Paterimitra sclerites and articulated specimen from the Early Cambrian of the Arrowie Basin, Flinders Ranges, South Australia. Scale bars, (a–d,f–h,j) 200 μm, (e) 10 μm, (i,k) 100 μm and (l) 50 μm. (a,b) SAMP 43311, from WILK/Q, L sclerite: (a) in apical view showing helical twist and (b) in lateral view showing curved base. (c,e) SAMP 43312, from WILK/R, L sclerite: (c) in lateral view showing long, semicircular base and asymmetrically placed apex (indicated by an arrow) and (e) detail of sclerite surface showing polygonal chambers and walls with bubble-shaped vesicles. (d) SAMP 43313, from WILK/R, L sclerite in apical view showing helical twist. (f–l) SAMP 43314, from AJX-N/213, articulated specimen with fused S1 and four L sclerites: (f) posterior view showing deep TN and composite of L sclerites on the left lateral flank; (g) oblique lateral view showing relative position of L sclerites (indicated as (i)–(iii)) on the left lateral flank, note that sclerites ((ii),(iii)) are positioned in a transverse file and partly overlap sclerite (i); (h) anterior view showing swollen S1 sclerite with damaged anterior margin and base of L sclerites coinciding with curvature of anterior sinus; (i) detail of interior surface showing connecting walls between L sclerites and S1 sclerite partly draped by sheet-like shell layers, note that L sclerites ((ii),(iii)) fused relatively early and have a single internal cavity; (j) apertural view of the S1 sclerite showing L sclerites overlapping each other and margin of the S1 sclerite on the right and a single smaller L sclerite attached in a similar position of the left side (indicated by an arrow); (k) detail of the margin of the S1 sclerite with L sclerites attached, note that sclerite (i) overlaps the margin of the S1 sclerite; and (l) detail of L sclerite (ii) showing reticulate ornament and threefold apex.

Paterimitra sclerites and articulated specimens from the Early Cambrian of the Arrowie Basin, Flinders Ranges, South Australia. Scale bars, (a–g, j–p) 200 μm, (h,i) 10 μm and (q) 50 μm. (a) SAMP 43302, from MMF/0.0, pyramidal S1 sclerite, apical view, posterior side down, showing a rectangular cross section and position of SF. (b) SAMP 43303, from MMF/0.0, pyramidal S1 sclerite in posterior view, apex down, showing TN. (c) SAMP 43304, from MMF/0.0, pyramidal S1 sclerite in anterior view, apex down, showing semicircular anterior sinus (AS). (d–f) SAMP 43305, from AJX-M/256, triangular S2 sclerite: (d) dorsal view with (posterior) UF down; (e) lateral view; and (f) view from UF. (g–i) SAMP 43306, from WILK/I, triangular S2 sclerite: (g) dorsal view with UF down; (h) detail of ornament with regular polygonal chambers; and (i) detail of ornament showing walls of chambers degenerated into bubble-shaped vesicles close to sclerite margin. (j) SAMP 43307, from MMF/0.0, articulated specimen with fused S1 and S2 sclerites in posterior view. The posterior flange of the S1 sclerite is damaged and the S2 sclerite is cracked and deformed. Pedicle opening is partly constricted by callous (indicated by an arrow) growing out from margins of the S1 sclerite. (k) SAMP 43308, from AJX-M/262.7, articulated specimen with fused S1 and S2 sclerites in posterior view, exhibiting circular pedicle opening. The surface of the sclerites is poorly preserved and the S2 sclerite is exfoliated, preserving no discernable growth increments. (l,m) SAMP 43309, from spot locality, upper Wirrapowie Limestone, Druid Range, articulated specimen with fused S1 and S2 sclerites: (l) in posterior view showing SF of S1 and UF of S2 forming elongated ‘pedicle’ tube and (m) oblique anterior view showing S2 sclerite fused at an oblique angle relative to S1 sclerite. Note that growth increments are continuous across the anterior border after sclerite fusion relatively early in ontogeny. (n–q) SAMP 43310, from MMF/0.0, articulated specimen with fused S1 and S2 sclerites and a single probable L sclerite (indicated by arrows in (p,q)): (n) in posterior view; (o) in lateral view showing well-developed ‘pedicle tube’ (indicated by an arrow); (p) in apical view showing S2 sclerite fused at an angle relative to S1 sclerite and the position of probable L sclerite behind and lateral to S2 sclerite; and (q) detail showing small probable L sclerite fused to the margin of the S1 sclerite.