Acanthochitona oblonga ( Leloup, 1981 )

Acanthochitona oblonga ( Leloup, 1981) View in CoL

Fig. 139 View FIGURE 139

Acanthochiton oblongus Leloup, 1981, p. 1 View in CoL , figs 1a–1d, pl. 1; Kaas 1985a, p. 596, figs 39–43.

Acanthochitona oblonga View in CoL ; Gaglini 1985, p. xviii, pl. 1, fig. 6; Gaglini 1989: 9; Dell’Angelo & Smriglio 1999, p. 201, pl. 67, figs K–L; Dell’Angelo et al. 2001a, p. 153; Dell’Angelo et al. 2004, p. 40; Bonfitto et al. 2011, p. 174, figs 2A–B, 4C, 6C; Dell’Angelo et al. 2013, p. 97, pl. 10, figs N–Q; Schmidt-Petersen et al. 2015, p. 17, figs 5–6, tab. 1; Dell’Angelo et al. 2016, p. 89, pl. 6, figs 3–4; Dell’Angelo et al. 2018b, p. 43; Dell’Angelo et al. 2020b, p. 40, 53, tab. 9; Dulai & Katona 2024, p. 44, figs 39–42.

Acanthochitona crinita View in CoL f. oblonga View in CoL ; Dell’Angelo & Forli 1995a, p. 237, fig. 6.

Type material. Holotype MU, one specimen, 14 mm long.

Type locality. Salina Bay ( Malta), “under rocks at 3 meters depth” .

Material examined. Upper Miocene: Italy: Montegibbio: 3 valves ( BD 1109, MZB 32114, Figs 139A–B View FIGURE 139 ), Rio di Bocca d’Asino: 1 valve ( BD 1110). Lower Pliocene: Italy: Liguria: Bussana: 7 valves ( BD 1111, MZB 45769–45770, Figs 139C–D View FIGURE 139 ), Rio Sant’ Antonino: 1 valve ( MP). Pleistocene: Italy: Tuscany: Riparbella: 8 valves ( BD 1112). Recent: S. Foca ( Italy): valves ( BD 3811, Figs 139E–H View FIGURE 139 ). Maximum width of the intermediate valves: 4 mm.

Description. Head valve semicircular, posterior margin straight, slope slightly convex. Intermediate valves broadly rectangular (WT/LT = 1.73), semicarinate in anterior profile, moderately elevated (H/W = 0.42), anterior margin straight between apophyses, posterior margin almost straight on both sides of pronounced apex, jugal area longitudinally striated, raised. Tail valve broadly circular (WT/LT = 1.29), jugal area longitudinally striated, raised, mucro well evident, subcentral, antemucronal slope almost straight, postmucronal slope slightly concave.

Whole tegmentum (except jugal area) sculptured with widely spread, oval, strongly elongated granules, irregularly arranged in radial striae, JA longitudinally striated; granules of variable size, 3-5 times as long as wide, maximum size 275 μm, with a single posteriorly located megalaesthete generally surrounded by 6 to 9 micraesthetes, irregularly grouped mainly in middle part of granules.

Articulamentum well developed, apophyses quadrangular and strongly protruding, delimiting a wide jugal sinus, slit formula - / 1 / -.

Remarks. This species, described by Leloup based on 4 specimens collected at Salina Bay ( Malta), is characterized by the very extended sharp granules of the tegmentum. After the original description, it has been reported from other Mediterranean localities ( Dell’Angelo & Smriglio 1999); large series from the Apulian Adriatic coast demonstrate greater variability of granules with respect to Leloup’s original description.

Acanthochitona oblonga ( Leloup, 1981) is so similar to A. crinita ( Pennant, 1777) that subsequent authors (e.g., Kaas 1985a; Dell’Angelo & Smriglio 1999) consider them as conspecific, until Bonfitto et al. (2011) demonstrated its specific validity based on morphological and molecular argunments.

In paleontological legacy the species is known as intermediate valves from the Middle Miocene of Paratethys, upper Miocene of N. Italy, lower Pliocene of Liguria and the Pleistocene of Riparbella.

Comparisons. See Tab. 22 for a comparison with the Acanthochitona spp. considered in the present study.

Distribution: Middle Miocene: Central Paratethys (Langhian-Serravallian): Hungary: Várpalota ( Dulai & Katona 2024). Upper Miocene: Proto-Mediterranean Sea (Tortonian): Po Basin, N. Italy: Montegibbio, Rio di Bocca d’Asino ( Dell’Angelo et al. 2016). Lower Pliocene: central Mediterranean, Italy: Liguria: Bussana, Rio Sant’Antonino ( Dell’Angelo et al. 2013). Pleistocene: central Mediterranean, Italy: Riparbella ( Dell’Angelo & Forli 1995a). Recent: Southern Mediterranean Sea in scattered Italian localities, Malta, Cyprus, Tunisia ( Dell’Angelo & Smriglio 1999; Bonfitto et al. 2011).