Revisiting the scorpion central nervous system using microCT

Abstract

The central nervous system (CNS) of Chelicerata has remained conserved since the Cambrian, yet few studies have examined its variability within chelicerate orders including Scorpiones. The scorpion CNS comprises the prosomal ganglion and opisthosomal ventral nerve cord. We visualize the scorpion CNS with microCT, explore morphological variation across taxa, compare the scorpion CNS to other arachnids, and create a terminology glossary and literature review to assist future studies. Six scorpion species were microCT scanned. Scan quality varied and most structures in the prosomal ganglion could only be observed in Paruroctonus becki (Vaejovidae). Major nerves and the first opisthosomal ganglion were visible in nearly all taxa. We present the most detailed 3D-rendering of the scorpion prosomal ganglion to date. Our results corroborate existing research and find the scorpion CNS to be conserved. Nearly all structures reported previously in the prosomal ganglion were located in similar positions in P. becki, and nerve morphology was conserved across examined families. Despite similarities, we report differences from the literature, observe taxonomic variation in prosomal ganglion shape, and confirm positional variation for the first opisthosomal ganglion. This study serves as a starting point for microCT analysis of the scorpion CNS, and future work should include more distantly related, size variable taxa to better elucidate these findings.

Keywords: Arcuate body; Brain; Central nervous system; Mushroom body; Prosomal ganglion; Scorpions.

Fig. 1

Parasagittal view of prosomal ganglion. Parasagittal view, anterior-posterior axis of the prosomal ganglion in Vaejovidae Thorell, 1876 (A, B), Hormuridae Laurie, 1896 (C), Hadruridae Stahnke, 1974 (D), Chactidae Pocock, 1893 (E), and Buthidae C.L. Koch, 1837 (F). (A) Paravaejovis spinigerus (Wood, 1863); (B) Paruroctonus becki (Gertsch & Allred, 1965); (C) Liocheles australasiae (Fabricius, 1775); (D) Hadrurus arizonensis Ewing, 1928; (E) Uroctonus mordax Thorell, 1876; (F) Centruroides sculpturatus Ewing, 1928. Insets indicate the parasagittal plane in the prosoma for each species. Br brain, Ch chelicera, dME dextral median eye, SbM subesophageal mass, T1 first tergite. Axis indicator abbreviations: A anterior, P posterior. Scale bars = 1 mm.

Fig. 2

Transverse view of the prosomal ganglion. Transverse view, dorsal-ventral axis of the prosomal ganglion in Vaejovidae Thorell, 1876 (A, B), Hormuridae Laurie, 1896 (C), Hadruridae Stahnke, 1974 (D), Chactidae Pocock, 1893 (E), and Buthidae C.L. Koch, 1837 (F). (A) Paravaejovis spinigerus (Wood, 1863); (B) Paruroctonus becki (Gertsch & Allred, 1965); (C) Liocheles australasiae (Fabricius, 1775); (D) Hadrurus arizonensis Ewing, 1928; (E) Uroctonus mordax Thorell, 1876; (F) Centruroides sculpturatus Ewing, 1928. Insets indicate the transverse plane in the prosoma for each species. AB arcuate body, Ph pharynx. Axis indicator abbreviations: A anterior, P posterior. Scale bars = 0.2 mm.

Fig. 3

Central nervous system of Paruroctonus becki (Gertsch & Allred, 1965). 3D-renderings of the central nervous system (CNS) of P. becki in dorsal (A, B), lateral (C, E) and frontal views (D, F), including overview of CNS with the ganglia of the opisthosomal ventral nerve cord (A), prosomal ganglion (B–D) and mushroom body with arcuate body (E, F). AB arcuate body, AC1–AC4 four arcuate body lobes, aPcN anterior pectinal neuropil, Br brain, ChN cheliceral neuropil, CN central neuropil, Dlf dorso-lateral fibre tract, L1 first-order lateral eye neuropil, L2 second-order lateral eye neuropil, Lf longitudinal fibre tract, M1 first-order median eye neuropil, M2 second-order median eye neuropil, MBbr mushroom body bridge, MBc mushroom body calyx, MBp mushroom body pedunculus, MBl1–MBl2 first and second mushroom body lobes, M-AB tract interconnecting the median eye neuropils with the arcuate body, OG1–OG7 opisthosomal ganglia 1–7, PeN1–PeN4 pedal neuropils for legs I–IV, Pcb protocerebral bridge, pPcN posterior pectinal neuropil, PpN pedipalpal neuropil, SbM subesophageal mass, Stb stomodeal bridge, TC transverse commissures, Vlf ventro-lateral fibre tract. Axis indicator abbreviations: A anterior, De dextral, Do dorsal, P posterior, S sinistral, V ventral. Scale bars: (A) = 2 mm; (B–D) = 0.2 mm; (E, F) = 0.05 mm. 3D-renderings available in MorphoSource (https://www.morphosource.org; Project ID: 000592858; DOIs: 10.17602/M2/M593451; 10.17602/M2/M592979; 10.17602/M2/M592982).

