Ascopora birkenmajeri, Nakrem & Błażejowski & Gaździcki, 2009

Nakrem, Hans Arne, Błażejowski, Błażej & Gaździcki, Andrzej, 2009, Lower Permian bryozoans from southern and central Spitsbergen, Svalbard, Acta Palaeontologica Polonica 54 (4), pp. 677-698 : 689-690

Ascopora birkenmajeri sp. nov.

Figs. 7A–F , 8G–H, 10A, C .

1994a? Ascoporella sp. A ; Nakrem 1994a: 80, figs. 13C, 17A–C.

Etymology: The species name is in honour of Professor Krzysztof Birkenmajer (Institute of Geological Sciences of the Polish Academy of Sciences, Kraków) in recognition of his scientific achievements in the geology of Svalbard.

Type material: Holotype PMO 170.913, paratype PMO 170.913.

Type locality: Gipsvika , Spitsbergen, Svalbard .

Type horizon: Wordiekammen Formation, Tyrrellfjellet Member. Permian, Cis−Uralian, late Asselian–early Sakmarian.

Material examined.—Measurements based on 15 zoaria in the following samples: Hyrnefjellet, sample ZPAL Br.12/G15 (thin section PMO 170.899), sample ZPAL Br. 12/H7 (thin sections PMO 170.903A−G), sample ZPAL Br. 12/H8 (thin section PMO 170.949); Gipsvika, thin sections PMO 170.911B, 170.911C, 170.911F, 170.912, 170.913.

Diagnosis.—Robust zoaria with a wide endozone and axial bundle, up to 8 parallel zooecia in the axial bundle.

Description.—Robust branching species of Ascopora with branch diameter verying between 3.75 and 7.00 mm. Exozone width varies between 0.80 and 1.75 mm. There are usually 2 hemisepta present in exozonal zooecial tubes.Variation in branch diameter and exozone width is generally caused by several growth generations. Endozone average 2.50 mm, with an axial bundle varying between 0.75 and 1.25 mm. There are 5 to 8 parallel zooecia in the axial bundle as viewed in parallel section. Zooecial apertures are elongated being 0.24–0.30 mm long and 0.10–0.14 mm wide. Distance between aperture centers along colony is 0.40–0.60 mm and 0.30–0.40 diagonally. There are 3.3 to 5 apertures along colony per 2 mm and 5 to 6.7 diagonally. Acanthostyles are sometimes up to 0.15–0.16 mm in diameter, averaging 0.11 mm. Stylets, 0.02–0.04 mm in diameter, are developed in the walls between apertures ( Fig. 7H ).

Comparison.— A. birkenmajeri is distinguished from all other species in the current study by the diameter of the axial bundle and the number of parallel zooecia in the axial bundle. The endozone shows great variation in diameter, but is on average narrower than the one in A. grandis , and wider than the endozones of the other species described in the current study.

Remarks.—Several growth generations can be observed in many zoaria (170.903A−G). Locally the exozone is developed as solid stereom without apertures, or very small (“dwarfed”) or closed off apertures.

Measurements.—See Table 7.

Stratigraphic and geographic range.—Occurrence on Svalbard: Asselian, middle part of the Tyrrellfjellet Member, Gipsvika, and the Treskelodden Formation, Hyrnefjellet.

Figures

Fig. 7. Lower Permian bryozoans from Hyrnefjellet, Svalbard. A–F. Ascopora birkenmajeri sp. nov. A. Transverse section showing completely regenerated growth (cylindrical self−encrustation). Sample H7, PMO 170.903A. B. Longitudinal section showing central canal with parallel zooecia. Regenerated growth. PMO 170.903H. C. Regenerated growth. Sample H7, PMO 170.903E. D. Sample H7, PMO 170.903C. Colony growth basis (D1) and colony growth basis displaying unusual thich endozonal walls (D2). E. Sample H7, PMO 170.903D. Regenerated growth. F. Tangential section showing zooecial apertures, large acanthostyles between apertures, and a row of small stylets bordering each aperture. Sample Br.12/G15, PMO 170.899. G, H. Timanodictya sp. G. Oblique tangential section. Sample H10, ZPAL thin section. H. Tangential section showing apertures, and scattered small (1) and large (2) tubercles on colony surface between apertures. Sample H10, ZPAL thin section. Scale bars 0.4 mm.

Fig. 10. External views of selected bryozoan growth forms. A, C. Ascopora birkenmajeri sp. nov. A. Cross−sections of zoaria. Hyrnefjellet, sample ZPAL Br. 12/H7, PMO 170.903. C. Large zoarium. Holotype. Gipsvika, PMO 170.913. B. Ascopora sp. Zoarium surface. Hyrnefjellet, sample ZPAL Br. 12/H24, PMO 170.907. D. Rectifenestella nikiforovae (Shul’ga−Nesterenko, 1936). Gipsvika, PMO 170.915B. E–G. Ascopora sterlitamakensis Nikiforova, 1939. E. Oblique cut abnormal thick zoarium displaying regenerated growth (bottom). Hyrnefjellet, sample Br.12/G15, PMO 170.891. F. Oblique longitudinal section of regular thin zoarium displaying zooecial apertures (bottom). Hyrnefjellet, sample ZPAL Br. 12/H4, PMO 170.893. G. Longitudinal section near point of bifurcations displaying thick endozone (dark) and slightly silicified exozone (white). Gipsvika, PMO 170.911 (original for thin sections 170.911D and E). H. Coscinium cyclops Keyserling, 1846. Zoarium surface showing large fenestrules and numerous rows of apertures on branches. Gipsvika, PMO 170.919. Scale bars 5 mm.