Eustoma gracilis Gründel & Nützel, 2024, sp. nov.
Creators: name: Gründel, Joachim
name: Nützel, Alexander
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Eustomatidae
Eustoma
Eustoma gracilis

description: Eustoma? gracilis sp. nov.
Plate 8: figs 15–17
Etymology.
Latin gracilis – slender; because of the slender shell shape.
Holotype.
SNSB-BSPG 2016 XXI 1804.
Paratypes.
4 specimens, SNSB-BSPG 2016 XXI 1805 –1807.
Type locality and stratum.
Upper Jurassic (Kimmeridgian) reefal limestones from the locality Saal near Kelheim, Lower Bavaria (Gründel et al. 2015, 2022).
Diagnosis.
Shell moderately high-spired, relatively large and slender; whorls increase evenly in width; whorl face without distinct spiral cords; subsutural nodes become particularly large on the last whorls; transition from whorl face to base evenly rounded, with nodular spiral cord; base covered with nodose spiral cords, increasingly weaker towards center of base; nodes connected by bulbous, opisthocline axial ribs.
Description.
Shell moderately high-spired, slender, with acute apex; large specimen 45 mm high; early whorls poorly preserved, with straight whorl face; late whorls with subsutural row of large rounded, axially elongated nodes (9–10 per whorl), giving spire gradate appearance by forming narrow ramp; subsutural nodes extending over more than half of whorl face height; suprasutural spiral cord with weaker and more numerous nodes; transition from whorl face to convex base evenly rounded; base with knobby spiral cords; spiral cords on base becoming weaker towards center of base while nodes on them become smaller; nodes connected by bulbous opisthocline axial ribs; whorls probably also with fine spiral lirae (obscured by poor preservation); base apparently with narrow umbilicus; aperture not preserved.
Remarks.
Ditretus sp., cf. rostellaria (Buvignier) sensu Gründel et al. (2019) is smaller, the strong abapical spiral cord lies directly at the suture and has larger tubercles, on the base a third, clearer and tuberculated spiral cord is formed, the spiral cords on the base are more numerous and are not nodular, the flanks are covered with weak spiral cords. Cerithium rostellaria Buvignier, 1852 has smaller subsutural nodes, the whorls are angulated by the nodes, and axial ribs are missing on the base. Cerithium schardti Loriol in Loriol and Koby (1895) has smaller and barely abapically elongated nodes; it lacks a knobby spiral cord at the transition from whorl face to base and axial ribs on the base. Cerithium kelheimense Schlosser, 1882 is smaller and the shell is covered with weak spiral cords and it lacks a knobby spiral cord at the transition from whorl face to base. Ditretus nodosostriatus Peters sensu Yin (1931) has smaller and more numerous subsutural nodes, 1–2 spiral cords above the abapical suture; its base is unknown. Ditretus thurmanni Loriol sensu Yin (1931) is smaller, the nodes form only an indistinct ramp; it has 1–2 spiral ribs with small nodes between the upper row of nodes and the abapical suture. Nerinea orbignyana Zeuschner, 1850 has a series of small nodes above the abapical suture, the base is almost flat and lacks sculpture.
description: Published as part of Gründel, Joachim & Nützel, Alexander, 2024, Late Jurassic (Upper Kimmeridgian) gastropods from Saal near Kelheim (Germany, Bavaria), pp. 19-72 in Zitteliana 98 on pages 19-72, DOI: 10.3897/zitteliana.98.e138605