Rhaetian (Late Triassic) ostracods (Crustacea, Ostracoda) from the offshore prolongation of the North Dobrogean Orogen into the Romanian Black Sea shelf Author Forel, Marie-Béatrice 063C1F7E-6D26-48F9-A8B1-2AFA496B5FB8 Muséum national d’histoire naturelle, CR 2 P, MNHN-CNRS-SU, 8 rue Buffon (CP 38), 75005 Paris, France. marie-beatrice.forel@mnhn.fr;eugen.gradinaru@g.unibuc.ro Author Grădinaru, Eugen DE8A275A-486D-478F-9333-0FE0F7D30A78 Department of Geology, Faculty of Geology and Geophysics, University of Bucharest, Bd. Bălcescu Nicolae 1, RO- 010041 Bucharest, Romania. marie-beatrice.forel@mnhn.fr;eugen.gradinaru@g.unibuc.ro text European Journal of Taxonomy 2020 2020-12-08 727 1 83 journal article 9348 10.5852/ejt.2020.727.1183 aebff7a2-6d62-4b2c-850e-90c203eb690b 4316845 85AF63D9-5E9E-4CE0-AEC6-6F7CC8C4D375 Isobythocypris atalantella Forel sp. nov. urn:lsid:zoobank.org:act: E98F39D0-EF52-4BEC-A66B-439D4AD1D442 Fig. 9 B–I Diagnosis A new species of Isobythocypris with long and slightly arched dorsal margin, relatively large posterior border. Etymology From Άταλάντη / Átalántê, the only Augonaut woman. Material examined Holotype ROMANIA • 1 complete carapace; Black Sea , Romanian Continental Shelf , borehole 817LV, sample CM31B; Rhaetian, Upper Triassic ; MNHN.F. F63246 . Paratype ROMANIA • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic ; MNHN.F. F63247 . Other material ROMANIA • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic ; MNHN.F. F63248 • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic ; MNHN.F. F63249 • 1 complete carapace; same collection data as for holotype; Rhaetian, Upper Triassic ; MNHN.F. F63251 • 1 complete carapace; same locality as for preceding but sample CM31C; Rhaetian, Upper Triassic ; MNHN.F. F63250 • 9 complete carapaces; same locality as for preceding but samples CM31A, CM31B and CM31C; Rhaetian, Upper Triassic ; MNHN.F. F63354 . Dimensions See Fig. 3F . Description Carapace of medium size, ovoid in lateral view, with H max around mid-L, L max slightly below mid-H, W max slightly posterior to mid-L; LV larger than RV, overlapping along dorsal margin and oral concavity, with interruption at AVB and PVB. Dorsal margin long and slightly convex, lacking angulations at LV, with weak angulations at RV resulting from tight folds of overlapping LV; antero-dorsal slope gentle in large specimens (± 10°), slightly steeper in smaller ones (± 20°); DB straight, somewhat sloping posteriorly (±25–35°); postero-dorsal slope short, steep, often poorly differentiated; anterior margin large, only slightly tapered ventrally, with poorly expressed bairdiid morphology and maximum of curvature at mid-H; ventral margin long and sinuous, with median oral concavity expressed on both valves, only slightly more in RV; AVB only slightly raised, PVB horizontal; posterior end narrowly rounded. Inner structures not observed. Surface smooth. Occurrence Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper). Remarks Isobythocypris atalantella sp. nov. is relatively close to the species of Bythocypris illustrated in Bolz (1971b) . Of them, Bythocypris sp. A is only shown as inner views ( Bolz 1971b : pl. 8, figs 118–119), which makes a comparison difficult. However, Isobythocypris atalantella sp. nov. differs from Bythocypris sp. A and Bythocypris sp. B from the Rhaetian of the Northern Calcareous Alps ( Bolz 1971b ) by its narrower and uniformly convex posterior margin, which is close to vertical in both species of Bythocypris . Isobythocypris atalantella sp. nov. also differs from Bythocypris ubiquefrequens Bolz, 1971 from the Rhaetian of the Northern Calcareous Alps ( Bolz 1971b ) in having a longer and less curved dorsal margin, a less marked bairdiid anterior margin and a larger posterior maximum of curvature. Isobythocypris atalantella sp. nov. is morphologically close to Isobythocypris ? sp. in Dreyer 1967 from the Early Domerian, Early Jurassic, of Germany ( Dreyer 1967 ) but the PB of Isobythocypris ? sp. is nearly vertical, with the maximum of curvature narrower and located more ventrally. It also differs from Isobythocypris elongata ( Blake, 1876 ) from the Early Jurassic of Yorkshire ( Blake 1876 ) by having a larger and not angulate posterior border. Isobythocypris atalantella sp. nov. also differs from Bythocypris faba Knitter, 1983 from the Toarcian, Early Jurassic, of Southern Germany ( Knitter 1983 ) by its more homogeneous convex dorsal margin, anterior maximum of convexity located higher and posterior border located lower and less bairdiid. The H/L scatter plot of all measurable specimens of Isobythocypris atalantella sp. nov. ( Fig. 3F ) documents the occurrence of at least five ontogenetic stages, from A-4 to adult. The holotype ( Fig. 9 B–C) is the largest known adult. Conversely, the paratype ( Fig. 9D ) may correspond to an A-1 stage. The ontogeny of Isobythocypris atalantella sp. nov. is marked by the overall elongation of the carapace, narrowing of the PB and accentuation of the median oral concavity on both valves.