Fig. 3

The process of sucker formation on the second arm of S. esculenta during embryonic development. Arms are oriented with distal to the right. a-e Confocal stacks of arms from oral view. Cyan: DAPI; red: phalloidin. Arrows: a long narrow ridge (sucker field ridge) on the arm tip. Arrowheads: the proximal constriction of the sucker field ridge. a St. 24–25 (n = 4). b St. 26–27 (n = 5). c St. 28–29 (n = 4). d St. 34–36 (n = 5). e St. 39 (n = 5). f, g Optical sections of the base of the buds at St. 39, stained with phalloidin (f), or DAPI/phalloidin (g) (n = 5). White dotted frames indicate the gourd-shaped actin localization. h A sagittal optical section at St. 39 (n = 5). i-k Higher magnification of white boxed regions in h. White dotted frames indicate the constricted sucker buds (j) and the primordial sucker with differentiated structures (k). l-r Histological sections in sagittal planes stained with hematoxylin and eosin. Arms are oriented with oral to the bottom. l St. 24–25. j St. 28–29. n St. 37–38. o St. 39. p-r Higher magnification of the primordial suckers at St. 39; distal (p), middle (q) and proximal (r) parts. Brackets indicate the region where epithelial cells composed one layer. Scale bars: 50 μm. Abbreviations: ac, acetabulum; in, infundibulum; n: nerve; p, peduncle