Rhyssoplax sulcomarginata

Rhyssoplax sulcomarginata ( Dell’Angelo, Giuntelli, Sosso & Zunino, 2016)

Fig. 96 View FIGURE 96

Chiton sp. B View in CoL ; Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013, p. 89, pl. 7, figs K–N.

Chiton sulcomarginatus Dell’Angelo, Giuntelli, Sosso & Zunino, 2016, p. 82, pl. 3, figs 5–12.

Rhyssoplax sulcomarginatus ; Dell’Angelo et al. 2018a, p. 31; Dell’Angelo et al. 2020b, p. 52, tab. 9.

Rhyssoplax sulcomarginata ; Dell’Angelo et al. 2021b, p. 422, figs 114–121.

Type material. Holotype: MZB 32084 (tail valve, width 2.5 mm, Figs 96F–H View FIGURE 96 ). Paratypes: MZB 32082 (intermediate valve from Albugnano, Fig. 96C View FIGURE 96 ); MZB 32083 (tail valve from Albugnano); MZB 32085 (head valve from Montegibbio, Figs 96A–B View FIGURE 96 ).

Type locality. Rio di Bocca d’Asino ( Piedmont, Italy) .

Type stage. Miocene (Tortonian).

Material examined. Middle Miocene: Italy: Albugnano: type material plus 1 valve ( PG). Upper Miocene : Italy: Rio di Bocca d’Asino: type material plus 2 valves ( BD 831 ); Montegibbio: 1 valve ( BD 832 ). Lower Pliocene : Italy: Liguria: Borzoli : 4 valves ( BD 833 , MZB 45748 , Fig. 96E View FIGURE 96 ), Bussana: 2 valves ( BD 834 ), Genova Sestri: 2 valves ( BD 835 , MZB 45749 , Fig. 96D View FIGURE 96 ). Maximum width of the valves: 4.6 / 3.6 / 3.9 mm .

Description. Head valve semicircular. Intermediate valve broadly rectangular, anterior margin straight between apophyses, posterior margin little concave at both sides of well pronounced apex, lateral areas raised. Tail valve semicircular (W/L = 1.84–1.88), little elevated, small anterior mucro, antemucronal slope straight, postmucronal slope concave.

HV, LA and PMA smooth, except some light radial ribs restricted to area near margins. CA and AMA smooth, except for 3–4 small ribs each side obliquely directed, near margins. Aesthetes very dense, each megalaesthete accompanied by many micraesthetes.

Articulamentum scarcely visible, slit formula: 8–9 / 1 / 10.

Remarks. The fossil record of Rhyssoplax sulcomarginata ( Dell’Angelo, Giuntelli, Sosso & Zunino, 2016) is limited to the Miocene and Pliocene of Italy; the material examined is represented by small and badly preserved valves. The description is therefore less complete than that of the other Rhyssoplax spp .

Comparisons. The main differential character is the presence of 3–4 small ribs obliquely directed, in PA and AMA areas near the side margin, and of some light ribs only in a small part near the margins of HV, LA and PMA.

Distribution. Middle Miocene: Proto-Mediterranean Sea (Langhian): Po Basin: Albugnano ( Dell’Angelo et al. 2016). Upper Miocene: Proto-Mediterranean Sea (Tortonian): Po Basin, N Italy: Rio di Bocca d’Asino, Montegibbio ( Dell’Angelo et al. 2016). Lower Pliocene: central Mediterranean, N Italy, Liguria: Borzoli, Bussana, Genova Sestri ( Dell’Angelo et al. 2013).