Spinofenestella subquadratopora ( Schulga-Nesterenko, 1952 )

Ernst, Andrej, 2016, Bryozoan fauna from the Permian (Artinskian-Kungurian) Zhongba Formation of southwestern Tibet, Palaeontologia Electronica (1946) 51 (9), pp. 1-59 : 37-40

Spinofenestella subquadratopora ( Schulga-Nesterenko, 1952)

Figure 17.6-8 ; Table 23

1952 Fenestella subquadratopora Schulga-Nesterenko, 1952, p. 47 , pl. 9, fig. 5.

1975 Fenestella subquadratopora Schulga-Nesterenko, 1952 ; Gorjunova, p. 84, pl. 19, fig. 3, pl. 20, fig. 1.

1994 Alternifenestella subquadratopora Schulga-Nesterenko, 1952 ; Nakrem, p. 94, fig. 17AB.

2000 Alternifenestella subquadratopora Schulga-Nesterenko, 1952 ; Ernst, p. 97, pl. 21, figs. 3-5.

Material. SMF 23.179– SMF 23.181.

Exterior description. Reticulate colony formed by straight branches joined by wide dissepiments.

Fenestrules oval to rectangular, long, narrow. Autozooecia arranged in two rows on branches. Autozooecial apertures circular, with low smooth peristome; two apertures spaced per fenestrule length. Median keel low, relatively wide, containing large widely spaced elliptical nodes.

Interior description. Autozooecia short, triangular in mid-tangential section; with short to moderately long vestibule in longitudinal section. Axial wall between autozooecial rows strongly zigzag; aperture positioned at distal end of chamber. Superior hemisepta long; inferior hemisepta absent. External laminated skeleton well-developed on both obverse and reverse sides, traversed by small microstyles. Microstyles 0.010 –0.015 mm in diameter. Heteromorphs not observed. Nodes on the reverse side irregularly distributed, 0.035 –0.051 mm in diameter.

Remarks. Spinofenestella subquadratopora ( Schulga-Nesterenko, 1952) is similar to Spinofenestella macronodata ( Sakagami, 1964) from the Lower Permian of Japan, but differs from it in having wider branches (branch width 0.29–0.36 mm vs. 0.21–0.24 mm in S. macronodata ) and larger fenestrules (average fenestrule width 0.33 mm vs. 0.28 mm in S. macronodata ; average fenestrule length 0.46 mm vs. 0.40 mm in S. macronodata ). Spinofenestella subquadratopora differs from S. pulcherrima ( Schulga-Nesterenko, 1941) from the Lower Permian of Russia by having larger nodes on the keel (node diameter 0.08–0.14 mm vs. 0.03–0.06 in S. pulcherrima ) and an irregular distribution of nodes on the reverse side of the colony; the nodes in S. pulcherrima are arranged in regular rows.

Occurrence. Upper Carboniferous, late Gzhelian, lowermost part of the Tyrrelfjellet Member; Spitsbergen. Lower Permian (Sakmarian); Urals, Russia. Trogkofel Formation, Lower Permian (late Sakmarian–late Artinskian); Carnic Alps, Austria. Zhongba Formation, Permian (upper Cisuralian– Guadalupian); Zhongba area of southwestern Tibet.

Figures

FIGURE 17. Thin section photographs of Spinofenestella sp., SMF 23.178 (1–5); and Spinofenestella subquadratopora (Schulga-Nesterenko, 1952), SMF 23. 179 (6–8). 1–3, tangential section of the reverse side; 4–7, tangential section of the obverse side; and 8, mid- tangential section.