981Rice, , 1992Williams, 2000;present study), and also in S. laonicola and S. benedicti (Rice, 1981;Vortsepneva et al, 2006). A long fossa extends the entire length of the nucleus in P. cornuta, Pseudopolydora sp., and B. hamata (Rice, 1981(Rice, , 1992Rouse, 1988;Reunov et al, 2010), thus the basal body in spermatozoa is situated anteriorly almost beneath the acrosome.…”

“…Such a transformation does not occur in B. hamata (although the four genera are closely related members of the tribe Polydorini), and in S. benedicti (Rice, 1981) (remarkably, both B. hamata and S. benedicti have filiform mature spermatozoa). A deep anterior nuclear fossa houses the maturating acrosome in late spermatids and retains in mature spermatozoa of S. laonicola (Vortsepneva et al, 2006) and S. setosa (Eckelbarger and Hodgson, 2014). The phylogenetic and adaptive significance of the temporary development of anterior nuclear fossa in some polydorins remains unknown.…”

“…(Rice, 1981;present study), Polydora spp. (Franzén, 1974;Rice, 1981;Williams, 2000), B. hamata (Rice, 1992;Reunov et al, 2010), S. laonicola (Vortsepneva et al, 2006), and S. setosa (Eckelbarger and Hodgson, 2014).…”

“…1 (Rouse, 1988, as Tripolydora sp. ), Polydora neocaeca Williams andRadashevsky, 1999 (Williams, 2000), Scolelepis laonicola 2 (Tzetlin, 1985) (Vortsepneva et al, 2006, as Asetocalamyzas laonicola), Boccardiella hamata (Webster, 1879) (Rice, 1992;Reunov et al, 2010), Pseudopolydora paucibranchiata (Okuda, 1937) (Rice, 1992), and Spio setosa Verrill, 1873 (Eckelbarger and Hodgson, 2014).…”

“…(Radashevsky, unpublished). 2 Vortsepneva et al (2006) initially identified the examined worms as Asetocalamyzas laonicola Tzetlin, 1985 (family Calamyzidae) but later recognized them as dwarf males of the spionid Scolelepis laonicola (Tzetlin, 1985) (Vortsepneva et al, 2008).…”