Leptochiton lateropustulosus, Dell'Angelo, Landau, Van Dingenen & Ceulemans, 2018

Leptochiton lateropustulosus View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018

Fig. 26 View FIGURE 26

Leptochiton lateropustulosus View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018b, p. 16, fig. 8; Dell’Angelo et al. 2020b, p. 52, tab. 9.

Type material. Holotype MNHN.F.A67071, intermediate valve, width 6.3 mm ( Figs 26B–D View FIGURE 26 ) . Paratypes: MNHN. F.A67072–A67074 (head, intermediate and tail valves, Figs 26A, 26G–H View FIGURE 26 ); NHMW 2017/0108/0008–0010 (head, intermediate and tail valves, respectively); RGM.1008365, intermediate valve ( Figs 26E–F View FIGURE 26 ) .

Type locality. Saint-Clément-de-la-Place, Anjou , France .

Type stage. Miocene (Tortonian).

Material examined. Upper Miocene (Tortonian): Saint-Clément-de-la-Place: type material plus 36 valves ( MNHN.F.A67075, NHMW 2017 /0108/0011, RGM.1008366, RGM.1008398, BD 135 ). Maximum width of the valves: 6.3 / 7 / 4.7 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, notched in middle, slope straight. Intermediate valve broadly rectangular, width more than three times the length (W/L = 3.32–3.40), rounded to subcarinate in anterior profile, moderately elevated (H/W = 0.22–0.39), anterior margin slightly convex, side margins rounded, posterior margin straight, apex not developed, lateral areas slightly raised. Tail valve almost semicircular, width ca. two times the length (W/L = 1.96), anterior margin convex, mucro in anterior position, antemucronal slope slightly convex, postmucronal slope concave, more pronounced concavity just behind mucro, antemucronal area short, less than one–third of length of postmucronal area.

Tegmentum rough. HV, LA and PMA sculptured with radial granular striae intersected by concentric growth lines, with some elevated pustules irregularly distributed on striae (HV ca. 76, LA ca. 12, PMA ca. 65), concentric growth lines continuing across central area, where they weaken, becoming inconspicuous. CA and AMA sculptured with longitudinal granular striae, weakening anteriorly, not reaching anterior margin, subobsolete in jugal area, which appears smooth without magnification. Each granule with a central megalaesthete and 5–6 micraesthetes irregularly disposed.

Articulamentum without insertion laminae, apophyses well developed, bluntly triangular with a rounded margin.

Remarks. The record of Leptochiton lateropustulosus Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018 is to date limited to the original material from the Miocene (Tortonian) of France ( Dell’Angelo et al. 2018b).

The intermediate valves are highly variable in shape (H/W = 0.22–0.39, 0.34 in holotype) and most markedly in the sculpture of PA and JA, where many granular longitudinal striae do not reach the anterior margin.

Leptochiton lateropustulosus View in CoL is closest to Leptochiton eckelsheimensis ( Gürs, 1992) from the lower Oligocene (Rupelian) of Steigerberg ( Germany). Dell’Angelo et al. (2018b) were unsuccessful in locating the type material, which is not in the SMF (R. Janssen, pers. comm.), nor in Mainz, Naturhistorisches Museum (K. Grimm, pers. comm.), nor in Kiel, Geologisches Landesamt, nor in the Landesamt für Natur und Umwelt (E. Schwabe, pers. comm.). Unfortunately the description given by Gürs (1992) is incomplete, as important diagnostic information is missing (e.g., the profile of intermediate valves, the slopes of tail valves and the scale of the figures is not indicated). Moreover, the two intermediate and the two tail valves figured seem to differ in shape (compare Gürs 1992, figs 1b–1c and 1d–1e). The intermediate valve in fig. 1b could be interpreted as a valve ii (often a bit different from other intermediate valves iii–vii) and both of the valves have the longitudinal granular striae on pleural areas short, whereas Gürs (1992) noted in his description that in some other intermediate valves the sculpture may reach the anterior valve margin. Despite the great similarity between the material from Saint-Clément-de-la-Place and the illustrations given by Gürs (1992), the unavailability of the type material for comparison and the conspicuous difference in stratigraphic age convinced Dell’Angelo et al. (2018b) to describe the French material as a new species.

Comparisons. The characteristics of the sculpture of Leptochiton lateropustulosus View in CoL agree with the belonging of the species to the Leptochiton cancellatus View in CoL group, see Tab. 2. The sculptural character of irregularly distributed pustules along the radial granular striae on HV, LA and PMA seen in Leptochiton lateropustulosus View in CoL is an uncommon character in European Cenozoic chitons.

Distribution. Upper Miocene: northeastern Atlantic (Tortonian): Ligerian Basin, France: Saint-Clément-de-la-Place ( Dell’Angelo et al. 2018b).