D, E. Gastrocopta sandbergeri from Bełchatów, Miocene, H = 1.90 (D, Ml/1033/98b) and 2.14 (E, holotype, Ml/1033/98a); ISEA

Diagnoza

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.

Porównanie

    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.

Autekologia

terrestial

Występowanie geograficzne

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.

Zasięg czasowy

Lower/Mid Miocene

Materiały muzealne

Holotype: ISEA Ml/1033/98a and 19 paratypes ISEA Ml/1033/98b. (Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Cracow, Poland)

Literatura

Stworzewicz, E. and  Prisyazhnyuk, V. A. 2006. A new species of Miocene terrestrial gastropod Gastrocopta from Poland and the validity of 'Pupa (Vertigo) suevica'. Acta Palaeontologica Polonica 51 (1), 2006: 165-170.