Zhanatellidae, Koneva, 1986

Hansen, Jesper & Holmer, Lars E., 2011, Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen 3076, Zootaxa 3076 (1), pp. 1-122 : 33-34

Zhanatellidae indet.

Pl. 5, Figs. 5–10

Material. Two fragments of ventral valves and one possible dorsal valve from samples JH-29 and JH-157. The figured specimens are TSGF 16787 and TSGF 16788.

Description. Shell slightly convex, small and thin-walled, with acuminate egg-shaped outline. Largest specimen 3.4 mm long and 2.3 mm wide. Macro-ornamentation of fine growth lines, partly developing weak rugae distally. Micro-ornamentation weak near larval shell but strongly developed elsewhere. Lateral micro-ornamentation consisting of radial rows of transversely oval grooves or pits, 3–5 µm wide and 1–2 µm long. Median micro-ornamentation of moderately dense circular pits, about 1–2 µm long.

Umbo not emarginated. Ventral pseudointerarea elevated above and not merging with valve floor but declining toward it. Flexure lines weak. Inner propareas with slightly convex posterolateral margins. Pedicle groove shallow, triangular, increasingly divergent in anterior direction and slightly elevated on a platform. Visceral area not thickened; muscle scars obscure. No pitting on valve floor.

Remarks. The micro-ornamentation of this species most resembles that of the genus Hyperobolus . However, the strongly elongate outline of the shell, and the well-ordered micro-pitting becoming strongly elongate laterally is not typical for the genus. For these reasons we cannot at present assign the specimens to that genus with any confidence. Compared to the species assigned to Hyperobolus , it most resembles H. andreevae ( Popov & Holmer, 1994) from the Floian of the South Urals. The micro-ornamentation of that species also consists of circular pits medianly, becoming transversely oval laterally. H. andreevae is distinguished by its subcircular outline, poorly ordered micro-pitting and irregular radial plications. The type species, H. feistmanteli ( Barrande, 1879) , is thick-walled and broadly subtriangular, with a thickened visceral area. H. fragilis Holmer, Koneva & Popov in Holmer et al., 1996 from the Darriwilian of southern Kazakhstan is thin-walled and has a ventral pseudointerarea much like that of the Spitsbergen species. It is distinguished by its radial plications, rounded umbo, L/W ratio of about 1.15 and strongly defined flexure lines. H. mootwingeensis ( Fletcher, 1964) from the Floian of New South Wales, Australia [redescribed by Percival & Engelbretsen (2007)] is distinctly subtriangular, moderately thick-walled and much larger. H.? thompsonensis Percival in Percival et al., 2009 from the Darriwilian of New Zealand has a markedly more obtuse umbo, is nearly as wide as long and has much more pronounced growth lines.

Occurrence. 108 and 113 m above base of Olenidsletta Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.