Ischnochiton martinelli

Ischnochiton martinelli Dell’Angelo, Landau & Marquet, 2004

Fig. 59 View FIGURE 59

Ischnochiton martinelli Dell’Angelo, Landau & Marquet, 2004, p. 33, pl. 4, fig. 8, pl. 5, figs 1–4, 6–8, pl. 6, figs 1–8, pl. 7, fig. 1; Schwabe 2005, p. 98; Puchalski et al. 2008 (database: chiton fossil records); Dell’Angelo et al. 2012, p. 58, figs 3M–O; Dell’Angelo et al. 2013, p. 78, pl. 4, fig. A.

Type material. Holotype: MZB 25051 (intermediate valve, Figs 59C–D View FIGURE 59 ). Paratypes: MZB 25052 (3 valves); MME (3 valves, Figs 59A–B View FIGURE 59 ); IRSN IST 6450 View Materials (3 valves); BD 4567 (3 valves); RM (3 valves) .

Type locality. Estepona , Velerín Carretera ( Málaga, Spain) .

Type stage. Early Piacenzian (Pliocene).

Material examined. Lower Pliocene: Italy: Liguria: Caranchi: 2 valves ( BD 456 , MZB 45716 ) , Rio Sant’Antonino : 1 valve ( MP) . Pliocene : Spain: Estepona : type material plus 26 valves ( BD 457 ) . Italy: Emilia-Romagna: Cava di Campore : 8 valves ( BD 458 ) , Lugagnano Val d’Arda : 1 valve ( BD 459 ) ; Tuscany: Orciano Pisano: 1 valve ( BD 460 ) ; Sicily: Altavilla : 24 valves ( AG, AR, BD 461, Figs 59E–F View FIGURE 59 ). Pleistocene : Italy: Calabria: Archi S. Francesco: 35 valves ( BD 462 , Figs 59G–L View FIGURE 59 ), Bovetto: 1 valve ( BD 463 ) , Terreti , Ponte Cellantoni: 4 valves ( BD 464 ) ; Sicily: Salice : 3 valves ( BD 465 ) . Maximum width of the valves: 4.8 / 6.5 / 4.1 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, notched in middle, front slope straight to slightly concave. Intermediate valves broadly rectangular (W/L = 2.57–3.01), carinate in anterior profile, moderately to highly elevated (H/W = 0.36–0.54), anterior margin consisting of three segments, two lateral segments concave, and the one between the apophyses convex, side margins slightly convex, posterior margin nearly straight, apex little evident, lateral areas moderately elevated. Tail valve semicircular (W/L = 2.10), with anterior margin similar to that of intermediate valves, mucro subcentral, antemucronal slope slightly convex, postmucronal slope slightly concave behind mucro

HV, LA and PMA sculptured with radial nodulose riblets (HV 26–30, LA 4–5), becoming indistinct toward apex, with squarish nodules formed by many concentric grooves crossing riblets. CA and AMA sculptured with a reticulate sculpture consisting of obliquely intersecting vermicular ribs, with granules tending to separate in JA, and tending to form about ten real longitudinal striae in pleural area, often somewhat eroded, and an almost smooth area, with some megalaesthetes arranged in parallel rows, present towards side margins. Tegmentum fully covered by aesthetes, both on nodular elevations (without a clearly recognizable structure of megalaesthetes and micraesthetes) and between them.

Articulamentum with apophyses wide, triangular in intermediate valves, trapezoidal in tail valve, separated by narrow jugal sinus, slit formula 9–11 / 1–2 / 11, slits inequidistant.

Remarks. The fossil record of Ischnochiton martinelli Dell’Angelo, Landau & Marquet, 2004, so far limited to the Pliocene of Estepona ( Spain) and Italy ( Liguria and Sicily) is extended here to other Pliocene and Pleistocene localities from Italy. The valves from the Italian Pleistocene well agree with the same material from the Pliocene localities.

The number of slits in the intermediate valves is more difficult to evaluate, also because the characteristics of the articulamentum are not always clearly visible. Some valves show a second slit ray near the posterior margin, but without evidence of a real slit, which is instead clearly noticeable in the valve illustrated ( Fig. 54I View FIGURE 54 ) from Archi S. Francesco.

Comparisons. Ischnochiton martinelli is similar to I. anserinus Laghi, 1977 , only known from intermediate valves, with which it shares the carinate anterior profile of intermediate valves, and from which it differs mainly by the sculpture of LA, with a fine granularity, giving a smooth appearance in I. anserinus , vs. radial nodulose riblets with squarish nodules in I. martinelli .

Distribution. Pliocene: western Mediterranean, Estepona Basin, Spain: Estepona (Dell’Angelo et al. 2004); central Mediterranean, Italy:Altavilla, Caranchi, Rio S. Antonino ( Dell’Angelo et al. 2012, 2013), Cava di Campore, Lugagnano Val d’Arda, Orciano Pisano (this study). Pleistocene: central Mediterranean, S. Italy:Archi S. Francesco, Bovetto, Salice, Terreti (this study).