Broeggeria obscura, Hansen & Holmer, 2011

Hansen, Jesper & Holmer, Lars E., 2011, Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen 3076, Zootaxa 3076 (1), pp. 1-122 : 34-36

Broeggeria obscura sp. nov.

Pl. 6, Figs. 1 –11; Table 6

Derivation of name. Latin ‘ obscuro ’, obscure; refers to the obscure visceral area.

Holotype. Pl. 6, Fig. 10; TSGF16763 , dorsal valve; 99 m above base of Olenidsletta Member, Valhallfonna Formation, sample JH-15; Profilstranda at Basissletta (N79˚50.886’, E017˚41.893’), Ny Friesland, Spitsbergen.

Material. 492 specimens from samples with A84043, A84080, A84092, A84339 , A84360 a and A84362 a and from samples F2875, F3028, F3475, F3477, F3478, F3485, F3515, F3541, F3542, F3546, F3560, F3561, F3613, F3667, F3675 ½, F3678, F3747, F3748, F3749, F3875, F5237, F5642, TS92.3, JH-12, JH-14, JH-15, JH-31, JH- 35, JH-36, JH-38, JH-41, JH-43, JH-46, JH-49, JH-51, JH-52, JH-54, JH-55, JH-57, JH-129–131, JH-136, JH-140, JH-141, JH-155, JH-157, JH-188 and JH-189. The paratypes are TSGF16761 , TSGF16762 , TSGF16798–16800 , TSGF16936 , TSGF16938 and TSGF17082 .

Plate 6

Broeggeria obscura sp. nov.

Valhallfonna Formation, Olenidsletta Member.

1. TSGF16761 , paratype, impression of ventral valve exterior. 75–103 m above base. Coll. J. Hansen, 17.07.2008, sample JH- 189 .

2. TSGF16762 , paratype, dorsal valve exterior. 86 m above base. Coll. J. Hansen, 21.07.2008, sample JH-157 .

3, 5–6. TSGF16798 , paratype, valve fragment, micro-ornamentation, and detail of micro-ornamentation. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52 .

4. TSGF16936 , paratype, dorsal pseudointerarea and pitted valve floor. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136 .

7. TSGF16800 , paratype, detail of dorsal median groove. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52 .

8. TSGF16799 , paratype, ventral pseudointerarea. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52 .

9. TSGF17082 , paratype, dorsal valve floor. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136 .

10. TSGF16763 , holotype, impression of dorsal valve floor. 99 m above base. Coll. J. Hansen, 18.07.2008, sample JH-15 .

11. TSGF16938 , paratype, detail of ventral pseudointerarea. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136 .

Mirilingula ? svalbardensis sp. nov.

Valhallfonna Formation.

12–13. TSGF16979 , paratype, dorsal and oblique lateral views of dorsal umbo. Profilbekken Member, 17 m above base. Coll. J. Hansen, 19.07.2008, sample JH-25 .

14. TSGF16972 , paratype, dorsal umbo. Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23 .

15–18. TSGF16968 , paratype, ventral umbo, detail of larval shell, detail of postlarval shell, and oblique posterolateral view. Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23 .

19–20. TSGF16969 , holotype, ventral pseudointerarea. Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23 .

Diagnosis. Subtriangular to subcircular Broeggeria with nearly equidimensional outline and obscure visceral areas; dorsal median ridge rarely developed.

Description. Valves rather thick-walled and subequal; depth equalling 12–22% of valve length. Shell slightly to moderately biconvex and acuminate-subtriangular to subcircular. Valves deepest at 30% of valve length and widest at about 55% of valve length. L/W ratio 0.81–1.14. Largest measured specimen 11.3 mm long. Larval shell subcircular, about 0.4 mm long. Postlarval ornamentation of rather coarse growth lines or rugellae (12–24 per mm), very fine concentric lines and often fine radial striations. Both larval and postlarval shell with micro-ornamentation of dense circular pits.

Dorsal pseudointerarea 4% as long and 32–52% as wide as valve, declining toward valve floor. No flexure lines observed. Pseudointerarea slightly raised above and completely separated from valve floor. Median groove moderately deep, 12–20% as wide and 4% as long as valve, with slightly convex lateral margins. Groove slightly raised above valve floor. Valve floor finely striate, generally with scattered, small, round to oblong pits in visceral area. Visceral area normally obscure, lacking median ridge. Central muscle scars longitudinally or obliquely oblong, bounding vascula media, located at 18% of valve length. Anterior lateral muscle scars subcircular to slightly elongate, small, located in scars of vascula media at 40–50% of valve length. Vascula media diverging abruptly at 10–40˚ outside visceral area and branching at about 70% of valve length. Mantle canal system baculate. Vascula lateralia diverging increasingly outward but proximal part located about one-third of valve width from valve margin.

Ventral pseudointerarea 28% as wide and 3% as long as valve, orthocline, completely separated from valve floor. Triangular propareas slightly lowered, with strong, nearly straight flexure lines. Pedicle groove narrow, shallow and subtriangular, and not or only slightly raised above valve floor. Valve floor finely striate. Visceral area generally obscure and with scattered, small, round to oblong pits. Pedicle nerve impressions subparallel posteriorly but diverging at an angle of about 35˚ anteriorly, reaching about 40% of valve length.

Remarks. Broeggeria obscura sp. nov. is highly common in several parts of the Valhallfonna Formation. It differs from the type species, Broeggeria salteri ( Holl, 1865) , in its more equidimensional and triangular outline and its striate interior, generally with an obscure visceral area. The species B. ferraria Mergl, 2002 from the Tremadocian of Bohemia also has poorly defined visceral areas (though less so than the Spitsbergen species), but differs in having an L/W ratio around 0.77, a transverse suboval outline, a distinct median ridge and gently diverging dorsal vascula media. According to its redescription by Candela & Hansen (2010) B. fimbriatus ( Hadding, 1913) from the Darriwilian and basal Sandbian in Sweden and Norway has developed marginal spines, is about 120% as long as wide, and has well-defined visceral areas. B. putilla ( Tenjakova, 1989) from the Darriwilian of Kazakhstan has visceral platforms and a subcircular outline. Broeggeria ? sp. ( Popov et al. 2008) from the Tremadocian of Iran shows too little detail for any meaningful comparison.

Occurrence. 35, 73–108 and 113 m above base of Olenidsletta Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.

Figures

FIGURE 1 Locality maps of the Svalbard Archipelago. a) Locations of sites yielding Lower Palaeozoic fossils mentioned in this paper. b) Geological map of the Basissletta plain, northeastern Ny Friesland; redrawn from Fortey & Bruton (1973). The base map is based on aerial photos made available by the Norwegian Polar Institute and on field observations made by the authors in 2008.