Gill system and reconstruction in Vetulicola rectangulata. (A) Laterally compressed specimen ELI-1037A, viewed from the exterior. (B) Enlargement of left gill slits 3 to 5 in (A) (boxed area), showing gill openings (arrowheads; notably gill 3) surrounded by a folded and striated zone. (C) Laterally compacted specimen ELI-1121A. (D,E) Close-up images of left gill slits 3 and 4, respectively, both showing a concentric zone that surrounds the gill pore; a narrow dark line separates the concentric zone into an inner and an outer section; both units possess radial striations. (F) Three-dimensional reconstruction of two adjacent gill slits (external view) with plates, lappets, and overhanging margins of the groove removed for clarity; note the gill pores are surrounded by a concentric zone and located anterior of each pouch, which posteriorly constricts into a trough. (G) Schematic horizontal section through the lateral groove of Vetulicola, with inferred ventilation of feeding-respiratory currents (dotted blue lines); lateral grooves (dashed black lines) can be either open or closed. Abbreviations: Cz, concentric zone; Fp, fin-like process; G, gill slit; Go, gill opening; Ins, inner section; La, lappet; Lp, left plate; M, mouth; Ots, outer section; Po, gill pouch; Tr, trough. Scale bars: 1 cm in (A), (C), (h); 5 mm in (e), (f), (i); 1 mm in (j), (k).