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Fig. 8 | BMC Ecology and Evolution

Fig. 8

From: Three in one: evolution of viviparity, coenocytic placenta and polyembryony in cyclostome bryozoans

Fig. 8

Early developmental stages of the nutritive tissue surrounding early primary embryo, and microanatomical details of Crisiella producta (ag, i) and Crisia eburnea (h) (TEM). a Early multilayered ‘envelope’ consisting of mononucleated cells with cytoplasm of contrasting electron density (membranous sac is out of view). b Fully-formed multilayered ‘envelope’ of mono- and binucleate cells with thin membranous sac lining on its periphery (here and elsewhere basal lamina of the membranous sac shown by arrowheads). c Partly shown embryo surrounded by the nutritive tissue contacting wall of non-altered membranous sac. d Peripheral part of embryo (left corner) and nutritive tissue surrounded by the free wall of non-altered membranous sac. e Embryo lined by multi- and mononucleated cells of modified membranous sac becoming a part of the nutritive tissue. f Mono- and multinucleated cells in the roof of the membranous sac. g Storage cells in the pseudocoel. h ‘Fine-grained’ areas (arrows) in the ‘mesothelial’ and epithelial cells. i Non-altered wall of the membranous sac with adjoined longitudinal muscle and ring muscle (arrow) embedded in the basal lamina in young gonozooid (large ‘mesothelial’ cell is visible close to longitudinal muscle). c, coelom; cw, external cystid wall; e, primary embryo; ep, epidermal lining of cystid walls; iw, interzooidal wall; m, longitudinal muscle; mc, ‘mesothelial’ cell; ms, membranous sac; nt, nutritive tissue; pc, pseudocoel; sc, storage cell

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