Hanleya sancticlementensis, Dell'Angelo, Landau, Van Dingenen & Ceulemans, 2018

Hanleya sancticlementensis View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018

Fig. 46 View FIGURE 46

Hanleya sancticlementensis View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018b, p. 21, fig. 11.

Hanleya sancticlementi (sic); Dell’Angelo et al. 2020b, p. 52, tab. 9.

Type material. Holotype MNHN.F.A67080, intermediate valve, width 9 mm, Figs 46B–D View FIGURE 46 . Paratypes: MNHN. F.A67081–A67086 (6 valves), Figs 46A, 46E–H View FIGURE 46 ; NHMW 2017/0108/0012–0014 (3 valves); RGM.1008401– 1008402 (2 valves) .

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

Type stage. Miocene (Tortonian).

Material examined. Miocene (Tortonian): France: Saint-Clément-de-la-Place: type material plus 74 valves ( MNHN.F.A67087, NHMW 2017/0108/0015, RGM.1008350, RGM.1008403, BD 137 ); Sceaux d’Anjou, La Presselière: 2 valves ( BD 138 ) . Maximum width of the valves: 7 / 9 / 6 mm.

Description. Head valve subovate, posterior margin widely V-shaped. Intermediate valves polygonal (W/L = 1.77–1.84), carinate in anterior profile, moderately elevated (H/W = 0.41), posterior margin with small projecting apex, both sides slightly concave, lateral areas not raised. Tail valve elliptical, anterior margin convex, posterior margin rounded, mucro central, strongly elevated, prominent, antemucronal slope slightly convex, postmucronal slope decidedly concave directly behind mucro, straightening near posterior margin

Tegmentum surface slightly rough, without aesthetes among granules. HV, LA and PMA uniformly sculptured with scattered roundish granules, elevated, diameter 75 μm. PA and AMA with conspicuous radial depression, sculptured with elongate oval, elevated granules arranged in striae, obliquely irregularly directed, thickening and more longitudinal towards JA, where they become strongly thickened; granules irregular, oval to elongate, oblique, up to 100 μm long in PA, smaller, up to 75 μm and densely packed in JA, up to 160 μm long in AMA obliquely directed. Each granule contains one or two megalaesthetes in central position, and up to 15 or more micraesthetes irregularly disposed in CA and AMA, up to 10–12 micraesthetes arranged irregularly along margin in HV, LA and PMA; all aesthetes of same size, no aesthetes among granules.

Articulamentum solid, apophyses wide, long, connected to primordium of insertion plates in intermediate valves, insertion plates well developed both on head and tail valves, slightly pectinated on tail valve, muscle scars particularly prominent on tail valves.

Remarks. The fossil record of Hanleya sancticlementensis Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018 is limited to the Miocene (Tortonian) of the northwestern France. The material from Saint-Clément-de-la-Place consists mostly of incomplete and poorly preserved valves, especially the characters of the articulamentum are sometimes scarcely visible.

Hanleya sancticlementensis is readily distinguished from its congeners by its peculiar sculpture on PA, with irregular striae of granules obliquely directed near LA, becoming thicker and more longitudinal towards JA, with an area where the orientation of the rows is reversed, from oriented slightly to the left to oriented slightly towards the right; the rows of granules almost coalesce on JA. The triangular jugal area has a different sculpture, with rows of more appressed smaller granules. The shape and size of the granules varies on different areas of the valves, as do the number and position of aesthetes.

Comparisons. Hanleya sancticlementensis is superficially similar to H. harasewychi Sirenko, 2014 , a living species from the eastern Atlantic frontage; it differs from H. harasewychi by the shape of the intermediate valves (W/L = 1.77–1.84 vs. 2.3–2.7 in H. harasewychi ), the sculpture in PA, with granules arranged in longitudinal rows and the lack of pattern in JA of H. harasewychi .

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