The spermiogenesis and the early spermatozoa of <Emphasis Type="Italic">Armorloricus elegans</Emphasis> (Loricifera,Nanaloricidae) |
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Authors: | Iben Heiner Kristine Johanne Kürstein Sørensen Reinhardt Møbjerg Kristensen |
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Institution: | 1.Invertebratezoology Group, Zoological Museum, Natural History Museum of Denmark,University of Copenhagen,Copenhagen ?,Denmark |
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Abstract: | The spermiogenesis consisting of five spermatid stages and the early spermatozoon has been investigated in Armorloricus elegans (Loricifera) with the use of transmission electron microscopy. The male reproductive system consists of three parts; testes,
vasa deferentia and seminal vesicles. Caudally, the two seminal vesicles merge together in a ciliated duct and the excretory/gonadal—and
digestive systems continue through the recto-urogenital canal, which opens via the lateral gonopores and the temporarily closed
anal system. Spermiogenesis mainly occurs in the testes, whereas further maturation of the late spermatids and early spermatozoa
occurs in the vasa deferentia and seminal vesicles. A maturation gradient (from spermatocytes to spermatozoa) is found from
the posterior peripheral part of the testes to the anterior periphery and then centrally. During spermiogenesis the round
nucleus becomes more osmiophilic and condensation of chromatin occurs. Later the nucleus elongates until it becomes rod-shaped
in the early spermatozoa. In the second spermatid stage, a large vesicle is formed by saccules developed from the Golgi complex.
This vesicle develops further and consists of three different osmiophilic parts with some crystal-like structures inside and
is on the outside almost entirely surrounded by thick striated filaments. In the mid-piece the flagellum has a typical 9 × 2 + 2
axoneme and the two mitochondria are fused into a single sheet surrounding the flagellum. In the early spermatozoon stage
an acrosomal-like cap structure with an acrosome filament appears proximal to the protruded rod-shaped nucleus. This cap is
not formed by the Golgi complex and therefore might not be a true acrosome. Comparing the early spermatozoa of A. elegans with other cycloneuralians has shown some similarities with especially Kinorhyncha and Priapulida. These similarities are
thought to be plesiomorphic. |
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