Heteractinida, Hinde, 1887

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 505-506

Heteractinida indet.

Fig. 72 .

Material.—Hexaradiate spicules with a bunch of partial rays on one side (seven, from sample 7/70, including SMNH Sp 10334, 10336, and 10337, and eleven, from sample K1-3B, including SMNH Sp 10340) and one hexaradiate with a massive perpendicular ray, SMNH Sp 10344, from sample K1-3B; tetraradiate spicules with a bunch of partial rays on one side (one, from sample 7/70; eight, from sample K1-3B, including five ones with a single massive perpendicular ray on the same side, SMNH Sp 10338 and 10343), and polyactinous spicules with short rays with or without one elongated ray (SMNH Sp 10335 and 10339, from samples 7/70 and K1-3B). Several tetraradiate hexactines, including SMNH Sp 10342, from samples 7/70 and K1-3B are also considered here as probably related. Uppermost Emyaksin Formation, Bol’shaya Kuonamka and Malaya Kuonamka rivers; Calodiscus-Erbiella Zone, lower Botoman Stage.

Remarks.—Secondarily phosphatised spicules, presumably of original calcareous composition, with four, six, or more rays. The four-rayed spicules consist of four slender smooth rays with rounded ends diverging at ca. 90° from the base and at 20–30° to the basal plane ( Fig. 72E, J ). The central part of the convex side of the spicules carries several short rays or nodes and, in some, a single longer ray ( Fig. 72J ). The sixrayed spicules occur more often and consist of six slender smooth rays diverging at ca. 60° from the base and at 10–20° from the basal plane ( Fig. 72A, C, D, G, H ). The central part of the convex side of the spicule carries several nodes. The latter type is similar to the spicules of Eiffelia Walcott, 1920 (see e.g., Bengtson et al. 1990) known to appear globally in the Cambrian Stage 3 ( Kozur et al. 2008). In the latter spicules nodes scatteded on the convex side are not as prominent as in the form reported herein, although tetractines are also described from Eiffelia ( Botting and Butterfield 2005) . Polyactinous ( Fig. 72B, F ) and hexactinous ( Fig. 72I ) spicules co-occur in the assemblage discussed herein. Polyactines consist of several short rays diverging from the same center, but one of the rays can be a long rhabd ( Fig. 72B 1 ). Eiffelia has been attributed to stem-group sponges in which the body wall is formed of a single layer of spicules with internal canals and includes smaller tetraradiate spicules (some of them hexactines) in spaces among larger hexaradiate spicules without perpendicular rays ( Botting and Butterfield 2005).

The spicules also resemble those of Conwaymorrisispongia spp. from the Abadiella huoi Zone of Stage 3 of South Australia ( Kozur et al. 2008), but the latter are characterised by eight massive rays instead of the six in our material. In accordance with the morphological terminology used by Kozur et al. (2008), four or six main rays radiating from the base are paratangential, and nodes in the central part represent branching of the distal ray into partial rays, whereas a proximal ray is not developed. In another spicule, the proximal ray is very massive and six massive paratangential rays radiate from its base ( Fig. 72K ). In polyactine spicules, all types of rays can be reduced, but some of the spicules carry a longer proximal ray and four short paratangential rays in a perpendicular plane. Rare phosphatised regular hexacts ( Fig. 72I ) similar in the morphology of individual rays co-occur with the spicules

1

2

discussed above and may derive from the same sponges, although their hexactinellid affinity cannot be excluded.

Figures

Fig. 72. Spicules of heteractinid sponges from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River and Malaya Kuonamka River, Anabar Uplift, Siberia; sample 7/70 (A–D, H), sample K1-3B (E–G, I–K). A. SMNH Sp 10334; plan (A1) and lateral (A2) views. B. SMNH Sp 10335; B1, lateral view; B 2, plan view on the distal end. C. SMNH Sp 10336; plan view. D. SMNH Sp 10337; plan (D1) and oblique lateral (D2) views. E. SMNH Sp 10338; plan (E1) and lateral (E2) views. F. SMNH Sp 10339; general view. G. SMNH Sp 10340; lateral view. H. SMNH Sp 10341; plan view. I. SMNH Sp 10342; lateral view. J. SMNH Sp 10343; oblique view. K. SMNH Sp 10344; lateral view. Scale bar 600 μm.

Fig. 1. Map showing location of sections 1, 3, Malaya Kuonamka River; 6, 7, Bol’shaya Kuonamka River.