Thericium posidoniaphilum, Harzhauser & Guzhov & Landau, 2025

Thericium posidoniaphilum sp. nov.

Figs 27F, 50A–C View FIGURE 50

Cerithium (Ptychocerithium) procrenatum Sacco— Sieber 1937: 493 (pars), pl. 24, fig. F3 [non Thericium procrenatum ( Sacco, 1895) ].

Cerithium crenatum procrenatum Sacco— Strausz 1962: 44 , pl. 9, figs 4–6 [non Thericium procrenatum ( Sacco, 1895) ].

Cerithium crenatum procrenatum Sacco, 1895 — Strausz 1966: 136, pl. 9, figs 4–6 [non Thericium procrenatum ( Sacco, 1895) ].

Cerithium (Ptychocerithium) procrenatum Sacco, 1895 — Bałuk 1975: 152, pl. 17, figs 17–19 [non Thericium procrenatum ( Sacco, 1895) ].

Type material. Holotype, NHMW 2023 View Materials /0040/0003, SL: 30.7 mm, MD: 9.9 mm, Steinebrunn ( Austria), illustrated in Sieber (1937: pl. 24, fig. F3) Figs 50A View FIGURE 50 1 –A View FIGURE 1 2 View FIGURE 2 ; paratype, NHMW 2023 View Materials /0048/0001, SL: 34.1 mm, MD: 11.7 mm, Gainfarn ( Austria) Figs 50B View FIGURE 50 1 –B View FIGURE 1 2 View FIGURE 2 ; paratype, NHMW 2023 View Materials /0048/0002, SL: 36.2 mm, MD: 10.5 mm, Mikulov (Czechia), Figs 50C View FIGURE 50 1 –C View FIGURE 1 2 View FIGURE 2 ; NHMW/1851 View Materials /9913/0077, SL: 26.3 mm, MD: 7.5 mm, Steinebrunn ( Austria), Fig. 27F.

Additional material. 3 spec., NHMW 1851 View Materials /0013/0077a, Steinebrunn ( Austria) ; 4 spec., NHMW 2023 View Materials /0049/0001, Gainfarn ( Austria) ; 9 spec., NHMW 1853 View Materials /0003/0148, Gainfarn ( Austria) ; 8 spec., NHMW 1860 View Materials /0001/0266, Mikulov ( Czechia) .

Type locality. Steinebrunn ( Austria), Vienna Basin .

Type stratum. Silt and sand of the Baden Formation.

Age. Middle Miocene, middle Badenian (late Langhian).

Etymology. Referring to the assumed preference for sea grass meadows ( Posidonia = Neptune grass; - philum, latinized Greek for loving).

Diagnosis. Medium-sized, moderately slender shell with prominent, swollen axial ribs on early teleoconch whorls and coarse, somewhat irregular sculpture of primary and secondary spiral cords with moderately prominent tubercles to beads. Aperture oblique with crenulated outer lip and short, twisted siphonal canal.

Description. Medium-sized, moderately slender shell of about 11 teleoconch whorls, attaining ~ 30–40 mm in height; apical angle 30–35°. Protoconch unknown. Early teleoconch whorls weakly convex with prominent, swollen axial ribs separated by interspaces of about same width. Spiral sculpture of several primary cords and weaker secondary threads forming weak, spirally elongate tubercles at intersections with axial ribs at around third teleoconch whorl. Delicate subsutural spiral cord with weak to obsolete beads. Later whorls weakly convex to subcylindrical. Axial sculpture initially predominant weakens abapically, except for two distinct varices on spire whorls, spirals gradually become predominant. Three primary spiral cords bearing rounded to pointed tubercles at sculptural intersections, close-set enough in some specimens to be described as beading; mid-whorl cord slightly more prominent; fourth beaded cord appears at abapical suture on penultimate whorl. Two narrow secondary spirals intercalated on narrow, slightly concave subsutural ramp between finely beaded subsutural cord and first primary cord. Additional secondary and tertiary threads in interspaces between other primaries on later whorls. Suture deeply incised on early teleoconch whorls, slightly shallower on later whorls, undulating. Last whorl high, weakly convex, attaining ~40% of total height. Base weakly constricted with prominent primary and secondary spiral cords. Aperture ovate, moderately wide, strongly oblique. Columella broadly and shallowly excavated. Columellar callus forming narrow to moderately broad, weakly thickened rim, sharply delimited from base. Anal canal deeply incised, narrow, prominent parietal denticle. Outer lip not thickened, crenulated. Siphonal canal moderately narrow, twisted, strongly deflected to the left.

Discussion. This species is reminiscent of Thericium poetzleinsdorfense ( Sacco, 1895) and T. grundense ( Sacco, 1895) with which it was confused so far in the literature and in the collection of the NHMW. Thericium posidoniaphilum sp. nov. differs from T. poetzleinsdorfensis and T. grundense in its broader and more swollen axial ribs, which are wider-spaced and by the poorly defined tubercles. In addition, the somewhat irregular shape of the spire and the undulating suture distinguish T. posidoniaphilum from T. poetzleinsdorfensis . Thericium chamaeleo sp. nov. is superficially similar but differs distinctly by the predominant spiral sculpture on early teleoconch whorls. Within the Paratethyan representatives of the Thericium crenatum group, this species is characterized by its irregular and coarse sculpture. Moreover, the aperture is slightly more oblique. Thericium procrenatum ( Sacco, 1895) , from the Burdigalian of Italy, is distinguished by its mid-whorl angulation and more regular sculpture of larger, wider-spaced tubercles.

Thericium posidoniaphilum seems to have occurred in seagrass whereas T. poetzleinsdorfense is documented from sandy inner neritic environments. This might point to habitat segregation within this group.

Paleoenvironment. The frequent occurrence at Steinebrunn and Gainfarn ( Austria) suggests inner neritic environments with seagrass cover ( Zuschin et al. 2007; own data M.H.).

Distribution. Only known from the Badenian (Langhian) of the Central Paratethys Sea.

Central Paratethys. Badenian (Middle Miocene): Korytnica Basin: Korytnica ( Poland) ( Bałuk 1975); Vienna Basin: Gainfarn, Steinebrunn ( Austria), Mikulov ( Czechia) (hoc opus); Pannonian Basin: Budapest (Illés street) ( Hungary) ( Strausz 1966).