Callochiton pouweri, Dell'Angelo, Landau, Van Dingenen & Ceulemans, 2018

Callochiton pouweri View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018

Fig. 52 View FIGURE52

Callochiton pouweri View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018b, p. 32, fig. 17; Dell’Angelo et al. 2020b, p. 52, tab. 9.

Type material. Holotype MNHN.F.A67112, intermediate valve, width 4 mm ( Figs 52A–C View FIGURE52 ) . Paratypes: MNHN. F.A670113–A67114 (2 valves, Figs 52E–G View FIGURE52 ); NHMW 2017/0108/0029–0030 (2 valves, Fig. 52H View FIGURE52 ); RGM.1008411– 1008412 (2 valves) .

Type locality. Saint-Clément-de-la-Place ( France) .

Type stage. Miocene (Tortonian).

Material examined. Miocene (Tortonian): Saint-Clément-de-la-Place: type material plus 22 valves ( MNHN. F.A67115, Fig. 52D View FIGURE52 , MNHN.F.A67116, NHMW 2017 /0108/0031, RGM.1008413, BD 147 ). Maximum width of the valves:–/ 6 / 2.8 mm .

Description. Head valve unknown. Intermediate valves polygonal (W/L = 1.90–1.94), carinate in anterior profile, elevated (H/W = 0.58–0.64), anterior margin slightly convex in jugal area, side margins almost straight, inclined, posterior margin slightly concave either side of strongly protruding apex, lateral areas raised. Tail valve almost circular (W/L = 1.40), elevated, anterior margin convex, posterior margin almost semicircular, mucro subcentral or slightly anterior, antemucronal and postmucronal slopes almost straight, forming angle of ca. 40°.

Tegmentum granulose, rough. LA and PMA sculptured with fine granules, fusing into continuous radial lines, marked with few concentric growth lines toward outer margins. CA and AMA sculptured with longitudinal lines of micraesthetes, interrupted only by megalaesthetes irregularly distributed, with 6–8 conspicuous longitudinal grooves, shortening towards jugum.

Articulamentum with short, wide, regularly rounded apophyses connected at jugum by lamina, insertion plates short, teeth somewhat thickened at edges of slits, slit formula–/ 3 / 16, teeth irregular, slit rays visible, eaves very porous.

Remarks. The fossil record of Callochiton pouweri Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018 is limited to the Miocene (Tortonian) of France. The available material is not well preserved; most of the valves are small, incomplete and abraded, and head valves were not present. The presence of pigmented aesthetes (present in many species of the genus Callochiton , see Schwabe 2010; Speiser et al. 2011) has not been confirmed in C. pouweri .

Comparisons. Callochiton pouweri is similar to C. calcatus Dell’Angelo & Palazzi, 1994, from which it differs by the shape of the tail valve (mucro in anterior position and an exceptionally convex postmucronal slope in C. calcatus , see above).

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