Leptochiton sulci ( Bałuk, 1971 )

Leptochiton sulci ( Bałuk, 1971) View in CoL

Fig. 31 View FIGURE 31

Lepidopleurus sulci Bałuk, 1971, p. 455 View in CoL , pl. 2, figs 1–4; Bałuk 1984, p. 285, pl. 2, figs 1–3, pl. 3, figs 1–2, pl. 4, fig. 4;

Dell’Angelo & Palazzi 1989, p. 58. Lepidopleurus sulci View in CoL ?; Laghi 1977, p. 98. Leptochiton sulci View in CoL ; Van Belle 1981, p. 75; Macioszczyk 1988, p. 51, pl. 1, fig. 8a–b; Studencka & Dulai 2010, p. 261; Ruman &

Hudáčková 2015, p. 158, figs 2.2–2.6; Dell’Angelo et al. 2018b, p. 52, tab. 17; Dulai 2025a, p. 4, figs 3–8. Acanthochitona sp. Tomašových, 1998, p. 362, pl. 1, figs 7–8 ( fide Ruman & Hudáčková 2015). non Leptochiton ( Leptochiton) sulci ; Studencka & Studencki 1988, p. 38, pl. 1, fig. 4 [= Leptochiton cancellatus ( Sowerby,

1840), fide Studencka & Dulai 2010: 261).

Type material. Holotype BkK-A08 (Bałuk coll.), intermediate valve figured by Bałuk (1971: pl. 2, fig. 3).

Type locality. Korytnica , 24 km SSW of Kielce, southern slopes of the Holy Cross Mts ( Poland) .

Type stage. Middle Miocene.

Material examined. No actual material available, only descriptions and illustrations from the literature ( Figs 31A–H View FIGURE 31 ). Maximum width of valves: 2.5 / 3.2 / 2.5 mm.

Description. Head valve semicircular. Intermediate valves broadly rectangular, rounded in anterior profile, moderately elevated, anterior and posterior margins almost straight, apex not indicated, lateral areas slightly raised, with few growth ridges. Tail valve semicircular, mucro in central position, postmucronal slope slightly concave.

Tegmentum surface rough, granules disposed in longitudinal striae greater than those in radial ones. HV, LA and PMA sculptured with dense roundish granules arranged in radial striae (more than 50 in HV). CA and AMA sculptured with longitudinal series of roundish granules (CA 60–70,AMA ca. 50) joined by a narrow ridge, displaying a regular quincuncial pattern, with intercostal spaces twice lesser than their diameter. Each granule usually with 3–4 aesthetes of same size, normally aligned each other.

Articulamentum without insertion laminae, apophyses narrow and widely spaced.

Remarks. Leptochiton sulci ( Bałuk, 1971) is very similar to L. cancellatus ( Sowerby, 1840) , a well known species from the Mediterranean area, and was considered conspecific with L. cancellatus first by Laghi (1977), and later also by other authors ( Dell’Angelo & Palazzi 1989; Dell’Angelo & Smriglio 1999; Dell’Angelo & Silva 2003). Also WoRMS consider L. sulci as a synonym of L. cancellatus .

However, the two taxa show differences discernable ( Studencka & Dulai 2010; Ruman & Hudáčková 2015). In L. sulci , the granules are less dense, longitudinally arranged and joined by a narrow ridge, whereas in L. cancellatus they lay partially one upon the other; they differ also in the number and arrangement of the aesthetes: in L. cancellatus , each granule has a central megalaesthete with six lateral micraesthetes ( Studencka & Dulai 2010: fig. 2D), whereas there are only three-four aesthetes in L. sulci ( Bałuk 1984: pl. 3, fig. 1–2; Ruman & Hudáčková 2015: fig. 2.4b) ( Figs 31A–B, 31F View FIGURE 31 ), normally aligned with each other and more or less of the same size, difficult to separate into micraesthetes and megalaesthetes aesthetes. Moreover, the granules of neighbouring longitudinal ribs of L. sulci display a regular “quincuncial pattern” (see Bałuk 1984: pl. 3, figs 1–2; Ruman & Hudáčková 2015: fig. 2.4b) ( Figs 31A–B, 31F View FIGURE 31 ), not present in L. cancellatus (see Kaas 1981: fig. 10F; Studencka & Dulai 2010: fig. 2D). Schematic sculptural differences for both these species are well illustrated by Macioszczyk (1988: fig. 3). So, we consider the two species as different, following Bałuk (1971, 1984), Studencka & Dulai (2010) and Ruman & Hudáčková (2015).

Šulc (1934) described as Lepidopleurus cf. cancellatus (Capellini) a tail valve from Steinabrun in the Vienna Basin, not present at NHMW. The lack of figures does not permit to ascertain whether this valve truly pertains to Leptochiton cancellatus or instead to L. sulci , equally reported from the Parathetys.

The material examined from Varovtsi and Horodok ( Ukraine) includes many valves of a Leptochiton spp. which, after a thorough examination, do not agree with the attribution to L. boettgeri or L. sulci , but to L. cancellatus , corroborating the presence of this species from Varovtsi, as already reported by Studencka & Dulai (2010). Some of these valves are figured (see above, Figs 13M–T View FIGURE 13 ).

Comparisons. The characteristics of the sculpture of Leptochiton sulci agree with the belonging of the species to the Leptochiton cancellatus group, see Tab. 2.

Distribution. Middle Miocene: Central Paratethys (Langhian-Serravallian): Slovakia: Devínska Nová Ves, Rohožník ( Tomašových 1998; Ruman & Hudáčková 2015; this study); Hungary: Devecser ( Dulai 2025a); Poland: Korytnica, Węglin ( Bałuk 1971, 1984; Macioszczyk 1988).