Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida)

Abstract

Temereva, E.N., Malakhov, V.V. and Yushin, V.V. 2011. Ultrastructural study of oogenesis in Phoronopsis harmeri (Phoronida). -Acta Zoologica (Stockholm) 92: 241-250.The successive stages of oogenesis in Phoronopsis harmeri were examined by electron microscopy methods. During the oogenesis, each oocyte is encircled by vasoperitoneal (coelomic) cells forming a follicle. The previtellogenic oocytes are small cells which accumulate ribosomes for future synthesis; their cytoplasm contains characteristic clusters of mitochondria and osmiophilic particles resembling a germ plasm of other metazoans. The cytoplasm of the vitellogenic oocytes includes numerous mitochondria, cisternae of the rough endoplasmic reticulum, Golgi bodies and annulate lamellae. The synthesis of three types of inclusions was observed: strongly osmiophilic granules (lipid droplets) as a prevalent component, distinctly larger granules surrounded by membrane (proteinaceous yolk) and numerous large vesicles with pale flocculent content. No inclusions which could be unequivocally interpreted as the cortical granules were detected. The surface of the vitellogenic oocytes is covered by microvilli which increase in number and length during development. The oogenesis in Phoronida may be interpreted as follicular because of close association of oocytes with the vasoperitoneal tissue. However, well-developed synthetic apparatus together with a strongly developed microvillous surface and absence of endocytosis indicate a clear case of autosynthetic vitellogenesis. Thus, in phoronids, there is a combination of simply developed follicle and autosynthesis that, apparently, is plesiomorphic character.

Oogenesis in the viviparous phoronid, Phoronis embryolabi

“…Interestingly, the ultrastructure of germ plasm varies among families and even among species within genera. Thus, it is represented by large “clouds” of electron‐dense material in the previtellogenic oocytes of P. embryolabi (our data) but by small electron‐dense granules in such oocytes of P. harmeri (Temereva, Malakhov & Yushin, ).…”

“…This form of follicular oogenesis is well known in a variety of invertebrates including other lophophorates, for example, Brachiopoda (James, 1997; James, Ansell & Curry, 1991; Williams, James, Emig, Mackay, & Rhodes, ). Follicular autosynthetical oogenesis has been suggested to occur in the phoronid P. harmeri for the following reasons: (1) presence of highly developed RER, annulate lamellae, and Golgi apparatus in oocytes; (2) absence of the traces of endocytosis on oolemma; (3) absence of developed synthetic apparatus and glycogenic granules in vasoperitoneal cells; and (4) absence of special contacts between the follicle cells and oocytes (Temereva et al, ).…”

“…Oogenesis has been understudied in Phoronida, and few existing descriptions deal with fragmentary data on various stages of oocytic development. All of them were made using histological method (summarized in Temereva, Malakhov, & Yushin, 2011). The first and only detailed study of oogenesis that includes ultrastructural data is that of Phoronopsis harmeri (Temereva et al, 2011).…”

A Microsporidian Infection in Phoronids (Phylum Phoronida): Microsporidium phoronidi n. sp. from a Phoronis embryolabi

“…1D-F) that nurses the developing oocytes (Temereva 2017) and embryos (Temereva and Malakhov 2016). The vasoperitoneal cells arise from mesodermal cells of the trunk lining, which compose the walls of the blood vessels, and form follicles around oocytes (Temereva et al 2011). In the vasoperitoneal epithelial layer, individual cells are connected with each other and with developing oocytes via desmosomes.…”

Structure of the ovary of the articulate brachiopodHemithyris psittacea(Rhynchonelliformea, Brachiopoda) with special reference to connective tissue pillars

“…Cells of a similar structure were found in the brachiopods Calloria inconspicua and Lingula anatina, but in these species they are a part of the epithelium covering the genital lamellae (Williams et al, 1997). The parenchymal tissue bears some similarities to the vasoperithoneal tissue of phoronids which is also associated with developing gametes and serves for their nutrition (Selys-Longchamps, 1907;Temereva et al, 2009).…”