Lepidochitona modesta ( Rolle, 1862 )

Lepidochitona modesta ( Rolle, 1862)

Fig. 115 View FIGURE 115

Chiton modestus Rolle, 1862, p. 215 , pl. 1, fig. 17; Van Belle 1981, p. 51; Dell’Angelo et al. 2011, p. 953; Dell’Angelo et al.

2018a, p. 11. Tonicia modesta ; de Rochebrune 1882, p. 56. Tonicella modesta View in CoL ; Dell’Angelo et al. 2018b, p. 41; Dell’Angelo et al. 2019b, p. 308, figs 3C, 6A–I; Dell’Angelo et al. 2020b,

p. 31, fig. 20; Sirenko & Dell’Angelo 2023, p. 278. Lepidochitona modesta ; Sirenko & Dell’Angelo 2023, p. 280.

Type material. Holotype NHMW 2011/0009/0001: 1 intermediate valve, width 2.4 mm ( Figs 115A–C View FIGURE 115 ).

Type locality. Gaas ( France) .

Type stage. Oligocene (Rupelian).

Material examined. Lower Oligocene (Rupelian): Gaas: type material plus 1 head valve ( NHMW 2011 /0009/0005, Fig. 115D View FIGURE 115 ), 2 intermediate valves ( BD 939 , MZB 50576 , Fig. 115H View FIGURE 115 ); Larrat: 16 intermediate valves ( AC, DA, JCV, MHNBx 2020.3.8, Figs 115E–G View FIGURE 115 ). Maximum width of the valves: 2.1 / 3.4 / -- mm .

Description. Head valve semicircular, posterior margin widely V-shaped. Intermediate valve triangular (W/L = 1.55–1.72, 1.55 in holotype), strongly beaked, semicarinate in anterior profile, highly elevated (H/W = 0.51–0.55, 0.55 in holotype), anterior margin convex, posterior margin almost straight on both sides of prominent apex, forming an angle of 101–106° (103° in holotype), lateral areas strongly delimited from central area by a diagonal fold.

Tegmentum smooth, displaying very fine microgranulation, some growth lines often present, aesthetes of same size.

Articulamentum with apophyses small and triangular, slit formula: 10 / 1 / --, with another slit just visible in intermediate valve, close to posterior margin, slit rays clearly visible.

Remarks. Lepidochitona modesta ( Rolle, 1862) is a species described on the basis of a single intermediate valve, with a characteristic shape ( Rolle, 1862: 215 “ beak -like, backwards highly elongated shape ”, translation by A. Kroh). This valve, as already noted by Rolle, could be considered as the valve ii (the first intermediate one), in several chiton species characterized by a different shape, more lengthened and beaked, and often for this reason described or illustrated separately from the other intermediate valves (e.g., Kaas et al. 2006: figs 147–150).

This species was attributed to the genus Tonicella Carpenter, 1873 by Dell’Angelo et al. (2018b), and later included by Sirenko & Dell’Angelo (2023) in the genus Lepidochitona Gray, 1821 .

The head valve preserved in NHMW ( Fig. 115D View FIGURE 115 ) has been considered by Dell’Angelo et al. (2020b) conspecific to Lepidochitona modesta , due to its tegmental surface, smooth and with arrangement of aesthetes like that of the holotype (compare Dell’Angelo et al. 2020b: figs 6C and 6G).

Comparisons. The shape of the intermediate valves of Lepidochitona modesta is very characteristic and differs from the shape of all other Lepidochitona species discussed in this study.

Distribution. Lower Oligocene: northeastern Atlantic (Rupelian): Aquitaine Basin, France: Gaas ( Rolle 1862; de Rochebrune 1882; Dell’Angelo et al. 2019 b, 2020b).