Rhyssoplax etrusca

Rhyssoplax etrusca (Dell’Angelo & Forli, 1995)

Fig. 90 View FIGURE 90

Chiton ( Rhyssoplax) etruscus Dell’Angelo & Forli, 1995a, p. 233, figs 2–5, 9, 19.

Chiton etruscus ; Giani 1998, p. 115; Dell’Angelo et al. 2001a, p. 152, fig. 26; Chirli 2004, p. 13, pl. 5, fig. 3–10; Schwabe 2005, p. 95; Puchalski et al. 2008 (database: chiton fossil records); Dell’Angelo & Schwabe 2010, p. 14; Dell’Angelo et al. 2012, p. 61, 89; Dell’Angelo et al. 2013, p. 89; Dell’Angelo et al. 2018b, p. 38; Forli & Guerrini 2022, p. 173, fig. 11.18 (13–14).

Type material. Holotype MZB 11623 (intermediate valve) ( Dell’Angelo et al. 2001a). Paratypes: MZB 12692 (head valve), MZB 12695 (tail valve), MCZR (3 valves), Civico Museo Archeologico e di Scienze Naturali di Alba, n° reg. G-1125 (4 valves), and private collections (12 valves): BD FX18A/C12 (5 valves, Figs 90D–F View FIGURE 90 ), MF (5 valves), LD (1 valve), VB F1001a (1 valve) .

Type locality. Riparbella ( Tuscany, Italy) .

Type stage. Lower Pleistocene .

Material examined. Pliocene Spain : El Papiol: 63 valves ( BD 731 ) . Italy: Piedmont: Vintebbio: 135 valves ( BD 732 ) ; Tuscany: Cetona “Palazzo Tosoni”: 6 valves ( BD 733 ) ; Colle Val d’Elsa : 42 valves ( BD 734 ) ; Orciano Pisano : 33 valves ( BD 735 ) ; Pietrafitta : 200 valves ( BD 736 , Figs 90G–H View FIGURE 90 ) ; Pietrafitta Melograni : 89 valves ( BD 737 ) ; Poggio alla Fame : 38 valves ( BD 738 , Figs 90J–L View FIGURE 90 ) . Pleistocene : Italy: Tuscany: Fauglia: 68 valves ( BD 739 ) , Riparbella : type material plus 336 valves ( BD 740 , Figs 90A–C, 90I View FIGURE 90 , MF) ; Calabria: Le Castella: 11 valves ( BD 741 ) . Maximum width of the valves: 2.3 / 2.5 / 3.2 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, front slope straight. Intermediate valves broadly rectangular (W/L = 1.96–2.19), elevated (H/W = 0.50–0.65), rounded to semicarinate in anterior profile, anterior margin straight to slightly convex, side margins truncated, posterior margin straight but for the small, sharp-pointed apex, lateral areas raised, clearly separated from CA. Tail valve semicircular (W/L = 1.57–1.65), anterior margin slightly convex, mucro in slightly anterior position, antemucronal slope straight, postmucronal slope slightly concave.

HV, LA and PMA smooth, concentric growth lines vaguely indicated. CA and AMA sculptured with 5-8 longitudinal folds at both sides of smooth jugum, all folds reach up to anterior margin, with exception of most central one (or last two) on each side. Aesthetes very dense, each megalaesthete accompanied by many micraesthetes.

Articulamentum with apophyses wide, subtrapezoidal, connected across narrow, shallow sinus by a short, dentate jugal plate, slit formula 8–10 / 1 / 11–14, slits inequidistant, slit rays hardly or not indicated, teeth short, finely pectinate, eaves narrow, minutely porous.

Remarks. Rhyssoplax etrusca (Dell’Angelo & Forli, 1995) is only known from Pliocene and Pleistocene of Tuscany, very frequent at Riparbella, where is the most abundant chiton.

Comparisons. Rhyssoplax etrusca is very similar to R. phaseolina ( Monterosato, 1879) , from which it differs mainly by the more elevated intermediate valves, H/W = 0.50–0.65 vs. 0.40–0.50 in R. phaseolina, LA raised, clearly separated from CA, and almost all the longitudinal folds on CA reaching the anterior margin.

Distribution. Pliocene: western Mediterranean, Spain: El Papiol (this study); central Mediterranean, Italy: Cetona, Colle Val d’Elsa, Orciano Pisano, Pietrafitta,Pietrafitta Melograni, Poggio alla Fame, Vintebbio ( Dell’Angelo et al. 2001a; Chirli 2004; this study). Pleistocene: central Mediterranean, Italy: Fauglia, Le Castella, Riparbella ( Dell’Angelo & Forli, 1995a; this study).