Lepidochitona nuda

Lepidochitona nuda ( Dell’Angelo, Lesport, Cluzaud & Sosso, 2020)

Fig. 116 View FIGURE 116

Tonicella nuda View in CoL Dell’Angelo, Lesport, Cluzaud & Sosso, 2020b, p. 36, fig. 21; Sirenko & Dell’Angelo 2023, p. 278. Lepidochitona nuda ; Sirenko & Dell’Angelo 2023, p. 280.

Type material. Holotype: MHNBx 2020.3.9, tail valve, width 2.3 mm ( Figs 116F–H View FIGURE 116 ). Paratypes: MHNBx 2020.1.3, head valve, width 3 mm ( Figs 116A–B View FIGURE 116 ); MHNBx 2020.1.4, intermediate valve, width 3.8 mm ( Figs 116C–E View FIGURE 116 ). Type locality. Gaas , Larrat ( France). Type stage. Oligocene ( Rupelian ). Material examined. Oligocene ( Rupelian ): Gaas : type material plus 9 valves ( BD 940 ); Lagouarde: 3 valves ( DA); Larrat: 214 valves ( AC, DA, JCV). Maximum width of the valves: 3 / 4.4 / 2.7 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, front slope straight, slight presence of radial folds. Intermediate valves broadly rectangular, width more than twice the length (W/L = 2.05–2.50), semicarinate in anterior profile, moderately to highly elevated (H/W = 0.41–0.51), anterior margin slightly convex, almost straight in jugum, lateral margins rounded, posterior margin concave at both sides of prominent apex, lateral areas delimited from central area by diagonal fold, in some valves scarcely visible, second weaker diagonal fold present on posterior margin. Tail valve semicircular, width about twice the length (W/L = 1.93–2.10), anterior margin slightly convex, straight or slightly concave in jugal portion, mucro subcentral, antemucronal slope almost straight, postmucronal slope straight or slightly convex.

Tegmentum smooth, glossy, with several inconspicuous growth lines, one or two more evident near anterior margin on head valve, aesthetes of same size.

Articulamentum with apophyses triangular, trapezoidal in tail valve, weakly projecting, slit formula 8–9 / 1 / 8, insertion plates short, teeth irregular, slit rays clearly visible in head and intermediate valves, scarcely visible in tail valves.

Remarks. This species was initially attributed to the genus Tonicella Carpenter, 1873 by Dell’Angelo et al. (2020b), and later included by Sirenko & Dell’Angelo (2023) in the genus Lepidochitona Gray, 1821 .

There is a certain variability in the shape of intermediate valves (the width/length ratio ranges from 2.05 to 2.50, and the anterior profile, with H/W = 0.41–0.51) and tail valves (the width/length ratio ranges from 1.93 to 2.36). The head valves have a sculpture with slight presence of radial folds.

Comparisons. Lepidochitona nuda ( Dell’Angelo, Lesport, Cluzaud & Sosso, 2020) is similar to L. tenuissima (Sandberger, 1859) (see below), from which it differs mainly by the smooth surface with the presence of poorly or hardly visible growth lines (very prominent along the entire surface of the valves in L. tenuissima ), and by the shape of intermediate valves (W/L = 2.05–2.50 vs. 2.41–2.96 in L. tenuissima ; H/W = 0.41–0.51 vs. 0.39–0.42 in L. tenuissima ).

Distribution. Lower Oligocene: northeastern Atlantic (Rupelian): Aquitaine Basin, France: Gaas ( Dell’Angelo et al. 2020b).