Hydrobia (s.l.) galatoniana, 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 : 4-5

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

( Figs 2A, B ; 3 A-C)

urn:lsid:zoobank.org:act:81

Hydrobia sp . – Esu et al. 1994: 189, pl. 2, fig. 4b.

TYPE MATERIAL. — Holotype: MPUR7-3897 ( Fig. 3A ), H = 4.9 mm, W = 2.3 mm . — Paratypes: MPUR7-3898/2 , 4198/1 , 4211/90, 4200/40.

DERIVATION OF NAME. — Named after 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, elongately conical, with up to 6 ¼ whorls, moderately convex to slightly flattened in the middle, often providing a faint angulation in the lower part of the whorl. Aperture ovate to quadrangular ovate, adapically rounded to barely angulate. Umbilicate.

DESCRIPTION

Shell small-sized, solid, elongately conical, more or less turreted, with up to 6 ¼ regularly increasing whorls, moderately convex to slightly flattened in the middle, often providing a faint angulation in the abapical part and a step-like margin adapically, in proximity of the suture. Suture incised, deep. Last whorl high just under two thirds of shell height. Protoconch of c. 480 µm maximum diameter, smooth, consisting of one and a quarter slightly convex whorl ( Fig. 2B ). Teleoconch glossy, with thin, prosocline to nearly orthocline and rather regularly spaced growth lines gradually appearing after the protoconch. Aperture ovate to quadrangular-ovate, adapically rounded to barely angulate, sometimes slightly thickened inside along the outer lip; peristome simple, continuous, columellar lip smoothly concave, adherent partially to the last whorl, outer lip slightly arched in lateral profile. Sometimes transverse, more or less raised wrinkles, irregularly spaced, occur on the last whorl just before the aperture ( Figs 2A ; 3 Ac, Bc). Umbilicus open, narrow, and deep. Range dimensions: H = 4.1-5 mm, W = 2.1-2.4 mm, H/W = 1.95-2.08.

REMARKS

The shell shape of Hydrobia (s.l.) galatoniana n. sp. shows a certain degree of variability, varying from more ( Fig. 3B ) to less turreted ( Fig. 3C ), with moderately convex to slightly flattened whorls, and ovate ( Fig. 3 Ba) to quadrangularovate aperture ( Fig. 3 Aa, Ca). Comparisons of the study material with several members of Hydrobiidae from the literature, and those stored in the rich malacological collection at the Senckenberg Museum of Frankfurt a. M., showed similarity mainly to two species: Hydrobia dubuissonii ( Bouillet, 1834) and Hydrobia andreaei O. Boettger in Degrange-Touzin, 1892. Bouillet (1834: captions to pl. 18, fig. 14) gave a good description of H. dubuissonii from the Oligocene of the type locality (Aurillac, France), whilst the accompanying picture is unclear. Lozouet & Maestrati (2012: fig. 183.1-8) supplied good illustrations of French specimens of this species from the Oligocene (Stampian) of the Paris Basin. Hydrobia dubuissonii from Oligocene deposits of France (Aurillac and Paris Basin), and Middle Oligocene (Rupelian) of Vieux-Jone, Belgium, stored at the Senckenberg Museum (SMF 12.1594c, ex coll. O. Semper), differs from H. (s.l.) galatoniana n. sp. in having a conical-pyramidal shape, a more acute spire with more prominent apex, whorls not stepped, narrower, more ovate and adapically more angled aperture, and a narrower umbilicus (cf. Esu & Girotti 2010: pl. 3, fig. 8; Lozouet & Maestrati 2012). Maximum dimensions (H = 4 mm, W = 2 mm) given by Bouillet (1834) for H. dubuissonii from the type-locality are on average smaller than those measured for the Galatone specimens (H = 4.1-5 mm, W = 2.1-2.4 mm). Hydrobia andreaei from Early Miocene localities of France, Cabanac (Pouquet), Aquitanian (SMF 245531/1-245532/1, coll. O. Boettger, ex Degrange-Touzin), Saucats (near Bordeaux), Aquitanian (SMF 245533/9, coll. O. Boettger), Lariey (Saucats), Aquitanian (SMF 245550/2, coll. O. Boettger), and Oligocene (Chattian, Cyrenenmergel) of ṙKolbsheim, Elsass (SMF 245534/24, coll. O. Boettger, ex A. Andreae) (cf. Degrange-Touzin 1892: 181), differs from H. (s.l.) galatoniana n. sp. in having a more cylindrical and elongate shell with more acute apical angle, a shallower suture, the last whorl slightly descending towards the aperture, restricted and provided with a faint ring-like varix close to the outer lip, a narrower and semiovate aperture, columellar margin slightly thickened and more oblique, outer margin well arched, a not deep umbilicus, and on average smaller size (H = 3.75-4.5, W = 1.62-1.75) (cf. Boettger in Degrange- Touzin 1892: pl. 5, figs 1-1c; Lozouet et al. 2001: fig. 9). Hydrobia (s.l.) galatoniana n. sp. is distinct from the coeval Hydrobia dubuissonii hydruntina Esu & Girotti, 2010, from the Upper Oligocene marls of the bauxite quarry at Otranto (Apulia) ( Esu & Girotti 2010: pl. 3, figs 1-7), in having a more cylindrical shell, more convex whorls, wider quadrangular-ovate aperture, and on average larger size (holotype of H. dubuissonii hydruntina: H = 3.8 mm, W = 2 mm; mean size: H = 4 mm, W = 2 mm). Quaggiotto & De Angeli (2016: fig. 3.1-3) illustrated some not well-preserved remains of Hydrobia cf. dubuissonii from the Lower Oligocene of Valle del Ponte (Vicenza, northeastern Italy). These specimens are clearly different from H. (s.l.) galatoniana n. sp. for their larger size (H = 7 mm), and more elongate and turreted shell shape.

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. 3. — A-C, Hydrobia (s.l.) galatoniana n. sp., Galatone (Lecce, Apulia), Late Oligocene: Aa-Ac, holotype MPUR7-3897; Ba-Bc, paratype MPUR7-3898/2a; Ca-Cb, paratype MPUR7-3898/2b. Scale bar: 2 mm.