Halkieria proboscidea ( Meshkova, 1969 )

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 : 387-390

Halkieria proboscidea ( Meshkova, 1969)

Fig. 33 .

Material.—Several tens of phosphatised sclerites and calcium phosphatic internal moulds, including figured SMNH X11044–11059, from samples 11/2B, 11/16.05, 11/16.1, 11/16.5, basal Erkeket Formation, Khorbusuonka River, and samples 21/21 and 21/22, Tyuser Formation, Lena River. Siberia, Russia; Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2).

Description.—Cultrate sclerites, 2.5–3.5 times longer than wide, with a broadly triangular cross-section, void axial inner part (lumen) and coalescent lateral zones. Lumen represented by internal moulds, 2–3 times narrower than the blade of sclerite, rounded at the base of sclerite and becoming lenticular towards the apex. Lateral zones house blind channels running parallel to each other and perpendicularly to the respective sclerite margin. Sclerites are slightly sigmoidally curved in lateral view, with dorsally directed distal end and can be slightly helically twisted. Dorsal surface divided by a well-defined median ridge into two almost bilaterally symmetrical sides with 3–4 less prominent parallel longitudinal ridges each, as well as faint striation subperpendicular to the longitudinal sculpture. Basal part rounded triangular in the plan view, extended and deflected ca. 90° with respect to the blade of sclerite. Oval foramen corresponds to ca. 1/4 of the basal part width. Foramen is delimited by a concentric buttress and situated in the middle of basal part.

Palmate sclerites are 0.6–2.0 mm long and deflected ca. 90° at the basal part. They are slightly twisted, have a narrow lenticular cross-section and a pointed apex. A slit-like foramen is situated at the basal end of sclerite delimited by a concentric buttress. Rough and frequent transversal ridges of growth increments are situated on the deflected basal part of sclerite. Blade is slightly arcuate longitudinally, carries a medial low ridge and several faint parallel ridges on the dorsal surface. The surface of the sclerite is covered with transversal growth lines and flattened tubercles.

Remarks.—Apparently conspecific cultrate sclerites were described by Kouchinsky et al. (2017) as Halkieria sp. B , represented by narrow internal moulds from the lower Emyaksin Formation on the eastern flanks of the Anabar Uplift in Siberia. Palmates of the species are probably represented by Halkieria sp. type C (Kouchinsky et al. 2017). Similar cultrate and palmate forms are described by Parkhaev and Demidenko (2010) and Devaere et al. (2013) from the Cambrian Stage 2 of South China and France, respectively, where they are attributed to Halkieria sacciformis ( Meshkova, 1969) . Herein we infer that Sachites proboscideus Meshkova, 1969 , represents internal moulds lumen) of cultrate sclerites ( Meshkova 1974: pl. 25: 1, 2) and Sachites sacciformis represents palmates and cultrates of the same species. Meshkova (1969) first described both forms in the same publication from the Tommotian stage of Siberia. The system of canals in sclerites of Halkieria proboscidea and other sachitids is interpreted to be homologous with the aestetes of the Aculifera (Bengtson 1992; Vinther and Nielsen 2005; Vinther 2009; Peel 2020).

Stratigraphic and geographic range. —Cambrian Stage 2, Siberia, South China, and France.

Figures

Fig. 33. Sclerites of sachitid Halkieria proboscidea (Meshkova, 1969), from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; samples 11/16.05 (A, C, D, H, J, K, M, N), 11/2B (B, E, F, I, L, O), 11/16.1 (G). A–K. Cultrate sclerites, SMNH X11044–11054, respectively. A1, oblique lateral view; A2, oblique view on the upper surface of sclerite; A3, oblique view on the lower surface of sclerite; B1, C1, K2, views on the lower surface of sclerites; B2, C2, K1, lateral views. F, close-up of the sclerite and its internal mould. G, internal mould. L–O. Palmate sclerites, SMNH X11056–11059, respectively. Scale bar: 1 mm (A2, A3, B, F, G, I), 500 μm (A1, C, D, E, J, K, N, O), and 250 μm (H, L, M).