Fig. 4

Lateral view of prosomal ganglion and associated nerves. 3D-renderings of the prosomal ganglion and associated nerves in lateral view in Vaejovidae Thorell, 1876 (A, B), Hormuridae Laurie, 1896 (C), Hadruridae Stahnke, 1974 (D), Chactidae Pocock, 1893 (E), and Buthidae C.L. Koch, 1837 (F). (A) Paravaejovis spinigerus (Wood, 1863); (B) Paruroctonus becki (Gertsch & Allred, 1965); (C) Liocheles australasiae (Fabricius, 1775); (D) Hadrurus arizonensis Ewing, 1928; (E) Uroctonus mordax Thorell, 1876; (F) Centruroides sculpturatus Ewing, 1928. aPeNv accessory pedal nerves, aPpNv accessory pedipalpal nerves, Br brain, ChNv cheliceral nerves, LNv lateral nerves, LONv lateral ocular nerves, MONv median ocular nerves, Nl neurilemma, Oes esophagus, OG1 first opisthosomal ganglion, OVNC opisthosomal ventral nerve cord, PcNv pectinal nerves, PeNv 1–4 pedal nerves for legs I–IV, PpNv pedipalpal nerves, SbM subesophageal mass, VS vascular system. Axis indicator abbreviations: A anterior, Do dorsal, P posterior, V ventral. Scale bars = 0.5 mm. 3D-renderings available in MorphoSource (https://www.morphosource.org; Project ID: 000592858; DOIs: 10.17602/M2/M593464; 10.17602/M2/M592973; 10.17602/M2/M592970; 10.17602/M2/M592967; 10.17602/M2/M593461; 10.17602/M2/M592964).

Fig. 5

Dorsal view of prosomal ganglion and associated nerves. 3D-renderings of the prosomal ganglion and associated nerves in dorsal view in Vaejovidae Thorell, 1876 (A, B), Hormuridae Laurie, 1896 (C), Hadruridae Stahnke, 1974 (D), Chactidae Pocock, 1893 (E), and Buthidae C.L. Koch, 1837 (F). (A) Paravaejovis spinigerus (Wood, 1863); (B) Paruroctonus becki (Gertsch & Allred, 1965); (C) Liocheles australasiae (Fabricius, 1775); (D) Hadrurus arizonensis Ewing, 1928; (E) Uroctonus mordax Thorell, 1876; (F) Centruroides sculpturatus Ewing, 1928. aPeNv accessory pedal nerves, aPpNv accessory pedipalpal nerves, Br brain, ChNv cheliceral nerves, LNv lateral nerves, LONv lateral ocular nerves, MONv median ocular nerves, Nl neurilemma, Oes esophagus, OG1 first opisthosomal ganglion, OVNC opisthosomal ventral nerve cord, PcNv pectinal nerves, PeNv 1–4 pedal nerves for legs I–IV, PpNv pedipalpal nerves, SbM subesophageal mass, VS vascular system. Axis indicator abbreviations: A anterior, De dextral, P posterior, S sinistral. Scale bars = 0.5 mm. 3D-renderings available in MorphoSource (https://www.morphosource.org; Project ID: 000592858; DOIs: 10.17602/M2/M593464; 10.17602/M2/M592973; 10.17602/M2/M592970; 10.17602/M2/M592967; 10.17602/M2/M593461; 10.17602/M2/M592964).