Craspedochiton minutulus Bałuk, 1971

Craspedochiton minutulus Bałuk, 1971

Fig. 147 View FIGURE 147

Craspedochiton minutulus Bałuk, 1971, p. 465 , pl. 6, figs 9–13; Laghi 1977, p. 112, pl. 4, figs 13–16; Van Belle 1981, p. 50; Bałuk 1984, p. 293, pl. 10, figs 1–5, pl. 11, figs 1–7; Zanaroli 1985, p. 117, pl. 1, figs 8–9; Macioszczyk 1988, p. 55, pl. 4, figs 1–3; Studencka & Studencki 1988, p. 43, 44; Dell’Angelo et al. 1999, p. 285; Puchalski et al. 2008 (database: chiton fossil records); Studencka & Dulai 2010, p. 271; Dell’Angelo et al. 2011, p. 949; Ruman & Hudácková 2015 (cf.), p. 165, figs 4.3–4.4; Dell’Angelo et al. 2016, p. 91, pl. 6, figs 20–21, pl. 7, figs 1–8; Dell’Angelo et al. 2020b, p. 44, tab. 9.

Type material. Holotype in Bałuk collection, reg. No. BkK-A57, an intermediate valve ( Bałuk 1971: pl. 6, fig. 9).

Type locality. Korytnica , southern slopes of the Holy Cross Mts. ( Poland) .

Type stage. Middle Miocene.

Material examined. Miocene (Tortonian): Italy: Montegibbio : 28 valves ( BD 1139 , MZB 32121–32124 , Figs 147A–H View FIGURE 147 ), Rio di Bocca d’Asino: 3 valves ( BD 1140 ). Maximum width of the valves: 1.5 / 1.9 / 1.8 mm .

Description. Head valve semicircular. Intermediate valve broadly rectangular (W/L = 1.50–1.83), carinate in anterior profile, anterior margin almost straight, side margins rounded, posterior margin almost straight to slightly concave at both sides of prominent apex, projecting slightly outside posterior margin, jugal area large, lateral areas slightly raised, poorly separated from central area. Tail valve semicircular, anterior margin straight, mucro subcentral, poorly developed.

Tegmentum covered with densely spaced, small, flat, roundish/oval granules, arranged in arcuate rows,sometimes less visible on JA; granules fairly regular, with a central megalaesthete surrounded by 6–10 micraesthetes.

Articulamentum only slightly larger than tegmentum in intermediate valves, trapezoidal and widely separated apophyses just more expanded in tail valves, insertion lamina reduced to narrow band in head valve, slit formula 5 / 1 / 6–10, teeth irregular, roughed dorsally.

Remarks. This species was described by Bałuk (1971, 1984) upon many small valves from the Middle Miocene (Badenian) of Korytnica ( Poland). The species was also reported by Laghi (1977), Dell’Angelo et al. (2016) from the Miocene (Tortonian) of N. Italy, and Ruman & Hudácková (2015) from the Middle Miocene of Slovakia.

There is a certain variability in the shape of intermediate valves, with the apex sometimes very pronounced and projecting slightly outside posterior margin (e.g., Bałuk 1984, pl. 11, fig. 3).

Comparisons. Craspedochiton minutulus Bałuk, 1971 differs from the other Craspedochiton spp . described here mainly by its more regular sculpture, with granules arranged in arcuate rows, different from the irregular granules of variable size, more or less coalescing, shown by the other Craspedochiton spp .

Distribution. Middle Miocene: Paratethys (Langhian-Serravallian): Slovakia: Devínska Nová Ves, Rohožník ( Ruman & Hudácková 2015), Poland: Korytnica, Lychów, Węglin, Weglinek ( Bałuk 1971, 1984; Macioszczyk 1988). Upper Miocene: Proto-Mediterranean Sea (Tortonian): Po Basin, Italy: Montegibbio, Rio di Bocca d’Asino ( Laghi 1977; Dell’Angelo et al. 1999, 2016).