Ischnochiton ulivii

Ischnochiton ulivii View in CoL Dell’Angelo & Forli, 1996

Fig. 62 View FIGURE 62

Ischnochiton ulivii View in CoL Dell’Angelo & Forli, 1996, p. 46, figs 16–26; Giani 1998, p. 115; Van Belle & Dell’Angelo 1998, p. 78; Dell’Angelo et al. 2001a, p. 150, fig. 21; Chirli 2004, p. 7, pl. 2, figs 10–15; Dell’Angelo et al. 2004, p. 33, pl. 4, figs 6–7; Schwabe 2005, p. 104; Puchalski et al. 2008 (database: chiton fossil records); Dell’Angelo et al. 2013, p. 78.

non Ischnochiton ulivii View in CoL ; Sosso & Dell’Angelo 2010, p. 14 (= I. ligusticus View in CoL Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013, fide Dell’Angelo et al. 2013: 78).

Type material. Holotype: MZB 11654, 1 intermediate valve ( Dell’Angelo et al. 2001a). Paratypes: MZB 12698– 12699 (1 head and 1 tail valves); DSTUT B-P.I.07.1 (3 valves: 2 from Pietrafitta “Sbarra”, 1 tail from Pietrafitta Melograni); private collections: BD F55D/2 (3 valves from Pietrafitta Melograni), MF (3 valves from Pietrafitta Melograni), EU (3 valves from Pietrafitta Melograni), VB F1002a (3 valves from Pietrafitta Melograni).

Type locality. Pietrafitta “Sbarra” ( Tuscany, Italy) .

Type stage. Pliocene.

Material examined. Pliocene: Spain: Estepona : 1 valve ( BD 520 , Figs 62K–L View FIGURE 62 ) . Italy: Tuscany: Aiano: 1 valve ( BD 521 ), Bibbiano: 8 valves ( BD 522 ), Colle Val d’Elsa : 2 valves ( BD 523 ), Orciano Pisano: 1 valve ( BD 524 ), Pietrafitta: type material plus 54 valves ( BD 525 , Figs 62A–G View FIGURE 62 ), Poggio alla Fame: 26 valves ( BD 526 ). Pleistocene : Italy: Tuscany: Fauglia : 8 valves ( BD 527 , Figs 62H–J View FIGURE 62 ), Riparbella: 2 valves ( BD 528 ). Maximum width of the valves: 2.7 / 3.3 / 2.8 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, front slope straight. Intermediate valves broadly rectangular, moderately elevated (H/W = 0.32–0.45), rounded in anterior profile, anterior margin straight, side margins slightly rounded, posterior margin almost straight, apex not evident or hardly pronounced in some valves, lateral area not evident, practically indistinguishable from central area. Tail valve semicircular, anterior margin straight, mucro hardly pronounced and visible, subcentral or slightly anterior, antemucronal slope almost straight or slightly convex, postmucronal slope almost straight or slightly concave.

Tegmentum evenly granulose. HV, LA and PMA sculptured with minute tubercles irregularly arranged (more or less quincuncially), sometimes arranged in concentric arcs in LA, especially towards side margin, giving the impression of more or less continuous cords. CA and AMA sculptured with small but neat irregularly arranged depressions, giving a pitted appearance.

Articulamentum with rather pronounced apophyses, insertion lamina divided into short and well-marked teeth, of fairly regular length, slit formula 10–11 / 1–2 / 10–12.

Remarks. The fossil record of Ischnochiton ulivii Dell’Angelo & Forli, 1996 is limited to the Pliocene of Spain (Estepona) and Italy (random records in Tuscany) and the Pleistocene of Italy (Riparbella). Ischnochiton ulivii is characterized by the small dimensions, the minute tubercles more or less quincuncially arranged on the entire valve’s surface, and a decidedly pitted sculpture in CA and AMA.

The tegmentum sculpture of Ischnochiton ulivii is very characteristic, and at first look resembles the four Recent species known from the Cape Verde Archipelago characterized by an evenly granulose tegmentum [ I. cessaci (de Rochebrune, 1881) also from Mauritania, Sénégal, Angola, and Canary Islands, I. goreensis Thiele, 1909 also from Sénégal, I. paessleri Thiele, 1909 , and I. nicklesi Kaas & Van Belle, 1990 also from Dakar], from which it differs by its smaller dimensions, the different slit formula, the shape of the tail valve, and mainly a much coarser sculpture.

Comparisons. The present species is closest to Ischnochiton ligusticus Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013 (see above).

Distribution. Pliocene: western Mediterranean, Estepona Basin, Spain: Estepona (Dell’Angelo et al. 2004); central Mediterranean, Italy: Tuscany: Aiano, Bibbiano, Colle Val d’Elsa, Orciano Pisano, Pietrafitta, Poggio alla Fame ( Dell’Angelo & Forli 1996; Dell’Angelo et al. 2001a; Chirli 2004; this study). Pleistocene: central Mediterranean, Italy: Fauglia, Riparbella ( Dell’Angelo et al. 2001a; this study).