Parachiton palmorum, Dell'Angelo, Lesport, Cluzaud & Sosso, 2018

Parachiton palmorum View in CoL Dell’Angelo, Lesport, Cluzaud & Sosso, 2018

Fig. 39 View FIGURE 39

Parachiton palmorum View in CoL Dell’Angelo, Lesport, Cluzaud & Sosso, 2018a, p. 19, fig. 4G–L; Dell’Angelo et al. 2020b, p. 52, tab. 9.

Type material. Holotype: MHNBx 2017.9.1, tail valve, width 3.2 mm ( Figs 39A–C View FIGURE 39 ). Paratype: MZB 32134, tail valve, width 3 mm ( Fig. 39D View FIGURE 39 ).

Type locality. Carrière Vives ( France) .

Type stage. Miocene (Burdigalian).

Material examined. Lower Miocene: France (Burdigalian): type material .

Description. Head and intermediate valves unknown. Tail valve semicircular, wider than long (W/L estimated 1.66), depressed, rounded in anterior profile, mucro posterior, located at about 2/10th of valve’s length towards posterior margin, antemucronal slope slightly convex, postmucronal slope straight, but for a little excavation directly behind mucro.

Tegmentum finely granulose.AMA sculptured with oval fine granules arranged in 50 enough regular longitudinal series, diverging anteriorly on sides. PMA sculptured with roundish granules arranged in ca 70 radial series, crossed by two concentric growth lines.

Articulamentum weakly developed, apophyses small.

Remarks. Parachiton palmorum Dell’Angelo, Lesport, Cluzaud & Sosso, 2018 is only known from the original description, based on two tail valves from the lower Miocene of Carrière Vives ( France).

Comparisons. This species resembles Parachiton africanus ( Nierstrasz, 1906) , from which differs by the shape of the tail valve (much wider than long in P. palmorum , W/L estimated ca. 1.66 vs. 1.14–1.28 in P. africanus ), the position of the mucro (located more posteriorly in P. africanus ), and the sculpture of the longitudinal rows of granules, well evidenced and not coalescing in P. palmorum , fairly smoothly coalescing in P. africanus .

Parachiton palmorum differs from P. statianus Dell’Angelo, Giuntelli, Sosso & Zunino, 2015 by the position of the mucro (located more posteriorly in P. statianus ), the sculpture of the longitudinal rows of granules (well evidenced and not coalescing in P. palmorum , fairly smoothly coalescing in P. statianus ), and the number of longitudinal (50 vs. 90–95) and radial (70 vs.> 100) rows of granules.

Distribution. Lower Miocene: northeastern Atlantic (Burdigalian): Aquitaine Basin, France: Carrière Vives ( Dell’Angelo et al. 2018a).