Fig. 5

Developing vasculature and hemoglobin producing cells in Platynereis as revealed by semi-thin sections and TEM. a–j 3D reconstruction of the blood vascular systems of early P. dumerilii juveniles. All reconstructions are made from stacks of semi-thin sections using Fiji TrackEM2 plugin. 4- (a, b), 5- (c, d), and 6- (e, f) segments juveniles of Platynereis dumerilii. a, c, e Ventral views. b, d, f Lateral left views. g, h Single segment of a 25-segment juvenile worm, carrying a pair of appendages (parapodia) in anterior view and dorsal view, respectively. i, j Vascular system in three contiguous segments of a 50-segment sub-adult worm; The same 3D reconstruction is available as a film in Additional file 12. The outside body wall is lined in light blue. The intestine endoderm is in green. All vessel lumens are in red. HPC are in blue. Arrowheads in (e) and (f) label putative degenerative HPC (green). For the sake of clarity, the dense intestinal blood network (or gut blood sinus) is not shown. k–r Ultrastructure of P. dumerilii HPC in a juvenile worm, 25–30 segments. k Transversal semithin section of a mid-body segment in a 25-segment juvenile worm, showing the position of HPC around the transversal blood vessel. l Magnified view of the transversal vessel surrounded by HPC (rectangle selection in k). m Transmission electron micrograph of the overall hemoglobin-producing tissue organization around a transversal blood vessel. n–r Transmission electron micrographs of different parts of the HPC. n Apical part of a HPC, containing nucleus and rough endoplasmic reticulum. o Basal part of the cell with mitochondria, rough endoplasmic reticulum and ferritin granules. p closer view of a hematin vesicle. q Invaginations of the basal membrane (arrowheads) indicating active exocytosis. r Transmission electron micrograph of the degenerating HPC in sub-adult P. dumerilii (about 50 segments); cross-section through the transversal blood vessel at the level of HPC. Notice the cytoplasm, filled by electron-lucent vesicles (arrowheads), the large electron-lucent vesicle (asterisk) and the granulocytes filled with electron-dense and electron-lucent granules. i intestine, ibv intestinal blood vessels, npv nephridial vessels, tbv transversal blood vessels, vbv ventral blood vessel, tbs transverse blood sinus (pygidium), bv blood vessel lumen, dmc muscular cells of the dissepiment, gc granulocyte, nu cell nucleus, coe coelomic cavity, dbv dorsal blood vessel, ecm extracellular matrix (vascular lamina), hm hematin vesicle, fg ferritin granules, hpc hemoglobin-producing cells, mt mitochondria, nu cell nucleus, rer rough endoplasmic reticulum, vnc ventral nerve cord. Scale bars: k, l 50 μm, m 10 μm, n 4 μm, o–q 2 μm, r 10 μm