Protohertzina sp.

Kouchinsky, Artem, Alexander, Ruaridh, Bengtson, Stefan, Bowyer, Fred, Clausen, Sébastien, Holmer, Lars E., Kolesnikov, Kirill A., Korovnikov, Igor V., Pavlov, Vladimir, Skovsted, Christian B., Ushatinskaya, Galina, Wood, Rachel & Zhuravlev, Andrey Y., 2022, Early-middle Cambrian stratigraphy and faunas from northern Siberia, Acta Palaeontologica Polonica 67 (2), pp. 341-464 : 418-419

Protohertzina sp.

Fig. 56B .

Material.—Single phosphatic sclerite, SMNH X11240 from sample 11/2B, basal Erkeket Formation, Khorbusuonka River, Siberia, Russia. Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2).

Description.—Bilaterally symmetrical, spine-shaped apatitic sclerite, ca. 1.5 mm long fragment, gently curved in the sagittal plane, with oval cross-section and internal cavity. Convex side of sclerite is rounded and smooth. Opposite, longitudinally concave side of sclerite flattened, separated from the convex side by distinct lateral angulations. Wall composed of multiple layers of fibers longitudinally oriented on outer surface of sclerites.

Remarks.—The sclerite is incompletely preserved and its exact affinity is difficult to determine given morphological variability in Protohertzina and absence of basal part.

Phylum, class, order, and family uncertain

Genus Amphigeisina Bengtson, 1976

Type species: Hertzina? danica Poulsen, 1966 ; lower middle Cambrian ; Bornholm, Danmark .

Amphigeisina danica ( Poulsen, 1966)

Fig. 56E .

Material.—Three fragmentary calcium phosphatic sclerites, including figured SMNH X11239, from samples 19/55 and 19/2B, upper Erkeket Formations, Khorbusuonka River, Siberia, Russia. Ovatoryctocara –Schistocephalus and Kounamkites zones, Amgan stage (correlated with the uppermost Stage 4–Wuliuan Stage).

Remarks.—Fragments of slender, gently curved bilaterally symmetrical hollow sclerites with a relatively narrow concave side separated from the opposite convex side by longitudinal carinated angulations. Cross-section broad crescent-shaped. Outer surface smooth. Despite lamination in the wall, growth lines cannot be distinguished, nor fibrous composition of the wall (Bengtson 1976; Kouchinsky et al. 2011), by contrast with such other forms of protoconodonts described from Siberia and elsewhere as Protohertzina , Gapparodus , Gumella, Hagionella , and Phakelodus . Such a difference in biomineralisation suggests that Amphigeisina does not belong to the same clade of animals but probably nektonic ecdysozoans, although its affinity is pending further study.

Stratigraphic and geographic range.—Upper Botoman stage through the upper Kounamkites Zone, Amgan stage (correlated with the Cambrian Stage 4–Wuliuan Stage; Kouchinsky et al. 2011, 2015a, herein), Siberia ( Russia). Cambrian Series 2 to 3 of South and North China ( Qian et al. 2004), Avalonia ( Great Britain; Hinz 1987), Laurentia ( Landing 1974; Peel et al. 2016), Baltica ( Poulsen 1966; Bengtson 1976), and Kazakhstan (Gridina 1991).

Problematic spines

Fig. 56F–I .

Material.—Over ten calcium phosphatic internal moulds and fragments, including figured SMNH X11241–11244, from sample 19/61, uppermost Erkeket Formation, Khorbusuonka River, Siberia, Russia. Kounamkites Zone, Amgan stage (correlated with the Wuliuan Stage).

Remarks.—Internal moulds of straight and longitudinally flattened spines with a rounded to drop-shaped cross-section of the lumen. Walls of the spines were transversely plicated more or less regularly by rugae of varying amplitude. Corrugation appears to be more prominent along one of the narrower sides of the spine. They are asymmetrical and one of the wider sides can be more flattened than the other one, suggesting a dorso-ventral difference in morphology. The fossils can be interpreted as internal moulds of spines of trilobites or other ecdysozoan animals.

Figures

Fig. 56. Sclerites of protoconodonts (A–E) and problematic spines (F–I) from the early and middle Cambrian, Khorbusuonka River, Siberia, Russia; samples 11/2B (B), 19/55 (E), and 19/61 (F–I) from the Erkeket Formation and 19/3B (C) and 19/5B (A, D) from the Kuonamka Formation. A, C. Gapparodus bisulcatus (Müller, 1959), SMNH X 11236 and X11237, respectively.B. Protohertzina sp., SMNH X11240. D. Sclerite tentatively assigned to Gapparodus bisulcatus (Müller, 1959), SMNH X11238.D1, view on the concave side; D2, lateral view.E. Amphigeisina danica (Poulsen,1966), SMNH X11239.F–I. Calcium phosphatic internal moulds of problematic spines with corrugated walls, SMNH X11241–11244, respectively. Scale bar: 500 µm (A–E) and 250 µm (E–I).