Plagioconus

Plagioconus hirmetzli (Kovács & Vicián, 2013)

Figs 30 E, 32H, 32I, 32J

2013 Leptoconus hirmetzli sp. n. —Kovács & Vicián, 62, figs 30–37.

Type material. Holotype HNHM PAL 2013.3.1 (Hungarian Natural History Museum), paratypes HNHM PAL 2013.4. 1, HNHM PAL 2013.5.1– PAL 2013.9.1 (Hungarian Natural History Museum) and private collection of Tamás Hirmetzl (Hungary), all from Letkés (Hungary); middle Miocene, Badenian (Langhian).

Illustrated material. Fig. 32 H: paratype, SL: 130 mm, MD: 34 mm, private collection of T. Hirmetzl; Fig. 32 I: paratype, SL: 67 mm, MD: 17 mm, private collection of T. Hirmetzl, Fig. 32 J: holotype, SL: 62 mm, MD: 21 mm, HNHM, PAL 2013.3.1; Fig. 30 E: SL: 114 mm, MD: 32.3 mm, private collection Anton Breitenberger (Bad Vöslau, Austria); all Letkés (Hungary).

Revised description. Large, elongate, slender, biconical shell with very high spire and strongly elongate last whorl; protoconch paucispiral. Early spire whorls weakly angulate, tuberculate; later spire whorls high and convex. Suture deeply incised; subsutural flexure very deep, moderately curved, strongly asymmetrical. Last whorl with rounded to subangulate shoulder; position of maximum diameter slightly below shoulder; straight sided to faintly concave, not constricted at base; smooth surface. Aperture very narrow with subparallel margins. Fasciole very weak, twisted; siphonal canal slightly reflected and long. No colour pattern preserved.

Shell measurements and ratios. Holotype: height (fragmentary): 62 mm, MD: 21 mm, spire angle: 31°, last whorl angle: 19°; paratype 1: height (fragmentary): 132 mm, MD: 42 mm, spire angle: 38°, last whorl angle: 18°; paratype 2: height (fragmentary): 130 mm, MD: 34 mm, spire angle: 35°, last whorl angle: 21°.

Discussion. This is a very rare species, which is only known so far from its early Badenian type locality Letkés in Hungary. Due to the peculiar morphology, Kovács & Vicián (2013) placed the species in Leptoconus Swainson, 1840. They referred to the comparably elongate and slender Leptoconus milneedwardsi (Jousseaume, 1894), which is an extant species in the Indo-West Pacific Region, and to L. aratispira (Pilsbry, 1905), from Pleistocene of Japan. Aside from these two extremely elongate species, Leptoconus species, like the extant type species Leptoconus amadis (Gmelin, 1791), have low conical spires. All develop angulated whorls, tend to have concave adapical parts of the spire whorls and many species have sculptured last whorls. The high and convex spire whorls of Plagioconus hirmetzli, the deep suture and smooth shell surface do not support the placement in Leptoconus. Therefore, we consider the similarity between the Miocene species with the extant L. milneedwardsi to represent a striking case of convergent evolution and consider it an extraordinarily high spired Plagioconus species comparable with Plagioconus marii (Sacco, 1893).

Paleoenvironment. The locality Letkés comprises a mixed assemblage of partly reworked taxa (Kovács & Vicián 2013); the frequent occurrence of corals suggests a shallow marine depositional environment.

Distribution in Paratethys. Badenian (middle Miocene). Pannonian Basin: Letkés (Hungary) (Kovács & Vicián 2013).