Ischnochiton anserinus Laghi, 1977

Ischnochiton anserinus Laghi, 1977 View in CoL

Fig. 55 View FIGURE 55

Ischnochiton ( Simplischnochiton) anserinus Laghi, 1977, p. 104 View in CoL , pl. 1, figs 10–12; Van Belle 1981, p. 20; Zanaroli 1985, p. 109, pl. 3, fig. 1.

Ischnochiton anserinus View in CoL ; Giani 1998, p. 115; Van Belle & Dell’Angelo 1998, p. 78; Dell’Angelo et al. 2001a, p. 150, figs 19, 22; Dell’Angelo et al. 2004, p. 33; Puchalski et al. 2008 (database: chiton fossil records); Dell’Angelo et al. 2012, p. 57, figs 3I, 3L; Dell’Angelo et al. 2013, p. 78.

Type material. Holotype:MPUM 18956 (1 intermediate valve). Paratypes: MPUM 18957 (1 head and 1 intermediate valves); MPUM 18958 (7 intermediate valves).

Type locality. Tagliata , Modena ( Emilia-Romagna, Italy) .

Type stage. Lower Pliocene .

Material examined. Pliocene: Italy: Tuscany: Luciana: 2 valves ( BD 441 ), Pietrafitta: 1 valve ( BD 442 , Figs 55D–E View FIGURE 55 ) ; Emilia-Romagna: Cava di Campore : 5 valves ( BD 443 , Figs 55F–H View FIGURE 55 ), Torrente Stirone: 2 valves ( BD 444 ) ; Sicily: Altavilla : 9 valves ( AG, AR, BD 445, Figs 55A–C View FIGURE 55 ). Maximum width of the valves: 4.7 mm (intermediate valves) .

Description. Head and tail valve unknown. Intermediate valve broadly rectangular (W/L = 2.66–2.75), carinate in anterior profile, highly elevated (H/W = 0.48–0.52), anterior border consisting of three segments, the two lateral ones straight and the one between the apophyses almost straight to slightly convex, side margins almost straight to slightly convex, posterior margin nearly straight, with clearly prominent apex, lateral areas moderately elevated.

LA weakly sculptured with a fine granularity giving a smooth appearance, with many concentric grooves. CA with reticulate sculpture consisting of obliquely intersecting vermicular ribs, with granules tending to separate in JA, and an almost smooth area, with some megalaesthetes arranged in parallel rows, present towards side margins. Many aesthetes irregularly distributed on tegmentum’s surface, some arranged in parallel rows present in smooth area.

Articulamentum with apophyses wide, triangular, 2 slits each side.

Remarks. The fossil record of Ischnochiton anserinus Laghi,1977 is limited to the Italian Pliocene, and is extended here to few other localities ( Cava di Campore, Torrente Stirone).

This rare species is characterized by the distinctly carinated (like the breastbone of a goose, hence the name of the species) intermediate valves, and the tegmentum sculptured with a fine granularity formed by a trellis-work of diagonal furrows, well evidenced in JA, giving a smooth appearance on LA and PA towards the side margins. Laghi established his new species on the basis of nine poor preserved and incomplete intermediate valves, and only a small fragment of a head valve, with the same sculpture of a fine granularity (practically not visible on the Laghi’s figure) giving a smooth appearance. All subsequent records of I. anserinus refer to intermediate valves.

Comparisons. This species is somewhat related to I. martinelli Dell’Angelo, Landau & Marquet, 2004; the differences are discussed under the latter species.

Distribution. Pliocene: central Mediterranean, Italy: Tuscany: Luciana, Pietrafitta; Emilia-Romagna: Cava di Campore, Torrente Stirone and Sicily: Altavilla Milicia ( Laghi 1977; Dell’Angelo et al. 2001a, 2012; this study).