Anodomaria schroederi, Monari & Valentini & Conti, 2011

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 : 367-368

Anodomaria schroederi sp. nov.

Fig. 12A, B.

v1988 Trochotoma maubertense Terquem and Piette ; Meier and Meiers 1988: 33, pl. 7: 16a, b.

Etymology: The species is dedicated to Maggy Schroeder, a passionate collector of fossils who greatly contributed to enrich the palaeontological collections of the MNHNL.

Type material: Holotype: specimen MNHNL BR 342 ( Fig. 12A ) . Paratypes: one specimen, MNHNL BR 871.

Type locality: Brouch (Mersch, Grand−Duchy of Luxembourg) .

Type horizon: Luxembourg Sandstone Formation, Upper Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ).

Dimensions.—See Table 2.

Diagnosis.—Shell distinctly gradate. Juvenile spire depressed. Early whorls provided with a relatively wide, convex ramp having the outer edge marked by a rounded angulation. Ornamentation roughly reticulate by intersection of evenly sized and spaced spiral threads with irregularly sized and dense collabral threads. Ramp sculptured with relatively strong, evenly distributed collabral riblets which fade out at the outer edge of the ramp. They tend to fade out during the last growth as well.

Description.—Trochiform, distinctly gradate shell consisting of about six whorls. Juvenile spire low. Early whorls well−rounded and separated by an impressed suture. Adult whorls angulated and with trapezoidal cross−section. Ramp slightly convex and weakly inclined. It enlarges and increases its inclination during the growth. Outer whorl face straight in juvenile whorls, slightly concave in adult whorls. Selenizone relatively wide, running slightly above the middle of the outer whorl face, weakly concave on the early doi:10.4202/app.2010.0098

whorls and becoming slightly convex on the last whorls. Periphery smoothly angulated, slightly prominent and swollen. Base relatively flat with feebly convex surface, and widely umbilicated. Aperture not preserved. Ornament composed of a network of spiral threads and collabral riblets and threads. Ramp ornamented with four to five, equally spaced and sized spiral threads intersected by marked, prosocline, and evenly spaced collabral riblets. Collabral riblets fading out at the edge of the ramp, intercalated to fine, irregularly sized and dense collabral threads. Other face with few spiral threads above and below the selenizone. These form a network with densely distributed collabral threads and bear small granulation at the intersection points. Angulation of the whorl surface and peripheral angulation marked by a spiral thread which is wider than the others. Selenizone with upper and lower rims marked by a fine spiral thread. Lunulae rather well defined. They are well spaced in the juvenile whorls and become thinner, densely spaced and unevenly sized on the adult spire. Base ornamented with regularly sized, somewhat densely spaced spiral threads roughed by intersection with growth threads. Growth lines moderately prosocline and prosocyrt on the ramp and above the selenizone, orthocline to slightly opisthocline and prosocyrt below the selenizone and on the peripheral band of the base. They are opisthocyrt on the base and become slightly prosocyrt on the periumbilical area.

Remarks.—This species belongs to the genus Anodomaria Szabó, 1980 as is indicated by the presence of an angulation of the whorl lacking nodes, a moderately wide, flat to concave selenizone running on the outer face of the whorls, a wide umbilicus, a slightly bulged peribasal angulation, and a reticulate ornament.

Meier and Meiers (1988) referred the material described here to Trochotoma maubertense Terquem and Piette, 1865 ( Terquem and Piette 1865: 55, pl. 4: 20, 21). However, the species of the genus Trochotoma Eudes−Deslongchamps, 1843 are characterised by an exhalant hole and selenizone on the angulation of the whorls, and a funnel−like umbilicus. In contrast, in Anodomaria schroederi sp. nov., like in the other relatives, the exhalant hole is absent and the selenizone is located on the outer face of the whorls. Moreover, the umbilicus, although relatively wide, is not funnel−shaped.

Anodomaria schroederi is the oldest representative of the genus Anodomaria , a taxon previously known as ranging from the Late Sinemurian to Pliensbachian ( Szabó 2009). It differs from the type species, Anodomaria scacchii ( Gemmellaro, 1874) ( Gemmellaro 1874: 92, pl. 12: 18; Szabó 1980: 58, pl. 2: 6, 7; Conti et al. 2007: pl. 12: 18; Szabó 2009: 37, fig. 31), and from Anodomaria stojaspali Szabó, 2008 ( Szabó 2008: 171, fig. 3; 2009: 36, fig. 29), in the more gradate spire owing to a wider ramp, and in the presence of distinct collabral ribs on the ramp.

Stratigraphic and geographic range.—Late Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ), Brouch ( Luxembourg).

Figures

Fig. 12. Pleurotomariid and ptychomphalid gastropods from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A, B. Anodomaria schroederi sp.nov. A – Holotype, MNHNL BR342, dorsal (A1) and apical (A2) views. B – Paratype, MNHNL BR871, dorsal (B1), lateral (B2), and apical (B3) views. C. Ptychomphalus rotellaeformis (Dunker, 1847), MNHNL BR364, apertural (C1), dorsal (C2), basal (C3), apical (C4), and lateral (C5) views.