Trochotoma vetusta 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 : 372-374

Trochotoma vetusta Terquem, 1855

Fig. 15 .

1855 Trochotoma vetusta sp. nov.; Terquem 1855: 267–268, pl. 16: 10.

1867 Trochotoma brocastellensis sp. nov.; Moore 1867: 552, pl. 15: 29.

1934 Ditremaria (Ditremaria) vetusta (Terquem) ; Haber 1934: 366.

1966 Trochotoma meneghinii Gemmellaro ; Bourrouilh 1966: 43–44, fig. 17.

1988 Trochotoma vetusta Terquem ; Meier and Meiers 1988: 34, pl. 8: 17a–c.

2002 Trochotoma (Trochotoma) vetusta Terquem ; Fischer et al. 2002: 444, fig. 3−1a, b.

Material.— Thirty−three specimens: MNHNL BR 221−2, MNHNL BR 320, MNHNL BR 361, MNHNL BR 375−2, MNHNL BR 378, MNHNL BR 418−2, MNHNL BR 454, MNHNL BR 455−2, MNHNL BR 458, MNHNL BR 460, MNHNL BR 461, MNHNL BR 465, MNHNL BR 466, MNHNL BR 469, MNHNL BR 473−1, MNHNL BR 533, MNHNL BR 667, MNHNL BR 678, MNHNL BR 679, MNHNL BR 680, MNHNL BR 685, MNHNL BR 698 (two specimens), MNHNL BR 704, MNHNL BR 705, MNHNL BR 706, MNHNL BR 708, MNHNL BR 710, MNHNL BR 713, MNHNL BR 754, MNHNL HE123 , MNHNL HE133 (two specimens), Brouch, Upper Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ) .

Dimensions.—See Table 2.

Description.—Trochiform, gradate shell composed of about six teleoconch whorls. Juvenile spire feebly cyrtoconical, adult spire coeloconical. Ramp narrow and convex, becomes increasingly pronuncied during growth. Outer whorl face flat to moderately convex, markedly wider than the ramp, oblique and forming an obtuse angulation with the ramp. Periphery marked by a spiral bulge on the juvenile and adult whorls. The peripheral bulge tends to vanish during growth of the last whorls where it becomes a rounded angulation. Suture moderately impressed, running in the middle of the peripheral carina and shifting slightly below it on the last whorl. Selenizone convex, placed on the angulation of the whorl surface. An exhalant hole (trema), seemingly elliptical and strongly elongate in spiral direction, forms before the last peristome. Selenizone reduced to a shell seam between the exhalant hole and the outer lip. Final part of the last whorl expanded. Base with well rounded surface and a broad, funnel−like umbilicus. Aperture elliptical, well−elongated in abaxial direction. Peristome strongly prosocline, discontinuous on the parietal lip. Inner lip strongly oblique, elongated within the umbilical cavity, almost straight and forming an obtuse, rounded angulation at the junction with the basal lip. Ornament consists of dense, distinct and unevenly sized spiral threads covering the whole surface of the whorls and are separated by narrower interspaces. The ramp can be crossed by feeble collabral striae. Base ornamented with spiral threads which are thinner and more widely spaced than those of the spire. Selenizone hidden by the spiral ornament, coinciding with a duplicated spiral thread which is wider than the others. Growth striae strongly prosocline and evenly prosocyrt on the spire, opisthocyrt on the base.

Remarks.—The species is rather variable in spire height, ramp, and outer whorl face inclinations, as well as in the prominence of the peripheral carina and of the ornament. Owing to that variability, and to the general shape of the shell, Trochotoma brocastellensis Moore, 1867 is here included in the synonymy of Trochotoma vetusta Terquem, 1855 .

Trochotoma meneghinii Gemmellaro, 1879 (Gemmellaro 1879: 367, pl. 28: 11, 12) differs from T. vetusta in having a more acute spire and a conical shape of the shell owing to a doi:10.4202/app.2010.0098

narrower ramp. Moreover, in T. meneghinii the periphery is smoothly angulated whereas in T. vetusta it is marked by a slightly bulge−shaped carina. In agreement with Fischer et al. (2002: 444), the specimen described by Bourrouilh (1966) as T. meneghinii should be referred to T. vetusta .

Stratigraphic and geographic range.—Hettangian, Hettange−Grande (Lorraine, France); Late Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ), Brouch ( Luxembourg); earliest Sinemurian ( Coroniceras [ Arietites ] bucklandi Zone), Brocastle (South Wales, United Kingdom); Early Sinemurian, central Apennines ( Italy); Late Sinemurian ( Echioceras raricostatum Zone ) to earliest Carixian, Eastern High Atlas ( Morocco).

Figures

Fig. 15. Trochotomid gastropod Trochotoma vetusta Terquem, 1855 from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A. MNHNL BR704, dorsal (A1), apical (A2), lateral (A3), and apertural (A4) views. B. MNHNL BR754, dorsal (B1), apical (B2), subapertural (B3) views, and detail of the exhalant hole and of the shell seam (B4). C. – MNHNL BR710, apical (C1), dorsal (C2), basal (C3), and apertural (C4) views. D. MNHNL BR361, apertural (D1), basal (D2), dorsal (D3), apical (D4), and lateral (D5) views. E. MNHNL BR705, dorsal (E1) and apical (E2) views, and detail of the exhalant hole and of the shell seam (E3). The arrow indicates the position of the selenizone.