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The decrease of Xenopus egg membrane capacity during activation may be due to endocytosis
No full textThe decrease of Xenopus egg membrane capacity during activation may be due to endocytosis.
No full textThe spermatozoa of three species of Xenotrichulidae (Gastrotricha, Chaetonotida): the two "dunne Nebengeisseln" of spermatozoa in Heteroxenotrichula squamosa are peculiar para-acrosomal bodies
No full textMorphology of the reproductive system and spermatozoa of Mesodasys adenotubulatus
No full textMAR. BIOL
Reproductive system and spermatozoa ultrastructure support the phylogenetic proximity of Megadasys and Crasiella (Gastrotricha, Macrodasyida)
Full text linkThe reproductive system and the spermatozoon of Megadasys sterreri from Lanzarote (Canary Islands, Spain) were studied at structural and ultrastructural levels. The species is a simultaneous hermaphrodite with cross-fertilization and shows paired gonads, the male anterior and the female posterior, and both gametes mature in a caudo-cephalic direction. Sperm ducts converge on the midline and open into a ventral common pore.
Two sexual accessory organs are present in the caudal trunk. A pipe-like frontal organ lies between the ovaries and the caudal organ, and is composed of a long, thin region connected to a large zone containing mature and degenerating spermatozoa. The cigar-like caudal organ is elongate, bulky and is made of an anterior glandulo-muscular region and a posterior muscular one.
Spermatozoa are long, filiform cells formed by an acrosome, a nucleus-mitochondrial complex, and a flagellum. The long acrosome is composed of an apical twisted region and a basal straight
region. The nucleo-mitochondrial complex is formed by a
spring-shaped nucleus surrounding basally the mitochondrion and apically a granular material. The flagellum has a 9x2+2 axoneme, characterized by a dense and prominent central sheath surrounding the central tubules. Megadasys sterreri (Cephalodasyidae) shows the same reproductive layout as Crasiella (Planodasyidae): paired gonads, caudo-cephalic maturation of gametes, sperm ducts converging into a common ventral pore, and two sexual accessory organs. Also the spermatozoa ultrastructure shows two similarities in the two genera: a peculiar prominent central sheath in the axoneme and a similar structure of the basal region of the acrosome. Considering the likely polyphyletic
nature of the family Cephalodasyidae, and the sister-
taxon relationship of Megadasys and Crasiella that emerged
from a recent molecular phylogenetic study, a close relationship between the two taxa appears to be very likely; consequently, we propose to remove Megadasys from the family Cephalodasyidae and affiliate it to the family Planodasyidae
A fresh look at Dinodasys mirabilis (Gastrotricha, Macrodasyida), with focus on the reproductive apparatus and sperm ultrastructure
No full textAdults of Dinodasys mirabilis were studied for the first time. The specimens, collected from the west coast of Sweden, were investigated alive and with electron microscopy. Sexually mature specimens attain a total length of 450-490 μm; the adhesive apparatus is made up of anterior, lateral, ventrolateral, dorsal and posterior tubes; one pair of 'cirrata' type tubes is also present. The reproductive apparatus is hermaphroditic; paired testes extend rearward from the pharyngeo-intestinal junction to 3/4 of the trunk; sperm ducts bend anteriorly at U52 and join together into a common, midventral pore at U33. Two ovaries lie along the sides of the caudal intestine, extending anteriorly from U68. Frontal organ present on the right side of the body, centred a U70; caudal organ absent; a gland organ surrounding the terminal intestine may be present but its homology with other organs in a similar position is uncertain. The spermatozoon is a filiform cell, formed by a long acrosome, a spring-like nucleus and a flagellum. The acrosome is divided into two regions: the anterior-most is thin and corkscrew-shaped, the posterior one is rectilinear; both regions are delimited by a continuous external layer of thick, dense material, that in longitudinal section appears obliquely striated and surrounds a long pile of stout, electron-dense cylinders; the nucleus contains condensed chromatin and is coiled around an elongate mitochondrion; the flagellum possesses a 9x2 + 2 axoneme devoid of striated cylinder. Within Macrodasyida, U-bend sperm ducts and the peculiar ultrastructure of the acrosome are characteristics shared by other Turbanellidae studied so far, providing a foundation for the current systematization of Dinodasys
The unique gravireceptor organs of Pleurodasys helgolandicus (Gastrotricha: Macrodasyida)
No full textThe drumstick-like organs of the marine interstitialgastrotrich Pleurodasys helgolandicus Remane, 1927were studied using optical and electron microscopy, inorder to widen our knowledge of the sensory organs amonggastrotrichs. The drumstick-like sensory organs are paired,symmetrical structures located on the dorsal side of thepost-cephalic region of the body. Each sensory organ isformed by an outgrowth of the lamellar exocuticle coveringthe body surface, and it consists of an elongated, cylindricalhollow stalk surmounted by a hollow bulbous tip, housingin its cavity a dense spherical body. Compared with thethree main sensory structures recognized among Gastrotricha,i.e., mechanoreceptors, photoreceptors, and chemoreceptors,the organization of the drumstick-like sensoryorgan matches that of mechanoreceptors. In particular, wesuggest that the drumstick-like sensory organs of P. helgolandicusare gravireceptor organs, analogous to the orthopteran“plumb bob-like” receptors. This is the firstdescription of a putative gravireceptor organ among gastrotrichs
The spermatozoa of a new species of Xenodasys (Gastrotricha, Macrodasyida).
No full textTWINCO TWELFTH INTERNATIONAL MEIOFAUNA CONFERENCE
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