Ascopora sterlitamakensis Nikiforova, 1939
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publication ID |
https://doi.org/ 10.4202/app.2008.0078 |
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persistent identifier |
https://treatment.plazi.org/id/03A47E57-7E69-A10A-C766-FD11495CFB78 |
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treatment provided by |
Felipe |
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scientific name |
Ascopora sterlitamakensis Nikiforova, 1939 |
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Ascopora sterlitamakensis Nikiforova, 1939 View in CoL
Figs. 6H–K, 8F, K, 10E–G View Fig .
Material examined.—Measurements based on 9 zoaria in the following samples: Treskelen, sample and one thin section ZPAL Br. 12/Cr. 55; Hyrnefjellet, samples ZPAL Br. 12/H4 (thin section PMO 170.893A), ZPAL Br. 12/H8 (thin section PMO 170.904B), ZPAL Br. 12/H11 (thin section PMO 170.896); Gipsvika, thin sections PMO 170.911D, 170.911E, 170.914, 170.928, 170.945.
Description.— Ascopora with cylindrical bifurcating branches of varying diameter (2.25–4.75 mm). Exozone about 0.40– 1.20 mm wide, axial bundle of parallel zooecial tubes 0.75–1.00 mm in diameter containing 6–7 parallel tubes as observed in longitudinal sections. Two proximal hemisepta are usually present in zooecial tubes in exozone. Apertures elongated oval, sometimes slit−like, 0.26–0.32 mm long and 0.09–0.15 mm wide. The apertures are arranged in rows with ridges between; 3.1–4.5 per 2 mm along colony and 5.9–6.7 diagonally. Distance between apertural centers longitudinally average 0.50 mm. Two large acanthostyles are present adjacent to each aperture. A row of stylets, as observed in shallow tangential section, is present on the ridges between apertural rows. Zooecial wall in exozone is 0.13–0.14 mm in thickness; endozonal wall about 0.010 mm.
Remarks.—Nikiforova’s original material was re−investigated by Morozova and Kruchinina (1986) and the identification herein is mainly based on their revision. Accordingly, A. sterlitamakensis is distinguished from A. magniseptata in having larger and more spaced apertures, a wider axial bundle of parallel zooecia, and also acanthostyles of greater diameter.
One 20 mm long specimen was identified with growth basis preserved, but no visible hard substrate ( Fig. 6K). A possible hard substrate may have been dissolved or lost otherwise, or more likely, this specimen grew in a soft bottom sediment. This unusual preservation indicates deposition in calm lowenergy waters.
Measurements.—See Table 4.
Stratigraphic and geographic range.—Occurrence on Svalbard: Asselian, middle part of the Tyrrellfjellet Member, and the Treskelodden Formation. Sakmarian of Timan−Pechora and the Urals, Russia ( Morozova and Kruchinina 1986).
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