Dianulites rocklandensis Wilson, 1921

Ernst, Andrej & Carrera, Marcelo G., 2022, A cool-water bryozoan association from the La Pola Formation (Sandbian, Ordovician) of Argentine Precordillera, Geodiversitas 44 (20), pp. 563-601 : 570

Dianulites rocklandensis Wilson, 1921

( Figs 5 F-G; 6A; Appendix 1)

Dianulites rocklandensis Wilson, 1921: 47 , pl. 2, figs 1-2.

MATERIAL EXAMINED. — Single colony (three thin sections) CEGH-UNC 27503 a-c.

OCCURRENCE. — La Pola Formation, Upper Ordovician, Sandbian; La Pola creek section near Albardon village, San Juan Province, Argentine Precordillera, western Argentina. Leray and Rockland formations, Upper Ordovician (Sandbian); Canada.

DESCRIPTION

Massive hemispherical colony, 8.5 mm thick in its central part and 20 mm wide at its base. Secondary overgrowth not observed. Exozone indistinct. Autozooecia long, prismatic, growing from epitheca. Autozooecial apertures polygonal. Diaphragms straight, rare to common in endozone, common in exozone. Autozooecial walls indistinctly granular, irregularly thickened, 0.015 -0.040 mm thick. Maculae not observed.

COMPARISON

The present material is similar to Dianulites rocklandensis Wilson, 1921 from the Ordovician (upper Sandbian) of Canada. This species, as described byWilson (1921), developed branched ramose colonies. However, Kang (2017) mentioned also hemispheric colonies of this species found at the type locality. Dianulites rocklandensis differs from D. microcellatus Astrova, 1945 from the Upper Ordovician of Urals in larger autozooecial apertures (0.24-0.36 mm vs 0.19-0.28 mm in D. microcellatus ).

Figures

FIG. 5. — A-E, Xenotrypa argentinensis n. sp.: A, longitudinal thin section, showing autozooecia with diaphragms and vesicles, holotype CEGH-UNC 27523 b; B, C, tangential thin section showing autozooecial apertures, acanthostyles, and vesicles, holotype CEGH-UNC 27523 a; D, E, tangential thin section showing autozooecial apertures,acanthostyles,and vesicles, paratype CEGH-UNC 27521 a; F, G, Dianulites rocklandensis Wilson, 1921, longitudinal thin section,CEGH- UNC 27503 c. Scale bars: A, B, E, G, 0.5 mm; C, 0.2 mm; D, F, 1 mm.