Gastrocopta (Sinalbinula) sandbergeri, Stworzewicz & Prisyazhnyuk, 2006

Stworzewicz, Ewa & Prisyazhnyuk, Valentin A., 2006, A new species of Miocene terrestrial gastropod Gastrocopta from Poland and the validity of “ Pupa (Vertigo) suevica ”, Acta Palaeontologica Polonica 51 (1), pp. 165-170 : 167-169

Gastrocopta (Sinalbinula) sandbergeri sp. nov.

Figs. 1 , 2A–E .

1875 Pupa (Vertigo) suevica sp. nov.; Sandberger 1875: 654 (nomen nudum).

1877 Pupa suevica Sandberger ; Boettger 1877: 194, 195 (nomen nudum); non Leucochilus quadriplicatum mut. suevica Sandberger ; Boettger 1889: 279 [= Gastrocopta suevica ( Boettger, 1889) ].

1900 Pupa (Leucochilus) suevica Sandberger, 1875 ; Miller 1900: 398, pl. 7: 16.

1900 Pupa (Leucochilus) suevica var. minor ; Miller 1900: 398.

1919 Leucochila suevica (Sandberger, 1875) ; Gottschick and Wenz 1919: 13, pl. 1: 24–25.

1998 Gastrocopta suevica (Sandberger, 1874) ; Finger 1998: 19, pl. 8: D?, E, F.

1999 Gastrocopta suevica (Sandberger, 1875) ; Stworzewicz 1999: 164, fig. 62.

2000 Gastrocopta sp. ; Manganelli and Giusti 2000: pl. 6: 17.

Type material: Holotype: ISEA Ml/1033/98a and 19 paratypes ISEA Ml/1033/98b.

Type locality: The brown coal mine in Bełchatów(51 ° 15´N, 19 ° 20´E).

Type horizon: Beł−B horizon, Miocene, MN5.

Derivation of name: The species is named in honour of C.L. Fridolin Sandberger.

Additional material.—Steinheim, Miocene (MN7+8), 1 specimen MW, ex coll. Sandberger; 6 specimens IGS, Steklov’s material ex coll. Schlickum ; 1 specimen SMF 152387/3 ex coll. Boettger; 1 specimen MNHN 10815 ex coll. Cossmann.

Diagnosis.—The new species differs from all the remaining species of the subgenus Sinalbinula in having ovate−conical but always slender shell, a weak crest on the body whorl (with tendency to reduce) and generally weak apertural barriers. Specimens with somewhat larger apertural barriers show some similarity to G. nouletiana ( Dupuy, 1850) , but the elongate shell shape, smaller size, less convex whorls and distinctly weaker crest on the body whorl in G. sandbergeri easily separate the two species. The new species differs from the group of very slender species, such as G. didymodus ( Sandberger, 1858) , G. fissidens ( Sandberger, 1858) , and G. obstructa (Sandberger, 1874) , in that the parietal and angular portion of parietoangular tooth are partly fused (three latter species have a cylindrical shells with angular more or less distinctly separated from parietal). Compared to G. pseudotheeli Steklov, 1966 the new species has somewhat similar parietoangular tooth but the former species is distinguished immediately in having a solid crest on the body whorl.

Description.—Shell ovate−conical, usually slender, of 4.8– 5.5 moderately convex or somewhat flattened whorls. Surface irregularly, weakly striated or nearly smooth; striae sometimes more regular and more visible on the body whorl. Suture rather shallow. Body whorl equal to or slightly exceeding half shell height; last part of body whorl slightly ascending just before aperture, at the base somewhat narrowed, provided with a weak ridge situated a short distance behind the peristome (crest), rarely vestigial to absent. Umbilicus narrow, deep, open or partly covered with the body whorl. Aperture rounded triangular to almost circular, lip reflected. Parietal callus usually thinner than the rest of the lip. In aperture 7 teeth (rarely 6): parietoangular, infraparietal, columellar, basal and 3 (rarely 2) palatal. Parietoangular tooth: parietal portion short lamellate, subvertical, sometimes with thickened edge; angular portion somewhat shorter than parietal, thin and low, its inner end with slightly thickened tip, in front view bent palatalwards. Most specimens have a slight convexity situated on the left side of the middle part of parietoangular to make the angular portion triangular in outline. Infraparietal tooth as an elongate tubercle, situated half way between the parietoangular and parietal/columellar corners. Columellar tooth well developed, short lamellate, subhorizontal in front view, relatively deep−situated. Basal tooth knob−shaped, in basal or columellar/basal position. Among palatal teeth the lower is the biggest; upper very short; suprapalatal vestigial or absent. Callus at the base of palatal teeth developed to varying degrees; from nearly invisible in specimens from Steinheim to more or less distinct in specimens from Bełchatów.

