Figures and data
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Beretella spinosa gen. et sp. nov. from Member 5 of the Yanjiahe Formation (Cambrian Stage 2), Yichang, Hubei Province, China.
a‒c, Holotype, CUBar138-12. a, Dorsal view showing the external ornament: (five sclerites at the midline in yellow (S1); flanked by two rows of sclerites in blue (S2); large broad-based conical sclerites in two dorsolateral pairs and one antero-posterior pairs in green (S3)); white arrows indicate lateral constriction. b, Right lateral view showing two additional rows of six sclerites (S4 and S5, in light blue and pink, respectively). c, Ventral view showing a large opening that may have accommodated the mouth (see the text) and an empty body cavity. d‒g, CUBar75-45. d, Dorsal view showing a broken S3. e, Micro-CT image, right lateral view displaying S4. f, Ventral view depicting a tiny projection in purple. g, An enlargement of the projection of f. h‒i, Paratype, CUBar171-5. h, Right dorsal view showing S1‒S4. i, Right-lateral view showing S4 and S5. j‒k, Paratype CUBar121-8. j, Dorsal view showing poorly preserved S1 and S2. k, Right-lateral view showing S3‒S5. A, assumed anterior end (see text); ef, exotic fragment; D, assumed dorsal side; L, left; P, posterior end; R, right; tp, tiny spine; V, ventral side. The same abbreviations are used throughout the manuscript including Supplementary materials.
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Beretella spinosa gen. et sp. nov.
a, CUBar99-19, dorsal view showing an ornament S1‒S4. b‒c, CUBar136-9, general dorsal view and details. d, CUBar136-11, dorsal view showing S1‒S5. e‒f, CUBar73-15 general view and details of the cuticular polygonal reticulation in black. g‒j, CUBar128-27. g, general view. h, i, details of outer and inner surface of the bi-layered structure of the cuticular wall as seen in broken conical sclerites. j, Micro-CT section showing possibly sclerite infilling. k-l, CUBar99-18, cuticular fragment, general view and details of large sclerite (central feature represents possible phosphatic infilling). is, infilling sclerite; pr, polygonal reticulation; sb, sclerite base.
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Position of Beretella spinosa in the animal tree based on cladistic analysis.
a-c, artistic three-dimensional reconstructions of Beretella spinosa in the anterolateral (a), dorsal (b), and posterolateral views (c). d, Phylogenetic tree obtained from cladistic analyses using maximum likelihood. Saccorhytus and Beretella join in a clade (new phylum Saccorhytida) resolved as the sister-group of all other ecdysozoans; numbers at key nodes denote probability. Fossil and extant taxa are in italics and bold, respectively. Known fossil record indicated by thicker vertical bars (after (Shu and Han, 2020a)).
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Possible evolutionary scenario to explain the origin and early evolution of ecdysozoans.
a, Summary tree (see Supplementary Figs. 6-9) showing saccorhytids as a sister-group of Cycloneuralia (Nematoida plus Scalidophora) + Panarthropoda; main morphological features of each group listed along each branch. b, Potential evolutionary pathway to evolve Saccorhytida and crown-group Ecdysozoa. Numbers in green, red and blue circles designate pre-ecdysozoan (Spiralia), Saccorhytida and Cycloneuralia, respectively. Light brown gradient (circle) to emphasize ecdysis and sclerite secretion seen as key evolutionary steps. 1, Hypothetical pre-ecdysozoan animal with a ciliated epidermis and glycocalyx. 2, Saccorhytid exemplified by Beretella with a cuticle bearing sclerites. 3, Crown-group ecdysozoan exemplified by a scalidophoran worm with an elongated shape, a differentiated head (introvert) and trunk, sclerites, a through gut, a terminal mouth and abilities to burrow into bottom sediment. Animals not to scale. Abbreviations: a, anus; a?, uncertain status of anus; ci, cilia; cu, cuticle; ec, epidermal cell; gl, glycocalyx (mucous layer); m, mouth; in, introvert; sc, sclerite; se, sediment; TGE, total-group Ecdysozoa. Silhouettes from phylopic.org.