Beklemischev VN 1963 (citation)- Ax P, Doerjes J 1966 (citation)- describes a new species from fresh water belonging to this genus. Oligochoerus limnophilus- note other species are all from Caspian Sea. this is first fresh water Acoel known. Gives definition of genus p 39- and key to species. Discussion of geographic distribution and significance of new species. p 39-41. Dorjes J 1968 (citation)- p 66 notes problems here in systematics. p 89- defines and list species Oligochoerus erythrophthalmus Beklemischev 1963 O. bakuensis Beklemischev, 1963 O. chlorella Beklemischev, 1963 O. conops Beklemischev, 1963 O. melanops Beklemischev, 1963 O. limnophilus Ax & Doerjes 1966 Beklemischev VN 1969 (citation)- Volume II, p 39- notes 2 or 3 pairs of pyriform organs. Henley C 1974 (citation)- p 294 notes Ax P, Doerjes J 1966 (citation) report of granules in sperm. Kolasa J, Faubel A 1974 (citation)- Oligochoerus described in comparison to new fresh water genus Limnoposthia [Bush note: Limnoposthia place in or close to Mecynostomidae]. Faubel A, Kolasa J 1978 (citation)- Oligochoerus described in comparison to new fresh water genus Limnoposthia.
Vitellaria in acoels According to the keys of Doerjes (1968) (citation) and Bush (1984) (citation), Oligochoerus and Polychoerus differ from other acoels in having separate yolk-producing and germ regions in the ovary, something like the vitellaria of other turbellarians. However, this idea comes from mistaken interpretations of histological sections through ovaries in which larger oocytes are highly lobulated; the oocytes are really entolecithal as is true of all acoels and other archoophoran turbellarians. Beklemischev (1963) (citation) points out this error (as it appeared in Lohner (1910) (citation), as well as in other papers on these genera, including Costello & Costello (1938a,b) (citation) (citation)). On p. 63, he writes [translated from the Russian by Anatoly Petrov]: 'In mature specimens both ovaries converge toward their posterior ends, forming a ring as in Avagina incola (Lieper, 1904). In the last phases of the period of growth, the oocytes form numerous processes like lobopodia of amoebae. The mature egg is round. Immediately behind the pharynx, the oogonia become covered by the envelope of the flat parenchymal sells, and further posteriorly they are submerged in the common stroma of the same kind of cells. The ovaries of P. caudatus have an evidently similar structure; Lohner (1910, table XVI, fig. 9) mistook the whole set of lobated processes of the mature oocyte for the special vitellarium.' In the caption to Figure 3 showing part of the ovary in O. conops (see image under that species name in this database), Bekelmischev writes 'G [4th part]. Oocyte at end of period of growth with long processes. The cytoplasm is overfilled with inclusions. The nucleus has a large nucleolus. Around it are nuclei of young oocytes, the cell bodies of which are not depicted.'
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