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Fig. 2 | BMC Biology

Fig. 2

From: The visual pathway in sea spiders (Pycnogonida) displays a simple serial layout with similarities to the median eye pathway in horseshoe crabs

Fig. 2

Protocerebral sense organs and their connection to the brain in E. spinosa. A Micro-CT scan, frontal view. Left half: external view of the ocular tubercle and underlying cephalon region. Right half: 3D-reconstructed volume rendering of the protocerebral sense organs and their nerves to the brain. The arrow points to the lateral sense organ nerve. Stippled brackets indicate the positions of the extended optical sections (MIP) shown in C and D. B Transverse histological section. C Tubulin (TUB, green) and synapsin (SYN, magenta) immunolabeling with nuclear counterstain and cuticular autofluorescence (AF + NUC, gray), para-sagittal section. Arrowheads point at selected R-cell axon bundles that successively merge into the lateral thickening (stippled lines). Arrows indicate surrounding strands of connective tissues. Double arrows mark tubulin-rich spherical bodies in the anterior soma cortex. D Tubulin immunolabeling (green/magenta) with nuclear counterstain (gray, only in upper image), para-sagittal section. The lateral sense organ and its nerve to the lateral thickening have been segmented and highlighted in a different color. Note that many of the R-cell axon bundles (white arrowheads) have been cut during vibratome sectioning. The black arrowhead points to the nerve connecting to the subepidermal neurite network of the dorsal cephalon (see also Additional file 2: Fig. S1A). The star marks the severed optic nerve extending to the brain. E,F Consecutive histological cross sections through the lateral sense organ. Arrowheads point to fibers of the nerve projecting toward the lateral thickening. Abbreviations: AE – anterior eye; AEL – anterior eye lens; AMT – antero-median tract; BR – brain; BRN – brain neuropil; LO – lateral sense organ; LT – lateral thickening; ONV – optic nerve; PE – posterior eye; RTA – R-cell axons; SVD – sub-visual domain; VN – visual neuropil

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