Leptochiton scabridus ( Jeffreys, 1880 )

Leptochiton scabridus ( Jeffreys, 1880) View in CoL

Fig. 22 View FIGURE 22

Chiton scabridus Jeffreys, 1880, p. 33 ; Pilsbry 1894, p. 94; Gaglini 1985, pl. 12, figs 1–2.

Lepidopleurus cancellatus View in CoL [non Leptochiton cancellatus ( Sowerby, 1840) View in CoL ]; Laghi 1977, pl. 1, figs 1–3; Dell’Angelo & Palazzi, 1989 p. 67 ( fide Dell’Angelo & Palazzi 1989).

Lepidopleurus scabridus View in CoL ; Sykes 1894, p. 35, pl. 3, figs 4, 7; Thiele 1909, p. 9, pl. 1, figs 5–10;

Lepidopleurus ( Leptochiton) scabridus View in CoL ; Dell’Angelo & Palazzi 1989, p. 65, pls 16–17; Giovine & Dell’Angelo 1993, p. 160, pl. 1, figs 1–3; Dell’Angelo & Smriglio 1999, p. 63, pls 16–17, figs 25–26; Garilli et al. 2005, p. 130, pl. 2, figs 1–4.

Leptochiton ( L.) scabridus View in CoL ; Kaas & Van Belle 1985a, p. 49, fig. 19, map 11; Dell’Angelo & Palazzi 1986, p. 11, figs 11–14, 19–22, 32–34, 45–48, 54–55, 60; Cesari 1987, p. 7, pl. 2, figs. 1–8; pl. 3, figs. 1–10; pl. 4, figs. 1–6; pl. 5, figs 1–11; pl. 11, figs. 4–6; Kaas & Van Belle 1988, p. 12, map 1.

Leptochiton scabridus View in CoL ; Dell’Angelo et al. 2013, p. 71, pl. 2, figs E–G; Dell’Angelo et al. 2015a, p. 226, pl. 3, figs 7–11; Dell’Angelo et al. 2018b, p. 52; Dell’Angelo et al. 2022, p. 6, figs 3.10–3.15.

Type material. Syntypes: Goodrington , Torbay: 1 specimen ( USNM 177391 About USNM ); Jersey: 15 specimens ( USNM 177392 About USNM ) ( fide Warén 1980) .

Type locality. Goodrington , Torbay, England and Jersey ( Channel Islands) .

Material examined. Upper Miocene: Italy: Montegibbio: 1 valve ( MZB 32013), Rio di Bocca d’Asino: 3 valves ( BD 397, MZB 32012). Lower Pliocene: Italy: Liguria: Genova Sestri: 1 valve ( MZB 45702, Fig. 22D View FIGURE 22 ).

Pliocene: Portogallo: 14 valves ( BD 238, GeoFCUL VFX.03.333, GeoFCUL VFX.03.350, RGM.1363999– 1364000, MNHN.F. A81982 View Materials , Figs 22G–L View FIGURE 22 ). Italy: Tuscany: Poggio alla Fame: 2 valves ( BD 258). Pleistocene: Italy: Calabria: Pecoraro: 2 valves ( BD 398, Figs 22E–F View FIGURE 22 ). Greece: Kyllini: 2 valves ( BD 399, DGUP, Figs 22A–C View FIGURE 22 ). Maximum width of the valves: 1.4 / 3.7 / 2 mm.

Description. Valves small, fragile. Head valve semicircular, posterior margin widely V-shaped. Intermediate valves broadly rectangular, length more or less three times the width (W/L = 2.88–3.30), rounded in anterior profile, moderately elevated (H/W = 0.25–0.32), anterior margin straight, side margins rounded, posterior margin straight, apex not indicated, lateral areas hardly raised but clearly indicated. Tail valve semicircular (W/L = 1.77–1.90), front margin straight to slightly convex, mucro about central, somewhat swollen, antemucronal slope convex, postmucronal slope concave.

