Fig. 4
From: Three in one: evolution of viviparity, coenocytic placenta and polyembryony in cyclostome bryozoans
Details of autozooids in Crisiella producta (light microscopy). a Longitudinal section of autozooid with functional polypide (atrial sphincter shown by white arrow, ‘upper cell complex’ by asterisks, attachment organ by arrowheads, and walls of membranous sac by black arrows). b Longitudinal section of distal tip of autozooid showing wrinkled lower part of vestibulum, ‘upper cell complex’ around atrial sphincter (one of its muscles shown by arrowhead) and upper part of the tentacle sheath and membranous sac. c Cross-section of autozooid at the level of atrium. d Cross-section of autozooid at the level of tentacle crown; membranous sac (smaller arrows) surrounds the tentacle sheath (arrowheads); plugged communication pore in interzooidal wall shown by larger arrow. a, atrium; c, coelom; ca, caecum; ci, tentacle ciliature; cw, external cystid wall; g, gut; iw, interzooidal wall; m, mouth; ms, membranous sac; pc, pseudocoel; ph, pharynx; py, pylorus; r, rectum; rm, retractor muscles; t, tentacle; ts, tentacle sheath; uc, ‘upper cell complex’; v, vestibulum