Thericium subcostatum ( Bałuk, 1975 )

Thericium subcostatum ( Bałuk, 1975)

Figs 58A–C View FIGURE 58

* Hemicerithium (Hemicerithium) subcostatum View in CoL sp. n. — Bałuk 1975: 154, pl. 18, figs 1–3.

Hemicerithium subcostatum Bałuk, 1975 View in CoL — Bałuk 2006: 198, pl. 8, fig. 7.

non Hemicerithium (Hemicerithium) subcostatum Bałuk, 1975 View in CoL — Švagrovský 1981: 134, pl. 42, fig. 1 [= Ptychocerithium bronnii

( Naumann, 1852)].

Type material. Holotype Z. PAL. U.W. No BkK-G 285 , SL: 7.5 mm, MD: 3.7 mm, Paleontological Institute of the Warsaw University ( Poland), illustrated in Bałuk 1975: 154, pl. 18, fig. 1, Korytnica ( Poland), Middle Miocene, Badenian, Figs 58B View FIGURE 58 1 –B View FIGURE 1 2 View FIGURE 2 . Paratype BkK-G 286 , SL: 4.3 mm, MD: 2.2 mm, Korytnica ( Poland), illustrated in Bałuk (1975: pl. 18, fig. 2). Fig. 58C View FIGURE 58 .

Illustrated material. BkK-G 1198, SL: 9.8 mm, MD: 4.4 mm, Korytnica ( Poland), illustrated in Bałuk (2006: pl. 8, fig. 7). Figs 58A View FIGURE 58 1 –A View FIGURE 1 2 View FIGURE 2 .

Revised description. Small, pupoid shell of up to seven teleoconch whorls, attaining ~ 10 mm in height; apical angle 40–55°. Protoconch unknown. Early teleoconch whorls low, convex. Subsequent whorls rapidly increasing in height, with faint subsutural collar, weakly shouldered below mid-whorl, convex below, suture weakly incised, linear. Poorly delimited, broad axial ribs forming indistinct tubercles at shoulder. One weak varix per whorl may occur. Spiral sculpture of numerous narrow spiral cords separated by narrow grooves. Last whorl ~52% of total height, with relatively broad, steep, slightly concave subsutural ramp, weakly angled at rounded shoulder, convex below; axial ribs subobsolete, except at shoulder forming low, axially elongated tubercles; spiral sculpture of narrow, flattened cords of weak primary to tertiary strength; more irregular in some specimens. Base convex with spiral sculpture continuing over base and short, twisted fasciole. Aperture wide, ovate. Columella broadly and moderately excavated. Columellar callus forming thin, narrow rim. Anal canal weakly incised, small parietal swelling. Outer lip thin. Siphonal canal moderately short, wide, slightly deflected to the left.

Discussion. Thericium subcostatum is an outlier within the Paratethyan cerithiids and there are no similar species. It might belong to the extant Thericium lividulum -group, which comprises very similar morphotypes on the Canary Islands (e.g., https://www.conchology.be/?t=116&aphia=139060&uniquenumber=216812) but also in Pliocene Mediterranean assemblages (e.g., Landau et al. 2004: pl. 1, figs 13–14).

This species was placed in Hemicerithium by Bałuk (1975, 2006) and Švagrovský (1981), but the specimens lack characteristic features of this genus, such as a conical shell with angulated whorls and varices. Moreover, the incised anal canal places this species in Cerithiidae rather than in Plesiotrochidae . Cerithium zebrum Kiener, 1841 is a morphologically similar Cerithiidae species within the modern IWP fauna (see Houbrick 1993).

Paleoenvironment. Unknown.

Distribution. Badenian of the Central Paratethys Sea.

Central Paratethys. Badenian (Middle Miocene): Korytnica Basin: Korytnica ( Poland) ( Bałuk 1975, 2006).