Fig. 3

Oral mesovesicle/Hatschek nephridium complex and basal laminae. a, b Fluorescent horizontal sections showing nuclei and immunolabeling for basal laminae. Note dissolution of basal laminae on oral mesovesicle (arrowheads in b). c–e Electron micrographs showing transverse sections of developing oral mesovesicle. While primordium of Hatschek nephridium develops basal laminae, oral mesovesicle does not (arrowheads in c). Oral mesovesicle first opens into pharynx without epithelical intercalation (arrowhead in d). Outlet of Hatschek nephridial canal into pharynx (magenta arrowhead in e) and site of oral perforation (green arrowheads in e). f Electron micrographs showing transverse sections of Hatschek nephridium with flagellum and whorl of microvilli from a cyrtopodocyte (cyan arrowhead) and basal laminae (magenta arrowheads). There is no basal lamia around oral mesovesicle (yellow arrowheads). g Magnification of canal of Hatschek nephridium showing two flagella with a whorl of microvilli (cyan arrowheads) and basal lamina between Hatschek nephridium and pharyngeal endoderm (magenta arrowheads). bs, blood sinus; ch, notochord; da, dorsal aorta; ed, epidermis; en, endoderm; Hn, Hatschek nephridium; lld, left lateral diverticulum; omv, oral mesovesicle; ph, pharynx; 2 mm/L, left 2nd myomere;1-2sc/L, left 1st and 2nd somitocoel. Scale bars 20 μm for (a), (b), 5 μm for (c–f), and 2 μm for (g)