Hadimopanella knappologica ( Bengtson, 1977 )

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 : 483-485

publication ID	https://doi.org/ 10.4202/app.2012.0004
persistent identifier	https://treatment.plazi.org/id/03C3891D-1512-C232-FCC9-FAF1CBB2FA1F
treatment provided by	Felipe
scientific name	Hadimopanella knappologica ( Bengtson, 1977 )
status

Treatment

Hadimopanella knappologica ( Bengtson, 1977)

Fig. 57 View Fig .

Material.—Hundreds to thousands of individual sclerites, including SMNH X 4784–4797, from samples K1-2B, 1/5, 3/60, 3/61.5, 3/62.5, 3/63.5, 3/65, 6/66.2, 7/55, 7/55.8, 7/60, 7/62, and 7/64. Emyaksin Formation, Malaya Kuonamka and Bol’shaya Kuonamka rivers; correlated with the lower Judomia Zone, Atdabanian Stage – Calodiscus -Erbiella Zone, Botoman Stage.

Description.—Disk-like circular to oval phosphatic sclerites with one side convex and smooth, and the opposite side consisting of a conical surface capped with one or several tubercles. Smaller sclerites with a single or a few tubercles

A 3, close-up of the right part of sclerite in A 2; A 4, close-up of the tuberculated limb in the upper part of A 2; A 5, detail of A 4 enlarged. B. Microdictyon rhomboidale Bengtson, Matthews, and Missarzhevsky, 1986 , paratype, SMNH X 4781 View Materials ; B 2, B 3, general views of sclerite; B 1, close-up of the tuberculated limb in the lower part of B

. Scale bar: 400 μm, except A

, A

, B

, 120 μm; A

, 60 μm.

are circular or slightly oval, 80–100 μm in diameter. The tubercles form a circle, sometimes around a central group of 3–5 others. In larger sclerites, a group of up to tens of closely situated tubercles form a flat surface with a rounded or oval outline parallel to the margin of sclerite, with the latter up to 200 μm in larger diameter. The conical surface is either smooth or covered with a fine granulation and straight and fine radial striae. The two surfaces pass into each other with a distinct angulation, marked in some specimens by numerous short subradial rugae.

Remarks.—Disarticulated button-shaped palaeoscolecidan sclerites without affinity to known palaeoscolecidan scleritomes are usually attributed to the form genus Hadimopanella Gedik, 1977 ( Ponomarenko 2005; Topper et al. 2010; García-Bellido et al. 2013; Barragán et al. 2014a, b). The sclerites described herein fall within the size variation of H. knappologica and are most similar to specimens described by Bengtson (1977). Sclerites from scleritomes of paleoscolecids known from the Botoman Stage of the southeastern Siberi- an Platform show a different sculpture ( Ivantsov and Wrona 2004). H. apicata Wrona, 1982 from the upper Stage 3–Stage 4 of Gondwana and Laurentia is, however, similar in size and morphology to smaller single-tubercle individuals available in the collection, but attributed herein to H. knappologica . The number of tubercles in H. apicata varies from one to four in larger specimens, with the diameter of larger sclerites reaching ca. 150 μm. In addition, sclerites of H. antarctica Wrona, 1987 co-occur with those of H. apicata and would have formed part of the same scleritome ( Topper et al. 2010), although Australian sclerites are significantly smaller (11–26 μm) than those from the type material of H. apicata . For that reason, a preliminary definition of the earliest palaeoscolecid sclerites from the Emyaksin Formation as H. apicata (see Kouchinsky et al. 2012) is here considered untenable. The sclerites are therefore redefined herein as H. knappologica . Similar sclerites are also described from the middle Cambrian Kuonamka Formation, Anabar Uplift by Kouchinsky et al. (2011) and as Hadimopanella aff. Н. oezgueli Gedik, 1977 by Müller et al. (1995). Morphologically similar sclerites of the type species, Hadimopanella oezgueli described from the middle–upper Cambrian of Gonwana and Kazakhstan are probably also available from Siberia (see Geyer et al. 2014). Ranges of morphological variability in both form species are, however, broad and overlap, so that it is not possible to associate them with a single or several natural species ( Barragán et al. 2014a, b).