Neridomus liasina ( Dunker, 1844 )

Monari, Stefano, Valentini, Mara & Conti, Maria Alessandra, 2011, Earliest Jurassic patellogastropod, vetigastropod, and neritimorph gastropods from Luxembourg with considerations on the Triassic-Jurassic faunal turnover, Acta Palaeontologica Polonica 56 (2), pp. 349-384 : 357-358

Neridomus liasina ( Dunker, 1844)

Fig. 6 .

1844 Neritina liasina sp. nov; Dunker 1844: 188.

1847 Neritina liasina Dunker ; Dunker 1847: 110–111, pl. 13: 13–16.

1855 Neritina hettangiensis sp. nov.; Terquem 1855: 262, pl. 15: 11.

1867 Neritina hettangiensis Terquem ; Moore 1867: 564, pl. 15: 25, 26.

1901 Neritina liasina Dunker ; Böhm 1901: 214–215, pl. 8: 3, 4.

1988 Neritoma (Neridomus) hettangiensis (Terquem) ; Meier and Meiers 1988: 27, pl. 3: 8a, b.

1992 Neritoma (Neridomus) liasina (Dunker) ; Szente 1992: 334, pl. 2: 14.

Material.—Ten specimens: MNHNL BR 362, MNHNL BR 446, MNHNL BR 693, MNHNL BR 696, MNHNL BR 701 (two specimens), MNHNL BR 702, MNHNL BR 772, MNHNL BR 877, MNHNL BR 882, Brouch, Upper Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ).

Dimensions.—See Table 2.

Description.—Globose, obliquely elongated shell composed of about four, quite strongly convex whorls. Inner wall of the shell dissolved. Spire clearly to moderately elevated, formed by evenly convex whorls with rounded ramp. Last whorl with downward asymmetrical, pendant profile, and with concave subsutural band. Suture moderately impressed, quite rapidly shifting downward during the growth. Base globose, anomphalous. Aperture semilunar to drop−shaped, with distinct, acute sutural corner. Peristome continuous on the parietal lip and strongly prosocline. Outer lip sharp and smoothly passing to the basal lip. Inner lip very short. Parietal lip long. A broad, thickened, smooth to slightly swollen callus covers the inner and parietal lips and extends greatly over the base. Outer rim doi:10.4202/app.2010.0098

of callus distinct, evenly and widely arched in its lower part, slightly sinuous in its upper part. Apertural rim of callus slightly wavy. Shell smooth. Growth lines prosocline, straight to slightly prosocyrt.

Remarks.—Distinctive characters are the obliquely elongated shell, the asymmetrical, pendant profile of the whorls, which is slightly concave on the subsutural band of the last whorl, and the suture that distinctly shifts downward during the adult growth. These features permit us to ascribe the material to Neridomus liasina ( Dunker, 1844) .

Neridomus hettangiensis ( Terquem, 1855) seemingly differs from N. liasina in having a more impressed suture resulting in a more turbiniform shape of the spire. However, Dunker (1847) described a rather high variability in N. liasina . A relatively high variability has been observed in the specimens from Luxembourg as well. This mainly concerns the height of the spire and the convexity of the whorls. Thus, there is a morphological continuity between N. liasina and N. hettangiensis and both the species probably represent synonyms.

Stratigraphic and geographic range.—Early Hettangian ( Psiloceras planorbis Zone ), Halberstadt (Saxony−Anhalt, Germany); Hettangian, Hettange−Grande (Lorraine, France); Late Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ), Brouch ( Luxembourg); Hettangian, Mecsek Mountains (southern Hungary); Late Hettangian to Early Sinemurian, Coimbra and Algarve (Lusitanian Basin, Portugal); earliest Sinemurian ( Coroniceras [ Arietites ] bucklandi Zone), Southerndown (South Wales, United Kingdom).

Figures

Fig. 6. Neritimorph gastropod Neridomus liasina (Dunker, 1844) from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A. MNHNL BR362, dorsal (A1), apertural (A2), subapertural (A3), and apical (A4) views. B. MNHNL BR701−1, dorsal (B1), and apical (B2) views. C. MNHNL BR701−2, dorsal (C1), apical (C2), apertural (C3), and subapertural (C4) views. D. MNHNL BR702, apertural (D1), dorsal (D2), and subapertural (D3) views.E. MNHNL BR882 showing the absence of the inner shell wall by dissolution. F. MNHNL BR877, dorsal (E1), lateral (E2), apical (E3), apertural (E4), and subapertural (E5) views.