Potamides sp.

Harzhauser, Mathias, Guzhov, Aleksandr & Landau, Bernard, 2023, A revision and nomenclator of the Cainozoic mudwhelks (Mollusca: Caenogastropoda: Batillariidae, Potamididae) of the Paratethys Sea (Europe, Asia), Zootaxa 5272 (1), pp. 1-241 : 79-80

Potamides sp.

Cerithium nassoides Koenen, 1891 — Ondrejíčková & Seneš 1965: 174, pl. 3, figs 28–29 [non von Koenen, 1891].

Cerithium tenuicosta Koenen, 1891 — Ondrejíčková & Seneš 1965: 174, pl. 3, fig. 30 [non von Koenen, 1891].

Bittium granuliferum ( Koenen, 1891) — Ondrejíčková & Seneš 1965: 176, pl. 3, figs 31–32 [non von Koenen, 1891]. Cerithium rarinodosum Koenen, 1891 — Ondrejíčková & Seneš 1965: 174 [non von Koenen, 1891].

Material. Several specimens described by Ondrejíčková & Seneš (1965) from the drillings at Štúrovo ( Slovakia) were stored in the Geological Institute of the Slovak Academy of Sciences (Bratislava, Slovakia) and later moved to the Slovak Natural History Museum, Bratislava). The specimens, however, seem to be lost.

Description. Moderately slender conical shell; apical angle ~28°. Early teleoconch whorls convex with prominent, beaded spiral cord at abapical suture, slightly weaker, beaded mid-whorl spiral cord and delicate spiral cord at adapical suture. Later teleoconch whorls moderately convex. Lower two spiral cords attain about same strength, forming subcylindrical periphery. Beads vaguely axially arranged. Adapical spiral cord always slightly weaker. Beads of adapical spiral cord causing slightly wavy, deeply incised suture. Last whorl not preserved.

Discussion. This is a poorly known species, documented by few specimens from the drillings at Štúrovo ( Slovakia). The mode of sculpture formation and the small size suggest a closer relation with Potamides fraterculus (Mayer, 1878) than with Potamides lamarckii Brongniart, 1810 . It differs from Potamides fraterculus in its more prominent beads, the wider interspaces between the spiral cords and the prominent spiral cords on the base. The specimens and spire fragments were identified by Ondrejíčková & Seneš (1965) as Cerithium nassoides von Koenen, 1891 , Cerithium tenuicosta von Koenen, 1891 , Cerithium rarinodosum von Koenen, 1891 and Bittium granuliferum (von Koenen, 1891) , all originally described from the Rupelian of the North Sea Basin. These identifications are dubious due to the large paleogeographic distance between the occurrences and wide stratigraphic gap. Indeed, the similarity of the Rupelian North Sea species with the Egerian Potamides from Slovakia is superficial at best, and the North Sea Basin species represent Cerithiidae and Plesiotrochidae (see von Koenen 1891: pl. 45, figs 13–14, 18–19, 46, fig. 7). Cerithium nassoides von Koenen, 1891 is preoccupied by Grateloup, 1832 and G. B. Sowerby II, 1855 (we have not checked the North Sea Basin literature if a replacement name is already proposed).

Distribution. Endemic to the Central Paratethys Sea and only known from one sample in the M3 drilling (486 m) at Mužla at Štúrovo ( Slovakia).

Central Paratethys. Egerian (late Oligocene/Early Miocene): South Slovakian Basin: Štúrovo ( Slovakia) ( Ondrejíčková & Seneš 1965).

Genus Theodisca nov. gen.

Type species. Cerithium theodiscum Rolle, 1856 ; Middle Miocene , Badenian, Austria, Central Paratethys Sea .

Etymology. Referring to the type species Cerithium theodiscum Rolle, 1856 .

Diagnosis. Small, conical to elongate pupoid shell with conical to cyrtoconoid spire and subcylindrical whorls. Sculpture with two dominant adsutural beaded spiral cords, often adjoined by weaker central spiral cord. Last whorl with slightly angulated base and peribasal spiral cord. Aperture with slightly flaring, weakly angulated outer lip. Inner lip forming narrow pseudumbilicus with narrow siphonal fasciole. Narrow siphonal canal.

Description. Small, conical to elongate pupoid shell with conical to cyrtoconoid spire and subcylindrical whorls. Protoconch conical to turreted of two to three convex whorls. Early teleoconch whorls decreasing in convexity, angulated at periphery close above abapical suture. Sculpture of two prominent, beaded adsutural cords, whorl smooth between and concave in profile, with weak mid-cord developing on late teleoconch whorls on some specimens. Beads axially arranged, occasionally forming straight to weakly opisthocline axial ribs. Sculpture often fading out during ontogeny, resulting in weakly sculptured last whorls. Last whorl convex to subcylindrical with rapidly contracting base and one or two distinct peribasal spiral cords; no ventrolateral varix. Aperture moderately wide, ovoid. Columella excavated. Inner lip forming distinct rim, often with narrow pseudoumbilicus between lip and narrow, twisted siphonal fasciole. Anal canal indistinct. Outer lip weakly thickened, twisted at fasciole. Siphonal canal incised, short, relatively narrow, bent to the left.

