Fig. 2

Holotype of Helenodora inopinata (FMNH PE29049). a Part and (c) counterpart, from the Francis Creek Shale, Westphalian D, Middle Pennsylvanian. Specimen preserved in lateral aspect and photographed wet under cross-polarised light. b Camera lucida drawing of part shows body outline and outline of limbs, as well as patches of annulated cuticle, shaded in grey. Note the dark patches outside the body margin ventral to limbs 5, 7 and 9. Details of both the anterior and posterior ends are not preserved, despite attempts to excavate the anterior of the counterpart (b) by Thompson & Jones [8]. Numbers refer to walking limbs from anterior to posterior. ann = trunk annulae. Scale bar = 10 mm. High resolution versions of each photograph provided in additional materials (Additional file 2)