The Architectonicidae and Mathildidae (Gastropoda, Heterobranchia) of the Miocene Paratethys Sea-victims of the Miocene Climatic Transition Author Harzhauser, Mathias 0000-0002-4471-6655 Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria. mathias. harzhauser @ nhm-wien. ac. at; https: // orcid. org / 0000 - 0002 - 4471 - 6655; mathias.harzhauser@nhm-wien.ac.at Author Landau, Bernard 0000-0002-4471-6655 Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria. mathias. harzhauser @ nhm-wien. ac. at; https: // orcid. org / 0000 - 0002 - 4471 - 6655; & Naturalis Biodiversity Center, P. O. Box 9517, 2300 RA Leiden, Netherlands; Instituto Dom Luiz da Universidade de Lisboa, Campo Grande, 1749 - 016 Lisboa, Portugal; and International Health Centres, Av. Infante de Henrique 7, Areias São João, P- 8200 Albufeira, Portugal. bernardmlandau @ gmail. com; https: // orcid. org / 0000 - 0002 - 7768 - 8494 & Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria. mathias. harzhauser @ nhm-wien. ac. at; https: // orcid. org / 0000 - 0002 - 4471 - 6655; mathias.harzhauser@nhm-wien.ac.at text Zootaxa 2023 2023-11-14 5370 1 1 74 https://www.mapress.com/zt/article/download/zootaxa.5370.1.1/52270 journal article 10.11646/zootaxa.5370.1.1 1175-5334 10147814 48903495-7C6C-46E4-9B1B-D6A2F2781873 Heliacus globosus nov. sp. Figs 4L , 11B 1 –B 3 Type material. Holotype NHMW 1907 /0328/1959a, SL: 4.9 mm , MD: 10.7 mm , M̂llersdorf ( Austria ), Figs 4L , 11B 1 –B 3 . Type locality. Möllersdorf ( Austria ), Vienna Basin . Type stratum. Silty clay of the Baden Formation. Age. Middle Miocene, middle Badenian (Langhian). Etymology. Latin globosus [= globular, spherical], referring to the rounded periphery. Diagnosis. Medium-sized, solid shell with convex spire whorls and rounded periphery, characterized by relatively broad adapical MC, deep position of LPC and IPC forming weak angulation closely below LPC. Description. Medium-sized, solid, turbinid shell with moderately elevated, gradate spire and rounded periphery. Protoconch heterostrophic, medium-sized of 1.2 visible whorls (diameter 1.2 mm ). Teleoconch of 3.25 whorls. First teleoconch whorl with finely beaded SSC, beaded UPC and LPC and two poorly defined beaded MCs. SSC and MCs increasing in strength on subsequent whorl; adapical MC nearly as strong as SSC. Weaker spiral cord of beads intercalated between MCs. On second whorl secondary spiral row of beads intercalated between UPC and LPC. Abapically, beads becoming lower, subquadratic on last two whorls, and indistinct close to aperture. Periphery rounded without angulation or keel. UPC slightly more prominent forming periphery, LPC just below forming weak angulation. Whorls attached to LPC. Base weakly convex. LPC placed just medial to periphery in basal view. IPC distinct, followed by seven faintly beaded spiral cords on basal field, widening towards umbilicus. UC moderately prominent, slightly overhanging umbilicus, delimited from basal field by shallow narrow groove. Umbilicus cylindrical, moderately narrow (25% of total shell diameter). Umbilical wall with delicate opisthocyrt growth lines. Aperture moderately large, circular, no CG and PG developed. Discussion. Although represented by a single specimen, it is distinct enough to warrant formal description. Heliacus globosus nov. sp. is characterized by the position of the LPC slightly below the UPC and the strongly convex last whorl. Heliacus radiatus ( Borson, 1821 ) from the Oligocene of the Colli Torinesi might be a related species and agrees especially in the sculpture of the spire whorls. It is distinguished from Heliacus globosus in its much wider umbilicus and the prominent axial folds on the basal field (see Pavia 1976: pl. 1, figs 6a–c). Among extant Heliacus species , Heliacus maduernsis (Schepman, 1909) and Heliacus stramineus ( Gmelin, 1791 ) have comparable shell outlines with rather reduced peripheral keels, rounded periphery, convex dorsal side of the last whorl and circular aperture. These Indo-West Pacific species both differ from H. globosus in their more delicate sculpture. The Pliocene to Recent Mediterranean Heliacus fallaciosus (Tiberi, 1872) [= Heliacus subvariegatus (d’Orbigny, 1852) ] differs in its more angulated periphery, the higher position of the LPC and the funnel-shaped umbilicus ( Melone & Taviani 1985 : figs 31–33; Chirli 2013 : pl. 5, figs 7–12). Paleoenvironment. The occurrence in the Baden Formation suggests middle to outer neritic water depths ( Kranner et al. 2021 ). Distribution. Only known from the Langhian equivalent of the Badenian of the Central Paratethys Sea. Central Paratethys Sea. Middle Miocene (Badenian): Vienna Basin : M̂llersdorf ( Austria ).