Ultrastructural observations on the male gametes in Austrognathia sp. (Gnathostomulida, Bursovaginoidea)

Journal of Morphology
Alberto Lanfranchi, Alessandra Falleni

Abstract

The male gametes of the gnathostomulid bursovaginoid Austrognathia sp. were investigated by electron microscopy. All stages of sperm development can be observed in the single saccular male gonad, which is enclosed by a relatively thick basement membrane internally reinforced by thin smooth muscle cells. The spermatogonia are situated close to the testicular theca and produce generally separate primary spermatocytes. From secondary spermatocytes onwards, the nuclear envelope is no longer visible. The spermatids develop synchronously in groups of four, in contrast to arthropod and vertebrate spermatogenesis. A single, large nurse cell, or trophocyte, never observed previously, surrounds each spermatid; perhaps it represents an altered germ cell functioning in nutrition. The spermatid nucleus, initially ovoid, lengthens and takes on the shape of a mushroom head extending into a stalk. Three degrees of chromatin condensation are visible. Anteriorly, a palisade-shaped structure is present just over the highly heterochromatic nuclear zone and is considered to have an acrosome-like function. The outer sperm cytoplasm is characterized by a peripheral tubular labyrinth. Axonemal structures have never been found, but centriole-like struc...Continue Reading

References

Aug 1, 1973·Journal of Ultrastructure Research·B W Neill, K A Wright
Jun 1, 1971·The Journal of Cell Biology·B S SpoonerN K Wessells
Oct 1, 1968·The Journal of Cell Biology·W E Foor
Jan 31, 1969·Science·R J Riedl

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Citations

Feb 3, 2005·Biological Reviews of the Cambridge Philosophical Society·Edward H Morrow

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