Stratigraphic and geographic range. Burdigalian: Proto-Mediterranean Sea ( Turkey, Spain) and Central Paratethys Sea ( Austria); Langhian: Central Paratethys Sea ( Austria, Bulgaria, Hungary, Poland, Ukraine, Romania), Northeastern Atlantic ( France). Serravallian: Proto-Mediterranean Sea ( Turkey), Central Paratethys Sea ( Austria, Bulgaria, Hungary, Poland, Romania, Slovakia, Czech Republic), Eastern Paratethys Sea (Azerbaijan, Georgia, Kazakhstan, Moldova, Russia, Ukraine); Tortonian: Proto-Mediterranean Sea ( Italy), Eastern Paratethys Sea (Azerbaijan, Bulgaria, Georgia, Moldova, Romania, Russia, Ukraine). Early to Late Pliocene: Mediterranean Sea ( Italy, Greece), eastern Paratethys (Azerbaijan, Georgia). Early to Middle Pleistocene: Mediterranean Sea ( Italy).

Included species. Cerithium theodiscum Rolle 1856 , Early Miocene (Burdigalian) to Late Miocene (Tortonian), Central Paratethys Sea, Proto-Mediterranean Sea. Cerithium cicur Zhizhchenko, 1934 , Middle Miocene (Chokrakian), Eastern Paratethys Sea. Potamides biseriatus Friedberg, 1914 , Middle Miocene (Volhynian) to Late Miocene (Bessarabian), Central and Eastern Paratethys. Potamides azerbajdjanicus K.A. Ali-Zade, 1940 , Pleistocene (Akchagylian), Eastern Paratethys Sea. Cerithium graecum Deshayes, 1832 , Early Pliocene (Zanclean) to Middle Pleistocene (Calabrian), Mediterranean Sea. Cerithium etruscum Mayer, 1864 , Early Pliocene (Zanclean) to Early Pleistocene (Gelasian), Mediterranean Sea.

Pirenella simplicior Peyrot, 1938 is a potential representative of this genus in the Langhian of the Loire Basin, which is morphologically close to Theodisca biseriata due to its reduced sculpture, angulated base and elongate pupoid outline (see Peyrot, 1938: 154, pl. 3, figs 35, 42). Note that Glibert (1949) introduced Potamides dujardini as replacement name for Cerithium pulchellum Dujardin, 1837 , which was variously preoccupied ( Adams 1850; J. de C. Sowerby 1832) (see Peyrot, 1938: 153, pl. 3, figs 23, 28; Glibert 1949: 134, pl. 9, figs 2a, 2b). Glibert (1949) listed also Pirenella pulchella simplicior Peyrot, 1938 as synonym of Potamides dujardini , in which case Peyrot's name would have priority. As we have not studied any material from the Loire Basin, we cannot clarify this situation, but follow Lozouet (1986) who considered Potamides dujardini to be closely related with Potamides hartbergensis (= P. fraterculus ).

Ecology. Theodisca is documented from littoral to shallow sublittoral marine environments and from brackish coastal mudflats (see discussion on T. biseriata below).

Discussion. All species described herein in Theodisca have been treated as Potamides by previous authors. Nevertheless, already Lozouet (1986) had separated this species group from the species group including the type species of Potamides . Potamides differs especially in its strongly convex early teleoconch whorls, which lack the angulated periphery of Theodisca and develops conical shells. Both genera have a tripartite sculpture on early teleoconch whorls, but Potamides does not reduce the central spiral cord as frequently seen in Theodisca . Moreover, the last whorl of Potamides is more convex and lacks the smooth peribasal cord of Theodisca .

This genus comprises species, which were treated by Lozouet (1986) as “groupe de P. theodiscus – P. graecus ” and Lozouet (1986) assumed that these species were ancestral to Pirenella conica (de Blainville, 1829) . Similarly, Brunetti (2013) separated this species group from Potamides Bruguière, 1792 and placed it in Cerithideopsilla Thiele, 1929 (= Pirenella Gray, 1847 ). This would result in Miocene Mediterranean–Paratethyan roots of Pirenella , which conflicts with molecular and fossil data that suggest an IWP origin of the genus during the Early Miocene ( Ozawa et al. 2015). Moreover, Miocene Pirenella species from Indonesia, Japan and Sri Lanka, can morphologically be related to modern clades ( Ozawa et al. 2015: 216; Reuter et al. 2021), whereas the European Miocene species are only superficially similar to Pirenella conica . Fifteen of the 16 Pirenella species described by Reid & Ozawa (2016) develop three spiral cords of beads of more or less same strength. Only Pirenella conica is known to develop morphs with two spiral cords. Thus Pirenella , basically develops a tripartite sculpture, which is maintained to the last whorl. In contrast, in Theodisca the presence of a fully developed central spiral cord is exceptional. Similarly, the presence of a ventrolateral varix is typical for 15 out of 16 Pirenella species (weak or obsolete only in P. conica ), but is absent in Theodisca . Moreover, all Pirenella species are distinctly larger ranging around 20 to 50 mm in height, whereas Theodisca comprises small species of about 10 to 20 mm on average. Consequently, the similarity between the European Theodisca species and Pirenella conica is an example of convergence.