Etherella tibetensis, Ernst, 2016

Ernst, Andrej, 2016, Bryozoan fauna from the Permian (Artinskian-Kungurian) Zhongba Formation of southwestern Tibet, Palaeontologia Electronica (1946) 51 (9), pp. 1-59 : 20-22

Etherella tibetensis n. sp.

Figures 9.6 , 10 ; Table 11

zoobank.org/ 1610F4FA-934D-4255-ADF6-1DFF0931FBA1

Etymology. The species is named after its occurrence in Tibet.

Holotype. SMF 23.214 .

Paratypes. SMF 23.215 – SMF 23.223 , SMF 23.230 , SMF 23.231 , SMF 23.267 .

Type locality. Zhongba area of southwestern Tibet (E 83.76894, N 29.93333) .

Type stratum. Zhongba Formation, Permian (upper Cisuralian–Guadalupian).

Diagnosis. Reticulate colonies formed by fused branches; branches bifoliate, lenticular, rounded to oval in transverse section; fenestrules circular to oval; autozooecia arranged in 8–10 rows on branches; lunaria absent; vesicular skeleton scarcely developed, vesicles small; extrazooecial skeleton well-developed; monticules absent.

Description. Studied material represent a bifoliate reticulate colon split in the plane of mesotheca ( Figures 9.6 , 10.8 ). Branches 2.8–5.1 mm wide and 8.0– 10.3 mm thick, rounded to oval in transverse section. Fenestrules circular to oval, 1.6–3.3 mm wide and 2.1–4.0 mm long. Autozooecia tubular, long, rhombically arranged in 8–10 longitudinal rows on branches, lacking on lateral sides of branches; subquadrate, trapezoid to subhemispherical in transverse section at mesotheca; angular shaped in deep tangential section in mid exozone and partially isolated by vesicles. Long and thin hook-shaped superior hemisepta present at the transition between endo- and exozone, curved proximally, club-shaped. Basal diaphragms rare. Mesotheca consisting of granular-prismatic material, straight, 0.02–0.03 mm thick; median tubules present, 0.015 –0.030 mm in diameter; longitudinal ridges absent. Autozooecial walls granular-prismatic, 0.015 –0.040 mm thick. Autozooecial apertures arranged regularly in 9–13 diagonal rows on branches, rounded to oval. Lunaria absent. Vesicular skeleton well-developed, restricted to exozone; vesicles blister-like, low to moderately high with flat to rounded roofs, polygonal in tangential section. Extrazooecial skeleton well-developed, displaying cloudy structure produced by stabshaped elements. Acanthostyles absent. Monticules absent.

Remarks. Etherella tibetensis n. sp. differs from Etherella porosa Crockford, 1957 and E. porosa minor Crockford, 1957 from the Lower Permian (Artinskian–Kungurian) of Western Australia, in having larger and more closely spaced autozooecial apertures as well as an extremely thick extrazooecial skeleton. Etherella tibetensis n. sp. shows intermediate dimensions of colony elements comparable to both Australian species:

Etherella porosa —branch width: 4.0– 5.5 mm;

fenestrule width: 3.0–5.0 mm; fenestrule length:

5.0–7.0 mm; aperture width: 0.13–0.16 mm;

aperture spacing: 0.5–0.7 mm.

Etherella porosa minor —branch width: 2.0–3.3

mm; fenestrule width: 2.0– 2.5 mm; fenestrule length: 2.0– 3.5 mm; aperture width: 0.14 mm;

aperture spacing: 0.50–0.83 mm.

Etherella tibetensis —branch width: 2.8–5.1

mm; fenestrule width: 1.6–3.3 mm; fenestrule length: 2.1–4.0 mm; aperture width: 0.12–0.21

mm (0.17 mm at average); aperture spacing:

0.45–0.66 mm (0.53 mm at average).

The species Coscinotrypa orientalis Sakagami, 1968 from the Permian of Khao Ta Mong Rai, Thailand, may belong to Etherella . It shows oval apertures without lunaria, scarce vesicular skeleton and extensive extrazooecial skeleton. However, the presence of the hook-shaped hemisepta cannot be confirmed on that material because the part of the colony at mesotheca is strongly affected by diagenesis. This species also possesses larger autozooecial apertures (average autozooecial width 0.24 mm vs. 0.17 mm in E. tibetensis ).

Figures

FIGURE 9. Thin section photographs of Liguloclema meridianus (Etheridge, 1926), SMF 23.093 (1), SMF 23.085 (2), and SMF 23.083 (3–5); and Etherella tibetensis n. sp., paratype SMF 23.217 (6). 1 and 2, branch oblique section showing mesotheca, autozooecial chambers with hemisepta and vesicular skeleton; 3 and 4, mid-tangential section showing autozooecial chambers with hemisepta; 5, tangential section showing autozooecial apertures; and 6, transverse section showing extrazooecial skeleton and sparse vesicles.

FIGURE 10. Thin section photographs of Etherella tibetensis n. sp., paratype SMF 23.267 (1), paratype SMF 23.216 (2), paratype SMF 23.219 (3 and 4), holotype SMF 23.214 (5–7), and paratype SMF 23.230 (8 and 9). 1, external view of the colony (split along mesotheca); 2–4, tangential section showing arrangement of autozooecia and wall microstructure; 5–7, oblique section showing hemisepta and mesotheca (arrows); and 8 and 9, branch transverse section showing autozooecial chambers and extrazooecial skeleton.