Evlanella peranensis Maillet

Maillet, Sebastien, Milhau, Bruno, Vreulx, Michel & Posada, Luis-Carlos Sánchez De, 2016, Givetian ostracods of the Candás Formation (Asturias, North-western Spain): taxonomy, stratigraphy, palaeoecology, relationship to global events and palaeogeographical implications, Zootaxa 4068 (1), pp. 1-78 : 25

Evlanella peranensis Maillet n. sp.

( Fig. 4 ; Pl. I: Figs. 22–25, Pl. II: Figs. 1 & 2 )

aff. 1990 Sulcella nov. sp. A; Casier in Casier & Préat: 86–87, pl. 1, figs. 21–23. 2013 Evlanella ? sp. P1; Maillet: 78, pl. IX, figs. 12–13.

Derivation of name. “ peranensis ”: Latinized from Peran, type-locality of the species.

Diagnosis. Large Evlanella with a marked and anterior adductorial sulcus, an inflated carapace with, especially posteriorly, flattened margins, a reticulated ornamentation with longitudinally stretched polygonal reticles, a small knob posteriorly to the sulcus and no spiral ridge.

Holotype. A left valve of tecnomorph (C. O.F.L.S. 800), 950 µm in length and 500 µm in height (Pl. I: Fig. 23).

Paratypes. A left valve of heteromorph (C. O.F.L.S. 1124), 1090 µm in length and 630 µm in height (Pl. I: Fig. 24) and a left valve of juvenile (C. O.F.L.S. 1125), 460 µm in length and 235 µm in height (Pl. I: Fig. 25).

Material. 48 specimens (6 C, 14 V, 28 F).

Type locality and horizon. Upper Middle Givetian (Candás Fm, Member C, around the middle/upper P. varcus Zones boundary), Peran-Perlora section (Asturias, Spain).

Description. Large elongated carapace, sub-rectangular in lateral view. Almost equivalve carapace, with RV very slightly larger than LV. Hmax at 1/3 posterior; Lmax median; Wmax median in tecnomorphs and more posterior in heteromorphs. Dorsal margin almost straight, very slightly concave in its medium part. Stragulum not observed. Ventral margin almost straight, more convex at its extremities. Dorsal and ventral margins almost parallel. Anterior margin well-rounded, more arched in its dorsal part. Posterior margin regularly convex and forming an angle of about 110° with the dorsal margin. Posterior part slightly higher than the anterior one. Very marked adductorial sulcus at 2/5 anterior and extending from mid-height towards the dorsal margin. Carapace flattened along the free margins, more especially along the posterior one. Otherwise, inflated carapace around the sulcus. Small knob posteriorly to the sulcus. Surface reticulated, with longitudinally stretched polygonal reticles. In ventral view, fine marginal ridge along the line of closure of the valves. In lateral view, juvenile carapaces show a well developed posterior flattening and an adductorial sulcus more median than in adults.

Discussion. By their large size, the general outline of the carapace and characteristics of the postero-dorsal angle, these specimens are comparable to other Evlanella species. The absence of a spiral ridge and the marked adductorial sulcus particularly remind of E. mitis Adamczak, 1968 from the Eifelian of Poland, from which specimens from Peran-Perlora differ by ornamentation and marginal flattening of the carapace. The morphology of described specimens also resembles Sulcella nov. sp. A in Casier & Préat (1990), by the large size of the carapace, its general outline and the marked adductorial sulcus. However, ornamentation is quite different, with absence of longitudinal ridges in E. peranensis and presence of a knob posteriorly to the adductorial sulcus.

Occurrence. Middle Givetian (Candás Fm, mb C), Asturias (Peran-Perlora section).

Figures

FIGURE 1. Location maps of the studied area. A. Devonian deposits cropping out in the Cantabrian Zone (adapted from García-Alcalde et al. 2012); B. Simplified geological map of the Luanco-Candás area showing the Naranco, the Candás and the Piñeres Fms (modified from García-López et al. 2002), with location of the Peran-Perlora and Carranques sections; C. Detailed location map of the Peran-Perlora section (adapted from García-López et al. 2002); D. Detailed location map of the Carranques section (adapted from Fernández et al. 1996).

FIGURE 2. Simplified stratigraphical column of the Candás Formation, standard conodont zonation and chronostratigraphy (according to García-Alcalde et al. 1979; García-López 1986 and García-López et al. 2002).

FIGURE 4. Height / length diagram for Evlanella peranensis Maillet n. sp .. The trendline equation (y) is indicated.