Nabaviella 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 : 446

Nabaviella sp.

Fig. 76 .

Material.—Four calcium phosphatic internal moulds and coatings, SMNH Sp11495–11498, from samples 19/5.5 and 20/1B, Erkeket Formation, Khorbusuonka River, Siberia,

Russia. Lower Botoman stage (correlated with the lower part of Cambrian Stage 4).

Description.—Clavulate spicules consisting of a prominent straight slowly tapering axial ray (shaft), which bears a bulbous swelling ( Fig. 76C arrowed) at presumably proximal end of the spicule, and a star-like disc (umbel) at the other (presumably distal) end. The disc, up to 0.5 mm in diameter, consists of 11–13 short rays slightly flattened proximally and recurved distally. The shaft is up to 1.3 mm long ( Fig. 76C ), circular in cross-section, up to 0.2 mm in diameter at the disc ( Fig. 76A ). A transversally broken spicule ( Fig. 76B 1 ) displays a wide axial canal having a circular cross-section, ca. 0.1 mm in diameter at the disc. There is a short distal knob, probably representing a reduced axial ray on the opposite side of the disc ( Fig. 76A 2 and D 1 arrowed). The moulding surface of the spicule displays an irregular scalloped ornamentation ( Fig. 76B ).

Remarks.— Mostler and Mosleh-Yazdi (1976) figured spicules with 7–11 rays as syntypes of their type species, including a clavulate anchoring spicule with eight curved paratangential rays as the holotype. This microfossil is compared with either chancelloriid sclerites ( Mostler and Mosleh-Yazdi 1976) or with hexactinellid spicules, including hemidiscs ( Mostler 1985), clavules ( Webby and Trotter 1993) and tylodiscs, and demosponge paraclavules ( Reitner and Mehl 1995). All these spicule types, however, are microscleres. Peel (2019) erroneously quoted “ N. gracilis Mostler and Mosleh-Yazdi, 1976 ” as the type species, but there was no such a species in the original paper. Nabaviella spicules can be also morphologically compared to calcareous meroms of radiocyaths. By contrast, meroms lack axial canals and distal knobs but have straight or slightly recurved radiating and bifurcating coplanar rays at both proximal and distal ends ( Zhuravlev and Sayutina 1985).

Figures

Fig. 76. Spicules of Nabaviella sp. from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; samples 20/1B (A) and 19/5.5 (B–D). A. Calcium phosphatic mould of the spicule with the proximal (proximal part of the spicule) shaft and a terminal knob (arrowed in A2) at the opposite surface of the distal disc (distal part of the spicule) consisting of radiating rays (A1), SMNH Sp11495. B. Calcium phosphatic coatings incompletely replicating the proximal surface of the disc with basal parts of the rays and internal axial canal in the spicule, SMNH Sp11496. B1, plain view; B2, lateral view. C. Internal mould of the proximal shaft with terminal proximal swelling (arrow), SMNH Sp11497. D. Calcium phosphatic internal mould of the axial canal and internal cavity of the distal disc and terminal knob (arrowed in D1), SMNH Sp11498. Scale bar: 125 µm (B) and 250 µm (A, C, D).

Fig. 1. Locality maps. A. Map of the Siberian Platform. B. Khorbusuonka River. Localities referred to in the main text: 96-1, 96-2, 96-3, Malaya Kuonamka (MK) and 96-6, 96-7, 96-8, Bol’shaya Kuonamka (BK) rivers, eastern flank of the Anabar Uplift; 3, 11, 15, 19, 20, Khorbusuonka River, Olenyok Uplift; 21, 22, Lena River lower reaches, Ulakhan-Ald’yarkhay Brook; Le, Lena River middle reaches, Tiktirikteekh and Bydyangaya Brooks; Al, Aldan River, between sections “Dvortsy” and Ulakhan- Sulugur. Margin of the Siberian Platform is shown by a dashed line in A.

Fig. 2. Stratigraphic columns of sections 96-1 and 96-2, Malaya Kuonamka River and section 96-8, Bol’shaya Kuonamka River, Siberia, Russia (after Kouchinsky et al. 2011: fig. 2). Arrows with numbers indicate derivation of fossiliferous samples. Botoman Stage is correlated herein with the Cambrian Stage 4, in accordance with Geyer (2019).Asterisk A, indicates occurrences of Davidonia anabarica, Enigmaconus? pyramidalis, Pelagiella sp. 1 and 2, Majatheca tumefacta, Tetratheca clinisepta, “Lenatheca groenlandica”, Conotheca cf.mammilata, Parkula cf. esmeraldina (see Kouchinsky et al.2015a). Asterisk B, indicates occurrences of Anabaroconus sibiricus, Eotebenna viviannae, Kuonamkaella oliva, Leptostega cf. hyperborea, Pelagiella sp. cf. Cambretina mareki, Pelagiella sp. cf. Costipelagiella zazvorkai, Pojetaia dentifera, Protowenella sp., Pseudomyona queenslandica, and Yochelcionella angustiplicata (see Gubanov et al. 2004b and Kouchinsky et al. 2011). Abbreviations: Ac., Acadoparadoxides; An., Anabaraspis; B., Bergeroniellus expansus; P., Paramicmacca; Fm., Formation; H., Homotreta; O-S, Ovatoryctocara–Schistocephalus; T., Triplagnostus.