Polypora aff. voluminosa Trizna and Klautzan, 1961

Ernst, Andrej, 2016, Bryozoan fauna from the Permian (Artinskian-Kungurian) Zhongba Formation of southwestern Tibet, Palaeontologia Electronica (1946) 51 (9), pp. 1-59 : 42-44

Polypora aff. voluminosa Trizna and Klautzan, 1961

Figure 19.1-6 ; Table 26

aff. 1961 Polypora voluminosa Trizna and Klautzan , p. 433, pl. 12, fig. 5, pl. 13, fig. 1, text-figs. 26ab.

aff. 1986 Polypora voluminosa Trizna and Klautzan, 1961 ; Morozova and Krutchinina, p. 106, pl. 40, fig. 2.

Material. SMF 23.184– SMF 23.187.

Exterior description. Reticulate colonies composed of moderately wide branches jointed by moderately wide dissepiments. Autozooecia arranged in 3–4 alternating rows on branches. Autozooecial apertures rounded to oval, 4–5 spaced per length of fenestrule. Fenestrules short, oval. Large nodes regularly spaced on the colony surface.

Interior description. Autozooecial chambers relatively short, generally rhombic to roughly hexagonal in the mid-tangential section. Superior hemisepta well-developed, slightly curved proximally. External laminated skeleton well-developed, traversed by abundant small microacanthostyles. Apparent reproductive heteromorphs in form of isolated zooecia with enlarged distal roofed chambers, occurring on obverse colony surface, 0.19– 0.21 mm in diameter.

Remarks. The present species is similar to Polypora voluminosa Trizna and Klautzan, 1961 from the Lower Permian of Urals. However, that species lacks nodes on the reverse side of the colony. It is similar to P. subvoluminosa Krutchinina in Morozova and Krutchinina, 1986 from the Lower Permian of Arctic, but differs from the latter in having wider branches and larger fenestrules (branch width 0.67–1.02 mm vs. 0.45–0.60 mm in P. subvoluminosa ; fenestrule width 0.53–0.70 mm vs. 0.50– 0.60 mm in P. subvoluminosa ; fenestrule length 1.10–1.50 mm vs. 0.90–1.15 mm in P. subvoluminosa ). Both of these species have well- developed superior hemisepta and a rhombic autozooecial chamber in mid-tangential section. Typical Polypora species have regularly hexagonal autozooecia and usually no distinct hemisepta. Representatives of Paucipora Termier and Termier, 1971 have distinct superior and inferior hemisepta dividing the hexagonal chambers in three parts.

Occurrence.?Lower Permian (Artinskian); Russia (Urals). Zhongba Formation, Permian (upper Cisuralian–Guadalupian); Zhongba area of southwestern Tibet.

Figures

FIGURE 19. Thin section photographs of Polypora aff. voluminosa Trizna and Klautzan, 1961, SMF 23.187 (1–3, and 5) and SMF 23.185 (4 and 6); and Mackinneyella obesa (Crockford, 1957), SMF 23.191 (7) and SMF 23.192 (8). 1 and 2, tangential section branches and fenestrules; 3, tangential section of the reverse side showing nodes; 4, tangential section showing autozooecial apertures and chambers with hemisepta (arrow); 5, tangential section showing autozooecial apertures, chambers and heteromorph (arrow); 6, tangential section showing autozooecial apertures and nodes; and 7 and 8, tangential section showing autozooecial apertures and chambers.