|
Figure 1. Gill anatomy of Vetulicola rectangulata from Yunnan, China. (A,B) Latero-obliquely compressed specimens ELEL-EJ081561A and ELEL-EJ080255A with internal gill openings. (C,D) Interpretative line drawings of (A) and (B), respectively. (E,F) Details of right gill slits 1 to 4 and left gill slits 1 to 3 in (A) and (B), respectively; internal openings (arrowheads; notably right gill 2 in (E)) are surrounded by a zone of striations and folds. (G) Schematic reconstruction of Vetulicola gill system (viewed from the interior) with plates and lappets flanking the lateral groove removed for clarity, showing two adjacent gill slits with anteriorly positioned apertures. Abbreviations: Cz, concentric zone; Dm, dorsal midline; Fp, fin-like process; Go, gill opening; Lp, left plate; LG1-4, left gill slits 1 to 4; LLg, left lateral groove; M, mouth; Po, gill pouch; RLg, right lateral groove; Rp, right plate; RG1-5, right gills 1 to 5; T, tail; Tr, gill trough. Scale bars: 1 cm in (A) to (D); 5 mm in (E) and (F).
|
|
Figure 2. 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).
|
|
Figure 3. 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).
|
|
Figure 4. Gill anatomy and body-wall musculature of Vetulicola rectangulata. (A) Laterally compressed specimen ELI-SJ0605A, with preserved muscular fibers beneath the plate-like unit; note also the tightness of the lateral groove. (B) Internal view of right gill slit 4 in (A); note the internal opening (red arrowhead) surrounded by striations. (C,D) Enlargement of boxed areas in (A) at left and right side, respectively, showing fibrous structures interpreted as longitudinal muscles, defined by diagenetic iron minerals; note their location beneath the plates and arrangement as continuous bundles (approximately six fibers per bundle) extending almost the entire length of the anterior section; note also the equidistant expansions (arrowheads), interpreted here as corresponding to a column of horizontal muscles. (E) Specimen ELI-0000306, showing inferred muscular imprints represented by longitudinal structures in the anterior section (notably the focused area). (F) Reconstructed horizontal section (membrane in blue, plates in grey, musculature in red), equivalent to section A-A' in (A), demonstrating inferred dynamics of pharyngeal dilation, governed by the collective action of the longitudinal muscle fibers and their horizontal derivatives. Abbreviations: Co, cowl-like structure; Fp, fin-like process; LG, left gill slit; M, mouth; Phx, pharynx; RG, right gill slit; T, tail; Wf, water flow. Scale bars: 1 cm in (A), (E); 1 mm in (B) to (D).
|
|
Figure 5. Gill structures of Yuyuanozoon magnificissimi from Yunnan, China. (A) Holotype, complete specimen CFM00059. (B) Enlargement of left gill slit 2 in (A) (box), showing the actual slit (arrowhead) and posterior radiating structures. (C,D) Close-up images of areas indicated in (B) (box) and that posterior of gill slit 3 in (A), respectively, both showing probable interconnection of radiating structures; these structures appear to represent underlying narrow grooves which may have functioned as part of the vascular system (less likely external gill filaments, as interpreted in [18]). G1-5, gills 1 to 5. Scale bars: 1 cm in (A), (B); 1 mm in (C), (D).
|
|
Figure 6. Evidence for the presence of a pharynx and dorsal/ventral feeding gutters in vetulicolians. (A) Vetulicola monile (ELI-SJ1221A) and (B) Vetulicola rectangulata (ELI-SJ1168A), showing remains of food boluses (arrowed) located along a ventral gutter in posterior region of the pharyngeal cavity. (C,D) Close-up images of boxed areas in (A) and (B), respectively; note that posteriorly the food boluses are in continuity with the intestine within the tail. (E) Heteromorphus longicaudatus (ELI-SJ1247), showing food remains (arrowed) along the ventral side. (F,G) V. rectangulata, specimens ELI-SS004A and SS002A, both showing food remains (arrowed) and rearward constriction of pharynx, indicating site of a putative esophagus. (H,I) V. rectangulata, specimens ELI-EJ05832 and ELI-1033A, both showing an expansion (starred) in proximal region of the intestine, possibly equivalent to a stomach. Abbreviations: Fp, fin-like proboscis; G, gill slit; In, intestine; M, mouth; Mb, membrane; T, tail. Scale bars: 1 cm in (A), (B), (E); 5 mm in (C), (D), (F) to (I).
|
|
Figure 7. Schematic reconstruction of Vetulicola rectangulata. (A) Lateral view. Lappets of left gill 2 to 4 removed to reveal gill openings and surrounding features; pharynx and alimentary canal denoted by dashed line; dorsal and ventral food grooves denoted by dotted lines; gill slits colored in pink. (B) Dorsal view. Semidiagrammatical image depicting the internal arrangement of the gills. The diagram is principally to show the overall arrangement of the gills with respect to the rest of the body. Gill morphology is more complex than the diagramatic depiction provided here, and is illustrated in detail in other Figures.
|