Scrobicula gracilis, Casier & Olempska, 2008

Casier, Jean-Georges & Olempska, Ewa, 2008, Early Frasnian ostracods from the Arche quarry (Dinant Synclinorium, Belgium) and the Palmatolepis punctata Isotopic Event, Acta Palaeontologica Polonica 53 (4), pp. 635-646 : 638

Scrobicula gracilis sp. nov.

Fig. 3H–J .

2006 Paraparchitidae ? sp. indet.; Głuchowski et al. 2006: fig. 2E.

Etymology: From the Latin gracilis —slim, thin. Referring to the fineness of the ornamentation.

Holotype: IRScNB n° b5062. Carapace. AR−06−20. Fig. 3H 1 , H 2. L = 0.57 mm; H = 0.36 mm; W = 0.30 mm.

Type locality: Access path to the Arche quarry.

Type horizon: Chalon Member of the Moulin Liénaux Formation, Early Frasnian, Devonian.

Diagnosis.—Small leperditoid carapace with a slim depression and with a finely wrinkled ornamentation.

Material.—Six carapaces and valves (samples AR−06−20 and AR−06−23). The description is also based on several specimens from the Nismes section (study in progress) and from the Frasnes railway section ( Casier and Olempska 2008).

Description.—Small preplete carapace with a slightly convex dorsal border and a delicately curved or nearly straight ventral margin. The anterior and the posterior margins are regularly rounded, but the curvature of the last one is more accentuated. The greater length is at mid−height, and the greater height is at the anterior third of the carapace. Both cardinal angles (about 150°) located in the anterior and posterior sixth of the length. The left valve is larger than the right valve, and in right lateral view projects all along the free and dorsal margins. The carapace is biconvex in dorsal view, moderately wide, with the greatest width located just posterior of mid−length. The straight hinge line is in a slim depression. The finely wrinkled ornamentation and the muscle scar are only faintly visible. The inner wrinkles are concentric around a circular muscle scar; the exterior wrinkles follow the contour of the free margin and terminate against the dorsal border. The ornamentation is comparable to finger−print ornamentation observed in many entomozoid ostracods.

Remarks.—The species is easily distinguishable from the majority of species belonging to the genus Scrobicula by its elliptical contour in dorsal view. Where the finely wrinkled ornamentation is preserved, S. gracilis differs from all the species of genus Scrobicula . In Belgium the species is also present in the Pont d’Avignon Member, in the Sourd d’Ave Member and in the Chalon Member exposed in the Nismes section (study in progress). Paraparchites ? sp. A figured by Casier and Olempska (2008) from the Frasnes railway section belongs also to the new species. In that section, S. gracilis is present in the Ermitage Member and also in the Bieumont and Boussu−en−Fagne Members of the Middle Frasnian Grand Breux Formation. The Paraparchitidae ? sp. indet. recorded by Głuchowski et al. (2006) from the middle Wietrznia Beds ( Pa. transitans Conodont Zone ) of the Wietrznia quarry in the Holy Cross Mountains, Poland, belongs to S. gracilis .

Figures

Fig. 3. Early Frasnian ostracods from the access path to the Arche quarry, Dinant Synclinorium, Belgium. A, B. Refrathella incompta Becker, 1971. A. Carapace in right (A) and dorsal (A) views. Sample AR−06−28. IRScNB n° b5055. B. Left valve. Sample AR−06−26. IRScNB n° b5056. C–E. Uchtovia 1 2 materni Becker, 1971. C. Heteromorph carapace in left lateral view. Sample AR−06−26. IRScNB n° b5057. D. Heteromorph carapace in dorsal view. Sample AR−06−28. IRScNB n° b5058. E. Tecnomorph carapace in dorsal view. Sample AR−06−28. IRScNB n° b5059. F, G. Hypotetragona tremula Becker, 1971. F. Heteromorph carapace in left lateral view. Sample AR−06−23. IRScNB n° b5060. G. Tecnomorph carapace in dorsal view. Sample AR−06−28. IRScNB n° b5061. H–J. Scobicula gracilis sp. nov. H. Holotype. Carapace in left lateral (H) and dorsal (H) views. Sample AR−06−20. IRScNB n° b5062. 1 2 I. Carapace in left lateral view. Sample NI−07−136 from the Sourd d’Ave Member in the Nismes section. IRScNB n° b5063. J. Carapace in left lateral view. Sample NI−07−12 from the Chalon Member in the Nismes section. IRScNB n° b5064.K. Cavellina? sp. A. Carapace in left (K) and dorsal (K) views. Sam1 2 ple AR−06−26. IRScNB n° b5065. L–N. Plagionephrodes laqueus praelaqueus ssp. nov. L. Holotype. Carapace in right lateral (L) and dorsal (L) views. 1 2 Sample AR−06−27. IRScNB n° b5066. M. Internal view of right valve. Sample AR−06−17. IRScNB n° b5068. N. Internal view of left valve. Sample AR−06−18. IRScNB n° b5069. O. Plagionephrodes ineptus Becker, 1971. Carapace in right (O) and dorsal (O) views. Sample AR−06−28. IRScNB n° 1 2 b5070. Scale bar 200 µm.

Fig. 1. Locality map of the Arche quarry, the Lion quarry and the Frasnes railway section; the access path to the Arche quarry indicated by arrow.

Fig. 2. Lithologic sections of the Chalon Member and of the extreme base of the Arche Member exposed on the north−eastern side and on the south−eastern side of the access path to the Arche quarry.