Lepidochitona tenuissima (Sandberger, 1859)

Lepidochitona tenuissima (Sandberger, 1859)

Fig. 129 View FIGURE 129

Chiton tenuissimus Sandberger, 1859 , pl. 14, figs 3, 3a, 3b; Sandberger 1861, p. 185; Boettger 1869, p. 10, pl. lb, figs l2a–12b; Boettger 1870, p. 40, pl. 8b, figs 12a–12b; Wenz 1932, p. 14.

Lepidopleurus tenuissimus ; de Rochebrune 1882, p. 57.

Tonicella tenuissima View in CoL ; Janssen 1978, p. 223, pl. 16, figs 31–35; Van Belle 1981, p. 76; Gürs 1983, p. 57, pl. 1, figs 1, 2a–2c, 3a–3b; Gürs 1995, p. 31; Dell’Angelo et al. 2011, p. 954; Dell’Angelo et al. 2018b, p. 41; Cherns & Schwabe 2019, p. 10; Dell’Angelo et al. 2020b, p. 35, fig. 22; Sirenko & Dell’Angelo 2023, p. 278, fig. 6. Lepidochitona tenuissima ; Sirenko & Dell’Angelo 2023, p. 280.

Type material. The holotype (an intermediate valve) was lost due to war circumstances ( Janssen 1978).

Type locality. Gienberg ( Germany) .

Type stage. Oligocene (Rupelian).

Material examined. Lower Oligocene (Rupelian): Germany: Glimmerode: 7 valves ( BD 954, Figs 129A–B, 129H View FIGURE 129 ), Gienberg: 2 valves ( BD 955, Figs 129C–D, 129G View FIGURE 129 ). Upper Oligocene (Chattian): France: Abesse: 5 valves ( BD 956, DA, MZB 50577, Figs 129E–F View FIGURE 129 ); Ruisseau de l’église: 1 intermediate valve ( JFL). Maximum width of the valves: 2.3 / 4 / 3.7 mm-

Description. Head valve semicircular. Intermediate valves broadly rectangular (W/L = 2.41–3.10), semicarinate in anterior profile, moderately elevated (H/W = 0.39–0.40), anterior margin almost straight to slightly convex, side margins fairly straight, posterior margin almost straight, apex not very prominent, lateral area slightly raised, separated from central one by a distinct ridge. Tail valve semicircular, small, lightly projecting, subcentral mucro, antemucronal area separated from postmucronal one by a low ridge and a depression in front of that ridge.

Tegmentum smooth and glossy, with prominent growth lines, aesthetes of same size.

Articulamentum with apophyses wide, but not projecting far, insertion plates short, teeth irregular, slit formula 9 /1 / 7, with a second slit very close to the posterior margin in intermediate valves, slit rays visible.

Remarks. This species was originally described by Sandberger (1859) based on a single intermediate valve from the lower Oligocene (Rupelian) of Germany. Unfortunately, the type material was lost during the Second World War. Later, Janssen (1978) described and illustrated valves from the type locality, as well as valves from late Oligocene localities in Germany, under the name Tonicella tenuissima , and attributed head and tail valves to this species.

This species was placed in Tonicella Carpenter, 1873 , by Janssen (1978), and later included by Sirenko & Dell’Angelo (2023) in the genus Lepidochitona Gray, 1821 , widespread in the Tethys Ocean since the Eocene.

Dell’Angelo et al. (2020b) discussed a few intermediate and a single tail valve, from the Oligocene (Chattian) of the Aquitaine Basin, that agree with the features of L. tenuissima .

The shape W/L of the intermediate valves of Lepidochitona tenuissima is variable, the valves are elongate, ca. 3 times as wide as long, W/L = 2.92–3.10, vs. 2.41 measured on the valve of L. tenuissima , figured by Janssen (1978: pl. 16, fig. 32); two valves from Waldbockelheim ( Germany: BD collection) with a W/L ratio of 2.5 and 2.92, respectively, has been attributed to L. tenuissima .

Comparisons. Lepidochitona tenuissima (Sandberger, 1859) differs from L. lira ( Cherns & Schwabe, 2019) mainly by the smooth surface (vs. lateral areas rugose in L. lira ), the posterior margin tapering to a pointed apex (vs. almost straight with apex not evident in L. lira ) and the presence of a rib separating lateral and pleural areas (not present in L. lira ). See Tab. 18–21 for comparison with the other Lepidochitona spp . considered in the present study.

Distribution. Lower -upper Oligocene: North Europe, Germany: Böseberg, Gienberg, Glimmerode, Welschberg, Würzmühle (Sandberger 1859; Janssen 1978; Gürs 1983; this study); Upper Oligocene: northeastern Atlantic (Chattian): Aquitaine Basin, France: Abesse, Ruisseau de l’église ( Dell’Angelo et al. 2020b).