Neridomus cannabis ( Terquem, 1855 )

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 : 359-360

Neridomus cannabis ( Terquem, 1855)

Fig. 7 .

1855 Neritina cannabis sp. nov.; Terquem 1855: 262, pl. 15: 12a, b.

?1855 Neritina arenacea sp. nov.; Terquem 1855: 263, pl. 15: 10a, b.

1867 Neritina canalis [sic] Terquem; Moore 1867: 564, pl. 15: 21, 22.

1902 Neritina cannabis Terquem ; Cossmann in Chartron and Cossmann 1902: 193–194, pl. 4: 18, 19.

1988 Neritoma (Neridomus) arenacea (Terquem) ; Meier and Meiers 1988: 27, pl. 2: 7a, b.

Material.— Five specimens: MNHNL BR 305, MNHNL BR 365, MNHNL BR 878, MNHNL BR 879, MNHNL BR 883, Brouch, Upper Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ).

Dimensions.—See Table 2.

Description.—Neritiform, globose shell consisting of four, strongly convex whorls. Inner wall of the shell dissolved. Spire moderately prominent. Whorls profile evenly convex in the juvenile and adult spire, slightly downward asymmetrical in the last whorl. Whorls provided with a convex ramp smoothly passing to the outer whorl face and becoming indistinct during the last growth. Suture slightly impressed and shifting downward only in the final half of the last whorl. Periphery well rounded and not exposed on the spire. Base globose and anomphalous. Aperture drop−shaped, with acute sutural corner. Peristome prosocline and continuous on the parietal lip. Outer lip evenly convex, increasing its convexity in the basal part. Parietal region strengthened by a strong and broad callus covering the axial depression of the base where it can form a slightly swollen pad. Outer rim of callus distinct, forming a semicircular line around the axial region of the base. Apertural rim of callus sharp, slightly concave along the middle part of parietal lip. Shell smooth. Growth lines prosocline, almost straight on the spire, feebly prosocyrt on the base.

Remarks.—The smallest specimens ( MNHNL BR 305, MNHNL BR 365) correspond to the original description and illustration of Neridomus cannabis ( Terquem, 1855) , a species erected by Terquem (1855) based on shells with a size of few millimetres. However, some of the largest specimens tend to resemble Neridomus arenacea ( Terquem, 1855) . One cannot exclude that a detailed study of more material would doi:10.4202/app.2010.0098

reveal that N. arenacea represents the fully adult stage of N. cannabis .

Neridomus cannabis clearly differs from Neridomus liasina ( Dunker, 1844) in its smaller size, a more globose shape of the shell, and more evenly convex whorls. Moreover, in N. cannabis the suture is more impressed and it shifts downward only during the last growth stage.

The specimen ascribed by Bourrouilh (1966: 34, fig. 6) to N. cannabis , from the Early Sinemurian ( Caenisites turneri Zone to Asteroceras obtusum Zone ) of Rosfet−er−Rjem (Eastern High Atlas, Morocco) ( Bourrouilh 1966; Dresnay 1966) has a much more depressed spire, and the whorls lack a ramp. This assignment to Terquem’s (1855) species is highly questionable.

Stratigraphic and geographic range.—Hettangian, Hettange−Grande (Lorraine, France); Late Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ), Brouch ( Luxembourg); Hettangian, Le Simon−la−Vineuse (Vendée, France); earliest Sinemurian ( Coroniceras [ Arietites ] bucklandi Zone), Brocastle (South Wales, United Kingdom).

Figures

Fig. 7. Neritimorph gastropod Neridomus cannabis (Terquem, 1855) from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A. MNHNL BR365, dorsal (A1), apical (A2), apertural (A3), and subapertural (A4) views. B. MNHNL BR878, apertural (B1), lateral (B2), apical (B3), and dorsal (B4) views. C. MNHNL BR879, apertural (C1), dorsal (C2), and apical (C3) views. D. MNHNL BR883, subaxial section showing the absence of the inner shell wall by dissolution.