Cyrtonotreta profilbekkiensis, 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 : 49-51

Cyrtonotreta profilbekkiensis sp. nov.

Pl. 11, Figs. 14–15; Pl. 12, Figs. 1–4

Derivation of name. Refers to both the locality and the member from which the specimens were collected.

Holotype. Pl. 12, Figs. 1–3 ; TSGF17000 , ventral valve; 21 m above base of Profilbekken Member, Valhallfonna Formation, sample JH-23; Profilbekken meltwater stream at Basissletta, Ny Friesland, Spitsbergen.

Material. Fragments of 4 dorsal valves and 15 ventral valves from samples JH-23 and JH-184. The paratypes are TSGF16998 , TSGF17001 and TSGF17002 .

Diagnosis. Cyrtonotreta with very wide and strongly developed apical process and procline to catacline ventral pseudointerarea about half as wide as valve; interridge generally absent; dorsal sulcus absent.

Description. Shell transversely oval to subcircular with gently convex posterior margin. Pseudointerarea about half as wide as maximum valve width. Micro-ornamentation on larval shell consisting of dense, shallow and unevenly rounded pits ranging in size from 1 to 3 µm. Postlarval shell with growth lines.

Dorsal valve slightly convex and without sulcus. Umbo minute. Pseudointerarea low, gently concave, anacline. Median groove wide, very shallow and poorly defined. Dorsal median septum low and broad proximally, becoming thin and moderately high distally. Median buttress wide. Cardinal muscle scars moderately impressed.

Ventral valve low conical with concave lateral and anterior slopes. Larval shell moderately convex. Pseudointerarea poorly defined, procline to catacline, generally without interridge. Foramen damaged in all specimens but enclosed by larval shell at apex of valve. Mantle canal with moderately impressed, posterolaterally directed vascula lateralia. Apical process strongly developed, forming a platform on lateral and anterior sides of short internal pedicle tube.

Remarks. The type species, Cyrtonotreta depressa ( Cooper, 1956) from the Darriwilian of Alabama, USA, differs from C. profilbekkiensis sp. nov. by having a markedly narrower apical process and a generally catacline to steeply apsacline ventral pseudointerarea. C. osekensis Mergl, 2002 from the Darriwilian of Bohemia differs by having a distinct interridge, a weak dorsal sulcus, and an apical process with a shallow pit. C. robusta Percival in Percival et al., 2009 from the Darriwilian of New Zealand has a nearly straight and wide posterior margin, a strongly defined ventral pseudointerarea, and strongly impressed muscle scars in both valves. C? striata Holmer, 1989 from the Darriwilian of Sweden differs from the new species in having a markedly narrower pseudointerarea, a rather narrow apical process, and a moderately developed interridge. C. vestrogothica Holmer, 1989 from the upper Darriwilian of Sweden differs in having a distinct upper septal rod and an apical process only about half as wide. Cyrtonotreta sp. a in Holmer (1989) from the Darriwilian to Sandbian of Sweden differs in having a narrow apical process and a much narrower internal pedicle tube. Cyrtonotreta sp. b in Holmer (1989) from the Darriwilian of Sweden differs in having a narrow pseudointerarea and a distinct dorsal septal rod. Cyrtonotreta sp. in Popov (2000a) from the Ashgillian of Kazakhstan differs in having an intertrough and a straight or convex anterior slope. Cyrtonotreta sp. ( Nikitina et al. 2006) from the Darriwilian of Kazakhstan differs in having a narrow interridge and a very short dorsal pseudointerarea.

Occurrence. 21 and 26 m above base of Profilbekken Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.

Plate 11

Conotreta ? devota Krause & Rowell, 1975

Valhallfonna Formation.

1–2. TSGF16923, dorsal valve interior and oblique anterolateral view thereof. Profilbekken Member, 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184.

3–4. TSGF16849, dorsal valve interior and oblique lateral view thereof. Olenidsletta Member, 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52.

5–6. TSGF16918, dorsal valve interior and oblique anterolateral view thereof. Olenidsletta Member, 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136.

7–9. TSGF16922, ventral valve exterior, oblique anterolateral view, and larval shell. Profilbekken Member, 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184.

10–11. TSGF16920, ventral valve exterior and oblique anterolateral view thereof. Profilbekken Member, 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184.

12–13. TSGF16921, ventral valve interior and oblique anterolateral view thereof. Profilbekken Member, 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184.

Cyrtonotreta profilbekkiensis sp. nov.

Valhallfonna Formation, Profilbekken Member, 21 m above base. Coll. J. Hansen, 19.07.2008, sample JH-23.

14. TSGF17001 , paratype, fragment of dorsal valve with pseudointerarea .

15. TSGF17002 , paratype, oblique anterolateral view of fragment of dorsal valve with part of median septum .

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.

FIGURE 2 Stratigraphical ranges and diversity of brachiopod species at Basissletta, Spitsbergen, and relative sea levels and percentages of linguliform brachiopods in the total brachiopod fauna. White shading in the last graph indicates stratigraphical intervals without brachiopods. Thicknesses of units are according to Fortey & Bruton (1973). Lithological log and sea level curve are from Hansen & Holmer (2010).

FIGURE 3 Rose histograms for the umbonal orientation of the large brachiopod Ectenoglossa? oviforma sp. nov. found in the Olenidsletta Member, Valhallfonna Formation. a) Histogram of 58 specimens from 88 m above the base of the member. b) Histogram of 13 specimens from 94 m above the base of the member.