Ultrastructure of the body wall and gametogenesis in Cossura cf. longicirrata (Cossuridae Polychaeta)статья
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Аннотация:There is little information available about the internal anatomy of the polychaete family
Cossuridae Day, 1963. In the interests of clarifjring the systematic position of this group, we
describe the structure of the abdominal body wall, coelomic organization, spermatogenesis and
oogenesis of Cossura cf. longocirrata Webster and Benedict, 1887. There is a spacious coelomic
cavity in the abdominal region unlike the thoracic region of the body, though as in the thorax
there is no outer peritoneal lining. Muscle layers are virtually absent in certain areas of the
abdomen, explaining the tendency for cossurids to disintegrate very easily. Oogenesis in this
species is extraovarian but each oocyte is ensheathed by a few follicle cells. The follicle cells
appear to be of the "inactive" type since they show no microvilli of the outer surfaces, and no
rER or Golgi bodies. Spermiogenesis occurs with synchronously developing clusters of cells
attached to a central cytophore. Mature sperm have a spherical head, a conical acrosome and a
simple midpiece. This morphology is typically seen in species using external fertilization and
thus the sperm are probably classifiable as ect-aquasperm, though this should be confirmed. The
present results do little to help with the systematic placement of the Cossuridae. Further detailed
study of garnetogenesis and other organ systems across the Polychaeta are required in this
regard.