Fig. 6

Details of gonozooid anatomy and early embryogenesis in Crisiella producta (light microscopy). a Longitudinal section of autozooid with functional polypide (to the left), developing autozooid with a polypide bud (upper right corner) and developing gonozooid in between; gonozooid contains extended membranous sac enveloping nearly empty coelomic cavity and early embryo surrounded by nutritive tissue on its bottom (‘upper cell complex’ in pseudocoel shown by arrows; distal, not yet calcified wall of gonozooid is out of image). a and insert, Early primary embryo surrounded by developing placental analogue (stage corresponding to Fig. 4e). b Gonozooid with late primary embryo and two secondary embryos surrounded by nutritive tissue including several large cells and partly incorporating membranous sac (large pseudocoelomocyte in pseudocoel shown by arrow; gonozooid roof not visible); insert, Gonozooid with primary embryo starting fission (stage corresponding to Figs. 4f and 5c); in both inserts light areas presumably indicate degenerating cells. c Cross-section of gonozooid with primary embryo starting fission; membranous sac is non-recognizable, being incorporated into nutritive tissue (plugged communication pore in interzooidal wall shown by arrow). d Cross-section of the branch with gonozooid in its upper part showing large, yet empty, incubation (coelomic) cavity and the ‘upper cell complex’ in the pseudocoel. In all zooids the pseudocoel is filled with a network of large and irregular, darkly-stained ‘mesothelial’ cells; in b, insert and d membranous sac shown by arrowheads. c, coelom; cw, external cystid wall; e, primary embryo; g, gut; iw, interzooidal wall; ms, membranous sac; nt, nutritive tissue; p, polypide; pc, pseudocoel; pp, pseudopore; t, tentacle; uc, ‘upper cell complex’