Rhabdomeson bretnalli Crockford, 1957

Ernst, Andrej, 2016, Bryozoan fauna from the Permian (Artinskian-Kungurian) Zhongba Formation of southwestern Tibet, Palaeontologia Electronica (1946) 51 (9), pp. 1-59 : 32-34

Rhabdomeson bretnalli Crockford, 1957

Figure 14.4-9 ; Table 19

1957 Rhabdomeson bretnalli Crockford , p. 75, pl. 20, figs. 4-7.

Material. SMF 23.152– SMF 23.157.

Description. Branched colonies with small axial cylinder. Branches 1.6–3.3 mm in diameter. Axial cylinder circular, 0.27–0.80 mm in diameter. Autozooecia budding in a spiral pattern from the axial cylinder, rhomboid in transverse section. Autozooecial apertures oval, arranged in regular diagonal rows. Single macroacanthostyle between each aperture present building a regular rhombic pattern, 0.03–0.07 mm in diameter. Microacanthostyles abundant, arranged in 1–2 rows between macroacanthostyles, 0.02–0.03 mm in diameter. Hemisepta absent. Diaphragms rare. Autozooecial walls laminated, 0.010 –0.015 mm thick in endozone.

Remarks. Rhabdomeson bretnalli Crockford, 1957 is similar to Rhabdomeson xinjiangense Yang and Lu, 1983 from the Baliqliq Group of western Xinjiang, China, but differs from it by the regular presence of four macroacanthostyles surrounding autozooecial apertures instead of 7–10 acanthostyles in the latter species. Rhabdomeson bretnalli differs from R. ofukuensis Sakagami, 1964 from the Permian of Japan in having larger autozooecial apertures (average aperture width 0.17 mm vs. 0.13 mm in R. ofukuensis ).

Occurrence. Lower Permian (Noonkanbah Series and Liveringa Formation); Western Australia. Zhongba Formation, Permian (upper Cisuralian – Guadalupian); Zhongba area of southwestern Tibet .

Figures

FIGURE 14. Thin section photographs of Streblotrypa (Streblascopora) marmionensis (Etheridge, 1926), SMF 23.145 (1 and 2), and SMF 23.148 (3); and Rhabdomeson bretnalli Crockford, 1957, SMF 23.155 (4–6) and SMF 23.157 (7–9). 1, longitudinal section; 2 and 7, tangential section; 3 and 4, branch transverse section; and 5, 6, 8 and 9; branch oblique section.