Early neurogenesis in Callipallene sp. and Pycnogonum litorale . Tubulin labelling and/or nuclear counterstain of embryos of Callipallene sp. (A–C,E), Pseudopallene sp. (D) and Pycnogonum litorale (F,G). Dashed vertical lines mark the VMR. (A) Ventral overview of germ band, Imaris volume. Morphologically left half of the post-cheliforal region is missing (dissection damage). Note bright orange dots of CISs in pre-cheliforal lobes and in parts of the VNE. Open arrowhead indicates immigrating cells of the forming spinning gland. Solid arrowheads mark conspicuous sites of cell immigration lateral to the palpal and ovigeral hemi-neuromeres. (B) Transverse optical section through pre-cheliforal lobe. Arrowheads mark CISs. Arrows indicate apical mitoses. (C,D) Comparison of CIS pattern in walking leg 1 hemi-neuromeres of Callipallene sp. (C, same stage as in A) and Pseudopallene sp. (D, ES 4). Note similar number and arrangement of CISs (arrowheads) and the beginning formation of an invagination in the posterior region (stippled ovals). Arrowhead with question mark in C marks CIS with no potential counterpart in D. The VNE cells of Callipallene sp. are smaller and more numerous. Cross in C marks damaged region. (E) Ventral overview of embryo in advanced stage of neurogenesis, Imaris volume (blend). Arrows mark segmental invaginations of the ovigeral and the four walking leg neuromeres. (F,G) Overviews of the VNE of P. litorale, stage 4 according to Machner and Scholtz , horizontal 2D projection of curved composite optical sections. Note numerous tubulin-labelled apical spots in (F). The apical VNE of the embryo has a remarkably low number of cells (as indicated by the few nuclei in G). Less intensely stained lipid drops (embryonic yolk) are interspersed between the nuclei.