Fig. 11
From: Three in one: evolution of viviparity, coenocytic placenta and polyembryony in cyclostome bryozoans
Details of ultrastructure of fully-formed nutritive tissue in Crisia eburnea (a‒c, e‒g, i, inserts) and Crisiella producta (d, h, j) (TEM). a, b, Contact of two coenocytic ‘elements’ with lobated nuclei and electron-translucent cytoplasm mostly free of organelles and tight (black arrows) and adherens (white arrows) junctions connecting neighbouring plasma membranes; insert, presumed endocytotic vesicles (arrows) in the plasma membrane facing the pseudocoel (here and elsewhere the basal lamina of the former membranous sac shown by arrowheads). c Part of the nutritive tissue with electron-dense cytoplasm and multiple nuclei in between larvae and secondary embryo. d Periphery of the embryo and adjacent part of the nutritive tissue with electron-dense cytoplasm, two nuclei, multiple autophagosomes and other inclusions and RER; insert, tight (black arrow) and adherens (white arrow) junctions connecting neighboring plasma membranes. e Cytoplasmic bridge (white arrowhead) between coenocytic ‘elements’ (tight and adherens junctions indicated by black and white arrows, respectively). f Interdigitations (asterisks) between coenocytic ‘elements’ (adherens junctions indicated by white arrows) (in insert and e and f, the adherens junctions are 50 nm wide). g, h, Solitary cells (arrows) with electron-dense cytoplasm incorporated into the nutritive tissue (basal lamina of the membranous sac shown by arrowheads; presumed endocytotic vesicles in embryonic cells shown by small arrows). i Longitudinal section of the terminal part of gonozooid with folded roof of modified (coenocytic) membranous sac covered by the ‘upper cell complex’ (also with coenocytic structure) (skeletal spines shown by arrows); secondary embryo is recognizable in lower part of image. j Coenocytic ‘upper cell complex’ (to the left) separated by basal lamina from coenocytic membranous sac. e, secondary embryo; ep, epithelial cell; cw, cystid wall; la, larva; m, mitochondrion; mc, ‘mesothelial’ cell; n, nucleus; nt, nutritive tissue; rer, rough endoplasmatic reticulum; pc, pseudocoel; uc, ‘upper cell complex’