Dimensions.—Measurements (see Table 1 for individual measurements and those of comparative material) of 20 specimens from Bełchatów (in mm); shell: H = 1.90–2.17, W = 1.02–1.09; aperture: h = 0.71–0.80, w = 0.66–0.77; H of body whorl = 1.08–1.25; number of whorls: 4.8–5.5.

Variability and comparative remarks.—Shell measurements indicate that Gastrocopta sandbergeri is rather variable in shell height, but the shell is always elongate. A weak crest is always visible in specimens from Steinheim but rarely in specimens from Bełchatów. Shells from Bełchatów have more convex whorls and somewhat more robust apertural barriers than those from Steinheim. Only one of the 20 specimens from Bełchatów lacks an infraparietal tooth. By contrast, in specimens from Steinheim it is the suprapalatal tooth that tends to get reduced. The Bełchatów specimens also have a distinct callus at the base of palatal teeth, particularly of the upper one.

Gastrocopta sandbergeri differs from G. nouletiana ( Dupuy, 1850) —even from small specimens and also those previously regarded as a slimmer form gracilidens —in the following characters: (1) more slender shell (H/W ratio in 20 nouletiana specimens = 1.55–1.88, mean 1.73; in 20 sandbergeri specimens = 1.80–2.16, mean 1.95); (2) distinctly weaker crest on the body whorl; (3) apertural barriers generally weaker developed. In some specimens of G. nouletiana from various localities the parietoangular tooth may be rather weakly developed, as in G. sandbergeri , but the shell shape and size easily separate the two species ( Fig. 2F ). The new species can not also be confused with Gastrocopta serotina Ložek, 1964 ( Fig. 2G ) as the latter species is most similar to G. nouletiana .

Compared to the group of species with very slender and cylindrical shells, such as G. didymodus ( Sandberger, 1858) , G. fissidens ( Sandberger, 1858) and G. pseudotheeli Steklov, 1966 ( Fig. 2I ), as well as G. theeli ( Westerlund, 1877) ( Fig. 2H ) – G. sandbergeri differs rather clearly in having a less slender, ovate shell, less convex whorls, a distinctly shallow suture and an infraparietal tooth present (cf. Prisyazhnyuk 1977). In addition, G. fissidens and G. pseudotheeli both have a very distinct crest. The parietal and angular portions of the parietoangular tooth in G. fissidens are partly separated, with the angular portion distinctly bent towards the palatal wall.

Another very slender species— G. obstructa (Sandberger, 1874) —differs from G. sandbergeri for the slender shell, the whorls which are fairly convex and distinctly oblique, and for the reduced apertural barriers (suprapalatal and infraparietal teeth absent). The columellar wall in G. obstructa is distinctly oblique, so that its upper section is deflected from the shell axis towards the parietoangular tooth, resulting in a very much narrowed parietal margin between the tooth and the columellar/parietal junction; the space is too narrow for an infraparietal tooth.

Gastrocopta sandbergeri sp. nov. is a rare species in Miocene deposits. It was hitherto known only from Steinheim am Albuch (as Pupa suevica Sandberger, 1875 ) dated from the Mid Miocene (Astaracian, MN7+8), hence its occurrence in Bełchatów (Beł−B horizon, Orleanian, MN5) shifted its stratigraphic range to the Lower/Mid Miocene limit.

Figures

Fig. 1. Pupa suevica sensu Sandberger (= Gastrocopta sandbergeri sp. nov.) from the Sandberger’s collection (MWNH−22−2), Miocene (Astaracian, MN7), Steinheim. Photograph by Fritz Geller−Grimm.

Fig. 2. A, B. Pupa suevica sensu Sandberger (= Gastrocopta sandbergeri sp. nov.) from Steinheim, Germany, Miocene, H = 2.06 (A) and 2.11 mm (B); IGS. C. Pupa suevica sensu Sandberger 1875, nomen nudum (= Gastrocopta sandbergeri sp. nov.) from Steinheim, Germany, Miocene, H = 2.05 mm; MNHN. D, E. Gastrocopta sandbergeri sp. nov. from Bełchatów, Miocene, H = 1.90 (D, Ml/1033/98b) and 2.14 (E, holotype, Ml/1033/98a); ISEA. F. Gastrocopta nouletiana (Dupuy, 1850) from Bełchatów, Miocene, Ml/1031/98, H = 2.23 mm; ISEA. G. Gastrocopta serotina Ložek, 1964 from Ctiněves−Hýkovina, Czech Republic, Early Pleistocene, ML/567/75, H = 2.00 mm; ISEA ex coll. Ložek. H. Gastrocopta theeli (Westerlund, 1877) from Northern Caucasus, Recent, H = 1.92 mm; IGS. I. Gastrocopta pseudotheeli Steklov, 1966 from Fars, Northern Caucasus, Miocene, 3842/50, H = 1.85 mm; IGS.