Cyrtonotreta spinosa, 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 : 51-53

Cyrtonotreta spinosa sp. nov.

Pl. 12, Figs. 5–16; Pl. 13, Figs. 1–3

1975 Conotreta sp. ―Krause & Rowell, pp. 40–41, Pl. 4, Figs. 25–30; Pl. 11, Fig. 3 .

Derivation of name. Latin ‘ spinosus ’, spinose; refers to the spiny pustules on the rugellae.

Holotype. UKMIP 79807 in the collections at the Paleontological Institute at the University of Kansas, dorsal valve; Krause & Rowell (1975) Pl. 4, Figs. 29–30; basal part of Antelope Valley Formation (Dapingian), Meiklejohn Peak , Nevada. New figures were unfortunately unattainable for this monograph.

Material from Spitsbergen. Fragments of 28 dorsal and 26 ventral valves from samples F3797, JH-45, JH-52 and JH-136. Figured specimens are TSGF 16803–16808, TSGF 16995 and TSGF 16997.

Diagnosis. Cyrtonotreta with dense rugellae covered with minute spiny pustules; poorly developed median division of ventral pseudointerarea; dorsal median ridge or low septum lacking rod and with apex generally near front; poorly developed median buttress.

Description of Spitsbergen material. Shell large, thick-walled, with subcircular to transversely oval outline and slightly convex posterior margin. Larval shell subcircular, about 0.21 mm long, with dense micro-pitting. Pits deep, subcircular, 0.8–2.6 µm in diameter. Postlarval ornamentation consisting of dense, low, uneven rugellae, about 8–14 per 0.2 mm. Numerous spiny pustules lying close to surface on rugellae, normally oriented toward umbo or perpendicular to valve surface. Pustules 0.01–0.03 mm long, generally unordered but occasionally arranged in irregular, radiating rows. Pustules lacking on rugellae within ventral pseudointerarea and occasionally also in other parts of shell.

Dorsal valve slightly convex to slightly concave and often lacking sulcus. Pseudointerarea low, concave, orthocline or anacline. Median groove broad, shallow, and ill-defined, with straight or slightly concave anterior margin. Interior with angular thickened marginal rim. Cardinal-muscle scars obscure. Median buttress poorly developed. Thin, subtriangular median ridge or low septum with apex normally in anterior half and front at marginal rim.

Ventral valve moderately conical. Posterior and anterior slopes nearly straight. Lateral slopes gently convex. Pseudointerarea high, procline, more than half as wide as valve. Interridge or intertrough poorly developed. Foramen small, circular, located within posterior part of larval shell. Larval shell moderately convex. Internal pedicle tube short and broad. Apical process a broad low thickening of the anterior valve floor near the apex.

Remarks. The Spitsbergen specimens are found to be conspecific with the specimens identified as Conotreta sp. by Krause & Rowell (1975). The species is similar to the other known species of Cyrtonotreta but exhibits two unique features: (1) a median septum lacking a septal rod and (2) spiny pustules.

Plate 12

Cyrtonotreta profilbekkiensis sp. nov.

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

1–3. TSGF17000 , holotype, ventral valve exterior, oblique anterolateral view, and larval shell .

4. TSGF16998 , paratype, ventral valve interior .

Cyrtonotreta spinosa sp. nov.

Valhallfonna Formation, Olenidsletta Member.

5–6. TSGF16995, exterior of dorsal valve fragment and detail of ornamentation. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH-136.

7. TSGF16804, oblique posterolateral view of damaged dorsal valve interior. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45.

8. TSGF16805, interior dorsal valve fragment showing angular rim. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH- 45.

9–10. TSGF16806, oblique lateral and ventral view of interior of dorsal valve fragment. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45.

11–15. TSGF16807, oblique anterolateral and oblique posterolateral views, ventral view, larval shell, and detail of larval micro-ornamentation of ventral valve. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45.

16. TSGF16997, detail of postlarval ornamentation of ventral valve. 97 m above base. Coll. J. Hansen, 28.07.2008, sample JH- 136.

Occurrence. 84, 90, 94 and 97 m above base of Olenidsletta Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen. Basal part of Antelope Valley Formation (Dapingian), Nevada.

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.