Fig. 2
From: Cleavage modification did not alter blastomere fates during bryozoan evolution
Overview of M. membranacea development. a Vegetal view of an activated egg becoming spherical (1 hpa). b–i Animal pole is top and vegetal pole is bottom. b 2-cell stage showing higher amount of yolk (y) on the vegetal side (2 hpa). c 8-cell stage with yolk positioned on the inner cytoplasmic portions (4 hpa). d 28-cell stage (6.7 hpa). Large vegetal blastomeres (ib) carry most of the yolk (yellowish color), while less yolk is present in the animal blastomeres (ab). e Anterior view of a mid gastrula stage (16 hpa) with a prominent apical disc (ad), shell primordia (sh), coronal cells (co), the vegetal ectodermal plate (vp) demarcated by a dashed line, and the internalized yolk-rich blastomeres (ib). f Frontal view of a late gastrula stage (24 hpa) after the vegetal ectoderm invaginated (dashed line) and the embryo extended in the animal–vegetal axis. Larval structures begin to be functional by this stage, including the apical organ (ao), shell valves (sh), and corona (co). The cilia of the apical tuft and coronal cells break through the fertilization envelope (arrows) at this stage. g–i Lateral views of the cyphonautes morphogenesis with the larval structures illustrated below each panel. The anteroposterior axis is labeled according to [51]. g A late gastrula stage (24 hpa), (h) an early larva (48 hpa), and (i) a fully functional cyphonautes larva 5 days post activation (dpa). Its gut is filled with the red microalgae Rhodomonas sp, which we add to the cultures as a food source. j–m Vegetal views showing beginning of gastrulation. j 8-cell stage (3 hpa). k 16-cell stage (5.2 hpa). l 28-cell stage (6.7 hpa) with four central vegetal blastomeres (ib). m 90-cell stage with vegetal blastomeres (ib) being internalized (15 hpa). ab animal blastomeres, ad apical disc, an anus, co corona, eo exhalant opening, fe fertilization envelope, gt gut, ib inner vegetal blastomeres, io inhalant opening, is internal sac, mc muscle cell, me mesodermal tissue, mo mouth, sh shell primordium, vb vestibule, y yolk. Scale bars = 20 μm