Lepidochitona subgranosa Bałuk, 1971

Lepidochitona subgranosa Bałuk, 1971

Fig. 127 View FIGURE 127

Lepidochitona subgranosa Bałuk, 1971, p. 460 , pl. 4, figs 1–5; Van Belle 1981, p. 74; Bałuk 1984, p. 289, pl. 7, fig. 4; Studencka & Studencki 1988, p. 40, pl. 2, figs 2, 4; Garilli et al. 2005, p. 136; Dell’Angelo et al. 2012, p. 63; Dell’Angelo et al. 2013, p. 90; Ruman & Hudácková 2015, p. 164; Dell’Angelo et al. 2016, p. 98, tab. 5; Dell’Angelo et al. 2018b, p. 52; Dell’Angelo et al. 2020b, p. 53, tab 9.

Type material. Holotype BkK-A26 (Bałuk collection), tail valve ( Fig. 127A View FIGURE 127 ).

Type locality. Korytnica , Holy Cross Mts. ( Poland) .

Type stage. Middle Miocene.

Material examined. No actual material available, only descriptions and illustrations from the literature.

Description. Head valve semicircular, posterior margin widely V-shaped. Intermediate valves broadly rectangular, anterior margin almost straight, side margins rounded, posterior margin almost straight, with well pronounced apex, lateral areas slightly raised. Tail valve triangular, flat, anterior margin almost straight, mucro subcentral.

Tegmentum uniformly covered with closely spaced, fine granules, arranged in intersecting, arcuate rows.

Articulamentum with teeth roughened on outside, slit formula 8 / 1 / 7, slit rays visible.

Remarks. Lepidochitona subgranosa Bałuk, 1971 is known only from the Middle Miocene of Poland, Korytnica ( Bałuk 1971, 1984), Nawodzice ( Figs 127C–D View FIGURE 127 ) and Rybnica ( Studencka & Studencki 1988).

The sculpture of the tegmentum is similar to that of Lepidochitona lepida ( Reuss, 1860) , the only difference is represented by the tail valve (triangular, flat, mucro subcentral, vs. semicircular, more elevated, mucro anterior to posterior in L. lepida ) [ Bałuk 1971, p. 460: “ Much less prominent granules and, primarily, a different shape and degree of convexity of the tail valve differ them from Lepidochitona lepida ”; Studencka & Studencki 1988, p. 40: “ The ornamentation of tegmentum in L. subgranosa resembles the sculpture of L. lepida , but the latter species has longer, triangular tail valve with posterior mucro, and 8 radial ribs at its head valve ( in adult specimens)”]. The tail valve figured by Studencka & Studencki 1988 ( Fig. 127D View FIGURE 127 ) shows the same triangular shape of the holotype of L. subgranosa , and so we confirm for the moment the attribution to the the latter species, pending the discovery of further material, also because there are no indications that the valve is “flat” as indicated (but not figured) in the original description

Laghi (1977) postulated that both Lepidochitona lepida and L. subgranosa are conspecific with the Recent species L. cinerea ( Linnaeus, 1767) , a hypothesis rejected by Bałuk (1984) as this cannot be evidenced when having only isolated valves. On the other hand Bałuk himself (1984) highlighted the remarkable similarity of the sculpture of the valves of this species with Lepidochitona canariensis ( Thiele, 1909) , and in the material from Korytnica there are also some plates “ with an ornamentation particularly fine and these specimens are fairly distinctly different than the rest ” ( Bałuk 1971: 460).

Comparisons. See Tab. 20 for further comparison with the other Lepidochitona spp . from the Paratethys considered in the present study.

Distribution. Middle Miocene. Central Paratethys (Langhian–Serravallian): Poland: Korytnica, Nawodzice, Rybnica ( Bałuk 1971, 1984; Studencka & Studencki 1988).