Idmonarachne brasieri gen. et sp. nov., Late Carboniferous of Montceau-les-Mines, France; part (a,c,e) and counterpart (b,d,f). (a,b) Dry in low-angle light, showing dorsal opisthosomal segmentation and surface relief; (c,d) under alcohol, showing leg setae and ventral segmentation more clearly; (e,f) morphological interpretation of fossil. All scale bars 1 mm. II, III, IV, second, third and fourth legs; fe, femur; l, lateral part of tergite; m, median part of tergite; pa, patella; S3–S9, ventral plates 3–9; ti, tibia.
Digital visualization of Idmonarachne brasieri gen. et sp. nov. based on laboratory and synchrotron scans of the fossil. (a–c) Laboratory-based scans. (a) Prosoma in anterior view, and ventral opisthosoma of the specimen, with chelicerae tucked between pedipalps, ventral to the clypeus. (b) Dorsal opisthosoma, and prosoma in posterior view, showing some opisthosomal segmentation. (c) Ventral view of prosoma, leg coxae and cheliceral termination apparent. (d–k) Synchrotron scans. (d–e) Tips of pedipalps showing claw and onychium. (f) Isolated chelicerae in detail, comprising paturon and fang. (g) Lateral view of ventral opisthosoma, ventral plates numbered as described in the text—fourth and fifth lacking spinnerets. (h)–(j) Computed slice images showing the opisthosoma in cross section, posterior right, ventral bottom. Sternal plates are preserved as thin, but continuous pieces of cuticle. (k) Ventral view of opisthosoma, ventral plates numbered—fourth and fifth lacking spinnerets. 1L–4L, first to fourth left leg; 1R–4R, first to fourth right leg; ch, chelicerae; CL, left chelicera; CR, right chelicera; co, coxa; fe, femur; fn, fang; pa, patella; PL, left pedipalp; pn, paturon; PR, right pedipalp; S3–S9, ventral plates 3–9; tc, terminal claw; ti, tibia; tr, trochanter.
Cladistic analysis of the arachnids showing the position of Idmonarachne brasieri gen. et sp. nov. Both a strict consensus of the EW analysis, and a strict consensus of the trees recovered from a pruned dataset at 88 concavity constants, are presented, with the fossil in an identical position under all weighting schemes. See also the electronic supplementary material, SI figure S1.