Conchoprimitia, Opik, 1935

Salas, María José & Vaccari, N. Emilio, 2012, New insights into the early diversification of the Ostracoda: Tremadocian ostracods from the Cordillera Oriental, Argentina, Acta Palaeontologica Polonica 57 (1), pp. 175-190 : 183-184

Conchoprimitia ? iglesiasi sp. nov.

Fig. 7 .

Etymology: This species is named for Saturnino Iglesias, an Argentinian geologist who collected the specimens of N. coquena and this species.

Holotype: JUY−P 043 left valve ( Fig. 7C ).

Type locality: Road N ° 9 (km 1,651.5 km), between Salta and Jujuy cities, northwest Argentina .

Type horizon: Floresta Formation, 24°29‘21.91“S 65°17‘53.40”O. Paltodus deltifer Biozone, Tr 2.

Diagnosis.—Subcircular and postplete outline. Valves with a tiny and rounded preadductorial node and a short and poorly defined sulcus.

Description.—Valves subcircular and postplete in outline. Average L:H = 1.56. Dorsal margin straight and long, only slightly shorter than maximum length of valves. The maximum length is at the mid−height of the valves. Cardinal angles obtuse, with the posterior one bigger than the anterior one. Lateral and ventral margins evenly rounded. The valves bear a tiny, and rounded preadductorial node. The node is in the anterior half of the valve near the dorsal margin. Immediately behind, there is a short, straight, and poorly defined sulcus, perpendicular to the dorsal margin. Marginal surface rather steep in the anterior half, where the valves are wider. In juveniles the marginal surface is steep in the posterior half too. Lateral surface smooth.

Material.— Twenty specimens collected by Saturnino Iglesias, including the figured material JUY−P 041–044. Specimens we have examined range from 0.56 mm to 1.48 mm in length. Discussion.—The taxonomic position of this species is un−

clear. It is similar in lateral outline to the species of Conchoprimitia , however, other features differ rather considerably. The new species has a small, and rounded node, and an indistinct sulcus. The described material resembles several Early and Middle Ordovician species of Conchoprimitia , and even some Circulinidae like Vogdesella Baker, 1924 . The Argentinian species is similar to Conchoprimitia socialis ( Brögger, 1882) from the Middle Ordovician of the Oslo region in the subcircular outline of the valves, and in the presence of a node and a sulcus in the antero dorsal part of the carapace ( Henningsmoen 1954: pl. 2: 1–6). However, the new species is smaller (L = 1.48 mm in C.? iglesiasi sp. nov., L = 4.45 mm in C. socialis ), the valves are postplete, the nodes are more rounded and poorly defined, and the steepest area is anterodorsally whereas in the Baltic species is postero−ventrally. Conchoprimitia sp. ( Tinn and Meidla 2004: fig. 5A–D) from the Dapingian of Baltic has a short and poorly defined sulcus, however, it is more elongated and has very well defined retention marks, unknown in the new species. Conchoprimitia distincta ( Sarv, 1959) (in Schallreuter 1989: fig. 5.1–2) from the Darriwilian of Baltic has a circular and postplete outline, and a very indistinct sulcus, however, it has an important swell in the posterodorsal half of the valves, and the carapace is punctuated. Conchoprimitia ? polonica Olempska, 1994 ( Olempska 1994: pl. 47: 14–16), from the Darriwilian of Poland, has a postplete outline, a short and indistinct sulcus, and a weakly developed preadductorial node as Conchoprimitia ? iglesiasi sp. nov. In the Argentinian species, however, L is longer, the cardinal corners are more defined and they are not rounded, the anterior margin is not so sharp, the valves are less

http://dx.doi.org/10.4202/app.2009.1110

convex, and the preadductorial node is small and rounded. The new species also resembles Vogdesella aequae Olempska, 1994 ( Olempska 1994: pl. 44: 10–12) from the Darriwilian of Poland, however, the Argentinian form is bigger, N1 is small and sharp, and N2 is not present or is very indistinct.

Stratigraphic and geographic distribution.—Known only from the type locality.

Figures

Fig. 7. Late Tremadocian conchoprimitid ostracod Conchoprimitia? iglesiasi sp. nov. Iglesias collection, from the Floresta Formation, Abra de Santa Laura section of the Cordillera Oriental Argentina. A. JUY−P 041, internal mould of right valve, lateral view. B. JUY−P 042, internal mould of left valve, lateral view. C. Holotype JUY−P 043, left valve in lateral view. D. JUY−P 044, left valve in lateral view. Scale bars 200 µm.