Tegmentum rough, space between striae of granules large, some growth lines, more evident in LA. HV, LA and PMA sculptured with irregular subquadrangular/subrhomboidal granules well separated from each other, arranged in radiating series (HV 36–48, LA 7–8, PMA 30–36). CA and AMA sculptured with irregular subquadrangular/ subrhomboidal granules well separated from each other, arranged in longitudinal series (CA 24–30), tending to become slightly converging near outer sides and looking like square mesh, granules extended with 2–3 longitudinal varices that become unified or merge together along external margin of valve. Each granule with a central megalaesthete and some micraesthetes irregularly disposed.

Articulamentum lacking insertion laminae, apophyses small, sharply triangular, widely separated.

Remarks. Leptochiton scabridus ( Jeffreys, 1880) was described but not figured by Jeffreys and is quoted by Pilsbry (1894) only in Appendix II (“ Insufficiently described Chitons, and species of unknown generic position ”), which, however, reports the original description. It was first figured by Sykes (1894), while Thiele (1909) described the radula and the girdle on a topotypic specimen from Jersey. The species was described with a distribution limited to a small zone of the British Channel along the English and French coasts, and subsequently it was rarely found in other areas of the Mediterranean, initially confused with L. cancellatus ( Dell’Angelo & Palazzi 1989; Dell’Angelo & Smriglio 1999).

Possibly because of uncorrect attributions to the close species Leptochiton cancellatus (see Dell’Angelo & Palazzi, 1989: 61), historical records are doubtful and require confirmation.The fossil record of Leptochiton scabridus is limited thus far to the upper Miocene of Italy ( Dell’Angelo et al. 2015a), the Pliocene of Italy ( Dell’Angelo et al. 2013) and Portugal ( Dell’Angelo et al. 2022), and the Pleistocene of Italy (this study) and Greece ( Garilli et al. 2005).

Comparisons. The species that have the greatest similarities with Leptochiton scabridus are those that share the sculpture of the tegmentum formed by striae of granules well separated from each other ( L. serenae Dell’Angelo, Piccioli Resta & Bonfitto, 2007 and L. josei Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013). These species differ from each other for a series of characteristics relating to the shape and sculpture of the valves, well highlighted in Tab. 2.

Distribution. Upper Miocene: Proto-Mediterranean Sea (Tortonian): Po Basin, N Italy: Montegibbio, Rio di Bocca d’Asino ( Dell’Angelo & Palazzi 1989; Dell’Angelo et al. 2015a). Lower Pliocene: central Mediterranean, Italy: Liguria: Sestri Ponente ( Dell’Angelo et al. 2013). Pliocene: northeastern Atlantic, Mondego Basin, Portugal: Vale de Freixo ( Dell’Angelo et al. 2022); central Mediterranean, Italy: «La Tagliata», Modena ( Laghi 1977, as L. cancellatus ; Dell’Angelo & Palazzi 1989), Poggio alla Fame (this study). Pleistocene: central Mediterranean, S. Italy: Pecoraro (this study), Greece: Kyllini ( Garilli et al. 2005). Recent: Atlantic Ocean: S.W. U.K. and the British Channell ( Light & Baxter 1990), France: Bretagne ( Van Belle 1972), northern Spain ( Urgorri et al. 2017), Portugal ( Consolado Macedo et al. 1999), Canary Islands ( Hernández & Rolán 2011), Cape Verde Islands ( Kaas 1991) and Angola ( Dell’Angelo & Smriglio 1999). Mediterranean Sea: Italy: Tuscan Archipelago ( Dell’Angelo & Palazzi, 1986), Taranto Gulf and Otranto coast ( Dell’Angelo & Palazzi 1986; Baschieri 1994), and many other localities ( Dell’Angelo & Palazzi 1986; Dell’Angelo & Smriglio 1999); Greece and Aegean Sea Islands ( Strack 1988; Koukouras & Karachle 2005); Malta ( Mifsud et al. 1990); Turkey ( Ozturk et al. 2014).