Gill structures of Didazoon haoae. (A) Laterally compressed specimen ELI-2010A (external view); internal openings (inhalant apertures) are revealed (red arrowheads) in left gills 1 to 3 by removal of gill cowls; intact left gill slits 4 and 5 show cowls and exhalant apertures (yellow arrowheads). (B) Laterally compressed specimen ELI-JS1001A, viewed from the interior. (C) Close-up image of right gill slit 3 in (B) (boxed area); note the oval inhalant aperture (arrowhead) surrounded by plate-like structures and radiating strands. (D) Schematic horizontal section through the lateral midline of Didazoon, with inferred ventilation of feeding-respiratory currents (dotted blue lines). Abbreviations: Co, cowl-like structure; LG1-5, left gills 1 to 5; M, mouth; Phx, pharynx; Po, gill pouch; RG1-4, right gills 1 to 4; Wf, water flow. Scale bars: 1 cm in (A), (B); 1 mm in (C).