Hydrobia (s.l.) ionica, Hartmann, 1821

Esu, Daniela & Girotti, Odoardo, 2019, Two new oligohaline Hydrobia (s. l.) (Caenogastropoda) from the transitional Upper Oligocene Galatone Fm (Apulia, Southern Italy), Geodiversitas 41 (1), pp. 1-9 : 6-7

Hydrobia (s.l.) ionica n. sp.

( Figs 2C, D ; 4 A-C)

urn:lsid:zoobank.org:act:8D0FEDB0-

Pseudamnicola (Staja) sp. – Esu et al. 1994: 189, pl. 2, fig. 4a.

TYPE MATERIAL. — Holotype: MPUR7-3899 ( Fig. 4 A ), H = 4.5 mm, W = 2.5 mm. — Paratypes: MPUR7 -4197/2, 4199/1, 3900/40.

DERIVATION OF NAME. — Named after the Ionian Sea, whose shoreline is near the type locality.

TYPE HORIZON. — Limy mudstone layers of Galatone Fm at Galatone ( Esu et al. 1994; Bossio et al. 1998).

TYPE LOCALITY. — Galatone (Lecce, Apulia, Italy) (40°8’27.03”N, 18°03’0.37”E).

TYPE AGE. — Chattian (Late Oligocene).

DIAGNOSIS. — Small-sized shell, ovately conical, with up to 5 slightly convex whorls, the last large and elongate. Aperture pear-shaped, relatively high and elongate, adapically barely angulate, somewhat flared and slightly thickened inside. Umbilicus slit-like.

DESCRIPTION

Shell small, solid, thick-walled, ovately conical, with up to 5 slightly convex whorls, the last large, elongate, exceeding two-thirds of shell height. Early whorls slowly increasing, the last faster and somewhat descending ( Figs 2C ; 4 Ab, Ba). Suture shallow, oblique between the penultimate and ultimate whorl. Protoconch of c. 410 µm maximum diameter, smooth, consisting of one slightly convex whorl. Boundary to teleoconch distinct by the formation of closely spaced growth lines ( Fig. 2D ). Teleoconch glossy, with very delicate and thin prosocline growth lines. An axial swelling occurs sometimes in the last whorl towards the aperture. Aperture pear-shaped, high, elongate, adapically barely angulate and abapically rounded, somewhat flared and slightly thickened inside; peristome continuous, columellar lip almost completely adherent to the last whorl, outer lip straight in lateral profile. Umbilicus slit-like. Range dimensions: H = 4-4.5 mm, W = 2.5-2.7 mm, H/W = 1.48-1.8.

Provisionally, Esu et al. (1994) assigned this stout form to the subgenus Pseudamnicola (Staja) Brusina, 1897 , currently considered a separate genus of the family Hydrobiidae ( Harzhauser et al. 2015; MolluscaBase 2018b). Examination of further material allowed distinguishing this species from Staja, which is a Miocene Eastern European taxon rich in several species (cf. MolluscaBase 2018b), characterised by a very small size (dimensional range: H = 1.6-2.5 mm, W = 1-1.2 mm) and a mainly conical shell with regularly growing whorls (cf. Brusina 1897; Jekelius 1944). The assignment of ionica n. sp. to the same genus as galatoniana n. sp. is likely supported by similar conchological characters between the two species, such as hydrobioid shell shape with slightly convex whorls, last whorl higher, ovate-elongate and barely flared aperture, and smooth protoconch. Hydrobia (s.l.) ionica n. sp. differs from H. (s.l.) galatoniana n. sp. in having a more globose shell, a wider apical angle, a smaller protoconch, the last whorl proportionally wider and higher, the aperture more elongate, and a smaller H/W (max) ratio (1.8 vs 2.08). It differs from the coeval H. dubuissonii hydruntina from the Upper Oligocene marls of Otranto bauxite quarry ( Esu & Girotti 2010) in being conical-ovate in shape, in having a less acute spire, a proportionally higher last whorl and wider and more elongate aperture. Hydrobia dubuissonii from Oligocene deposits of France and Belgium (see above) differs from H. (s.l.) ionica n. sp. in having a conical-pyramidal shape, a more acute spire and a smaller and more ovate aperture.

Figures

FIG. 2. — A, B, Hydrobia (s.l.) galatoniana n. sp., Galatone (Lecce, Apulia), Late Oligocene, paratype MPUR7-4198: A, apical view of the shell; B, detail of the protoconch; C, D, Hydrobia (s.l.) ionica n. sp., Galatone (Lecce, Apulia), Late Oligocene, paratype MPUR7-4199: C, apical view of the shell; D, detail of the protoconch. SEM image. Scale bars: A, C, 500 µm; B, D, 200 µm.

FIG. 4. — A-C, Hydrobia (s.l.) ionica n. sp.,Galatone (Lecce,Apulia),Late Oligocene:Aa-Ac, holotype MPUR7-3899;Ba-Bc, paratype MPUR7-4197/2a; Ca-Cc, paratype MPUR7-4197/2b. Scale bar: 2 mm.