Turbellarian taxonomic database

Record # 14719
Author
Title
Journal
Raikova O, Falleni A, Gremigni V (1995)
Oogenesis in Actinoposthia beklemischevi (Platyhelminthes, Acoela): an ultrastructural and cytochemical study.
Tissue & Cell 27(6): 621-633
[doi: 10.1016/S0040-8166(05)80018-7
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Abstract / Notes

"The oogenesis of the acoel Actinoposthia beklemischevi can be divided into a previtellogenic and a
vitellogenic stage. Maturing oocytes are surrounded by accessory cells (a.c.) that produce electron- dense
granules, the content of which is released into the space between the oocyte and a.c. and gives rise to a thin
primary egg envelope. The a.c. may also contribute to yolk synthesis by transferring low molecular weight
precursors to the oocyte. Two types of inclusion are produced in maturing oocytes. Type I inclusions are
small, roundish granules produced by the Golgi complex. They have a proteinaceous non-polyphenolic content
which is discharged in the intercellular space and produce a thicker secondary egg envelope. Type I inclusions
represent eggshell-forming granules (EFGs). Type II inclusions are variably sized globules progressively
changing their shape from round to crescent. They appear to be produced by the ER, contain glycoproteins and
remain scattered throughout the cytoplasm in large oocytes. Type II inclusions represent yolk. The main
features of oogenesis in Actinoposthia are: (a) EFGs have a non-polyphenolic composition; (b) the egg envelope
has a double origin and is not sclerotinized; (c) yolk production appears to be autosynthetic. The present
ultrastructural findings are compared with those from other Acoelomorpha and Turbellaria."

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