Fig. 1

The amphipod Parhyale hawaiensis and gross morphology of its nervous system. a Male and female of P. hawaiensis in precopula. b Orthoslice at the mid-level of the brain based on microCT analysis. The brain (yellow) is situated right between the compound eyes in the dorsal part of the head. c 3D reconstruction of the brain based on microCT analysis (light grey: optical system, yellow: neuropil, purple: organ of Bellonci, dark grey: somata) in anterolateral view (C1), frontal view (C2) and lateral view (C3). The red line displays the neuraxis of the brain with red dots indicating the roots of associated nerves to sensory organs and appendages to signify the arrangement of proto-, deuto-, and tritocerebrum. An interactive 3D PDF is available as supplement (Additional file 4). d 3D reconstruction of the central nervous system (yellow) in anatomical context based on microCT analysis in lateral view. The central nervous system is located ventrally and bent dorsally, anterior to the subesophageal ganglion. Inset (bottom right corner in B) shows position and orientation of depicted section in the brain. Abbreviations: I-III segmental ganglia of the pleosome, IV-VI fused ganglion of the urosome, a1 antenna 1, a1nv antenna 1 nerve, a2 antenna 2, a2nv antenna 2 nerve, br brain, cb central body, dcc deutocerebral commissure, dcl deutocerebral chemosensory lobe, ec esophageal connectives, es esophagus, g1–7 segmental ganglia of the pereon, gn2 second gnathopod, hn/tm hemiellipsoid body/ terminal medulla complex, la lamina, lan lateral antenna 1 neuropil, lo lobula, me medulla, obe organ of Bellonci, om ommatidia, p1–7 pereopods 1–7, pl1–3 pleopods 1–3, seg subesophageal ganglion, tc tritocerebrum. Scale bars: (a, d) 1 mm, (b) 200 μm, (c) 150 μm