Ascopora grandis Kruchinina, 1973

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 : 688-689

Ascopora grandis Kruchinina, 1973

Fig. 8C–E, J.

Material examined.—Measurements based on 12 zoaria (including material from Nakrem 1994a) in the following samples: Gipsvika, thin sections PMO 170.933, 170.936. See also occurrences listed in Nakrem (1994a: 80).

Description.—Zoarium ramose with thick branches averaging 6.8 mm in diameter. Exozone average 1.08 mm wide; endozone average 4.11 mm in diameter. Axial bundle diameter 1.75–2.35 mm. The axial bundle comprises 9–10 parallel zooecial tubes as viewed in longitudinal section. Zooecial apertures elongated, 0.26–0.36 mm long and 0.12–0.16 mm wide. There are 3.3–3.8 zooecial apertures in 2 mm along colony; 5.6–6.7 diagonally. There are 2–3 hemisepta present in exozonal zooecial tubes ( Fig. 8J). One large acanthostyle is developed in the area between zooecial apertures protruding above colony surface ( Fig. 8E); diameter 0.08–0.13 mm. Small, infrequent pores are also present in exozonal walls. Exozonal walls are generally 0.11–0.12 mm thick as measured between adjacent apertures in tangential section. Endozonal walls are 0.11–0.12 mm thick.

Remarks.—The described specimens compare well with the illustrations and descriptions given by Kruchinina (1973) and Morozova and Kruchinina (1986) in branch diameter and number of parallel zooecia in the central bundle, but the Spitsbergen material has a significantly narrower axial bundle diameter. It should be remarked that the axial bundle was described as containing 15–22 parallel zooecial tubes, but the illustrations given ( Kruchinina 1973: pl. 28: 1c, identical to Morozova and Kruchinina 1986: pl. 22: 1c) display a maximum of 11 parallel zooecia. The number of parallel zooecial tubes counted from these illustrations is actually lower than the minimum figure given in the generic diagnosis of their genus Ascoporella and we have chosen to place this species in Ascopora .

Comparison.— A. grandis is distinguished from A. borealis ( Stuckenberg, 1895) and A. enormis Kruchinina, 1986 (both Artinskian species from Timan) in having smaller branch diameter, and fewer parallel zooecia in the axial bundle. A. grandis is distinguished from all other species in the current study in its wide axial bundle and number of parallel zooecia in the axial bundle.

Measurements.—See Table 6.

Stratigraphic and geographic range.—Occurrence on Svalbard: Late Asselian, middle part of the Tyrrellfjellet Member. Sakmarian (Ilibei Horizon) of Timan−Pechora, Russia ( Morozova and Kruchinina 1986).