Fig. 9

Details of ultrastructure of the secondary embryos and early larvae in Crisiella producta (a‒e, insert) and Crisia eburnea (f‒h) (TEM). a Cross-section of the early secondary embryo surrounded by nutritive tissue. b Peripheral part of the early secondary embryo surrounded by nutritive tissue with folded membrane (asterisks); insert, plasma membrane of embryonic cells with forming coated pit (arrowhead) and microvesicles. c Part of the early secondary embryo starting delamination. d Apical membrane of peripheral embryonic cells showing forming coated pit (arrowhead) and (supposedly) endocytic microvesicles (arrows); adjacent membrane of the nutritive tissue strongly folded. e Partial view of the secondary embryo showing central and peripheral zones during delamination (numerous electron-translucent microvesicles are especially abundant around the ‘inner’ cells). f Periphery of the early ciliated larva surrounded by nutritive tissue with two large round solitary cells (microvilli around basal parts of cilia are clearly visible). g Surface of early larva with glycocalyx (arrows) above microvilli. h Surface of early larva with numerous microvilli, ‘endocytotic’ pits and microvesicles (arrows) between cilia bases. Electron-dense lipid droplets are visible in embryonic and larval cells as well as in the nutritive tissue. c, coelom; e, secondary embryo; la, larva; m, mitochondrion; n, nucleus; nt, nutritive tissue; rer, rough endoplasmatic reticulum