Cyclonema Hall, 1852

Ferrari, Mariel, Bertero, Verónica & Carrera, Marcelo G., 2024, Late Ordovician (Sandbian-Hirnantian) marine gastropods from the Argentine Precordillera: their biogeographical significance in a middle to high latitudinal setting, Acta Palaeontologica Polonica 69 (4), pp. 747-767 : 759

Genus Cyclonema Hall, 1852

Type species: Pleurotomaria bilix Conrad, 1842 , by original designation; from the lower Silurian of North America .

Remarks.— Knight et al. (1960) characterized members of Cyclonema as turbiniform to trochiform shells, with sharp spiral ribs and fine collabral threads. The diagnosis proposed by Thompson (1970) also characterized Cyclomena species as anomphalous shells, with an polygonal to auriform aperture, columellar lip lunate and excavates, ornament consisting on three orders of spiral lines cancellated by collabral lirae commonly thicken into growth wrinkles.

Stratigraphic and geographic range.—Middle Ordovician– Silurian; North America, South America, Europe.

Cyclonema cf. bilix ( Conrad, 1842) Fig. 3O–Q .

2020 Cyclonema bilix ( Conrad, 1842) ; Bertero 2020: 69, pl. 8: 8–11.

Material.— CEGH-UNC 24765–24770, six recrystallized teleoconchs; from the Sandbian, Upper Ordovician, La Pola Formation, Quebrada La Pola (Level LP 1), Sierra de Villicum and Quebrada de Don Braulio, San Juan Province, Argentina.

Description.—Turbiniform to trochiform, medium-sized shell with a height of 15 mm and a width of 10–18 mm; pleural angle of 55−85º. Teleoconch consists of four whorls in the best preserved specimen ( Fig. 3O 1 ). The ramp of whorls is flattened to slightly concave and excavated; the periphery of whorls is strongly convex. Sutures are impressed in a spiral channel. The ornament consists of three orders of regularly spaced spiral lirae. The spiral lirae are intercepted by fine and acute prosocline growth lines forming a reticulate pattern with small and rounded nodes at the intersection points ( Fig. 3O 2 ). The base is flattened to slightly convex and the aperture is not completely visible; the inner lip probably concave.

Remarks.—The species herein described from the Upper Ordovician of Argentina strongly resembles Cyclonema bilix ( Conrad, 1842) from the Katian, Upper Ordovician of North America. According to Thompson (1970) C. bilix has a trochiform to conical shell with straight to concave whorl profile and rounded periphery, and is characterized by the presence of three orders of spiral ribs which form a reticulate pattern with strongly prosocline collabral lirae; these features are clearly visible in the material from the Argentine Precordillera. Cyclonema cf. bilix , however, has less conical and more convex whorl profile, the typical polygonal to rounded aperture, the straight to concave inner lip and the outer lip reflected obliquely on adults is not completely visible in our material and, thus, it is tentatively assigned to the species. Cyclonema humerosum Ulrich & Scofield, 1897 (in Thompson 1970: 244, pl. 32: 10–13), from the Katian, Upper Ordovician of North America, differs from C. cf. bilix in having a more deeply channeled suture, a broader and horizontal ramp, a more angular periphery and stronger and more acute spiral lirae. Cyclonema inflatum Ulrich & Scofield, 1897 (in Thompson 1970: 245, pl. 32: 14–18), also from the Katian, Upper Ordovician of North America, has a more slender and higher spire than the Argentinean form, a more globose last whorl, and the ornament consists in two orders of acute spiral cords more separated on the upper part of the whorl. Cyclonema ( C.) hiiumaa Teichert, 1928 (in Isakar 1995: 185, figs. 1–6), from the Silurian of Estonia, has a broadly D-shaped aperture with the inner lip thickened and reflected.

Figures

Fig. 3. Sandbian–Hirnantian (Late Ordovician) gastropods from La Pola and Don Braulio formations at the Sierra Villicum and Quebrada Don Braulio localities, Argentine Precordillera.A, B. Tropidodiscid bellerophontoid Tropidodiscus sp. A. CEGH-UNC 24679-5 in transversal view. B. CEGH-UNC 24678 in lateral view.C. Trochonematoid Trochonemella? sp., CEGH-UNC 24752, in lateral and apertural (C1), apical and lateral (C2), and lateral (C3, C4) views. D−G. Raphistomatid Scalites peracutum (Ulrich & Scofield 1897). D. CEGH-UNC 24772, in lateral view. E. CEGH-UNC 24783, in apical view. F. CEGH-UNC 24773, in apical view. G. CEGH-UNC 24786-9, in basal and umbilical views. H, I. Holopeid vetigastropod Holopea sp. H. CEGH-UNC 25451, associated specimens in lateral view. I. CEGH-UNC 25448, in lateral view. J−N. Eotomariid Clathrospira gondwanica sp. nov. J. CEGH-UNC 24737, paratype, in lateral view. K. CEGH-UNC 24738-11, holotype, in lateral view (K1, K2). L. CEGH-UNC 24740, in apical (L1) and lateral (L2) views. M. CEGH-UNC 24738-11, holotype, in lateral (M1) and basal (M2) views. N. CEGH-UNC 24739, in apical (N1) and basal and apertural (N2) views. O–Q. Platyceratid Cyclonema cf. bilix (Conrad, 1842). O. CEGH-UNC 24765, in apical view (O1), ornament detail (O2). P. CEGH-UNC 24766-1, in lateral views (P1, P2). Q. CEGH-UNC 24767-2, in lateral view.

Fig. 1. Geographical, stratigraphical and biostratigraphical setting of the Argentine Precordillera during the Late Ordovician. A. Map showing location of the study area in the San Juan Province,Argentina. B, C. Geological maps of the study area including the outcrops of Upper Ordovician marine deposits of the Don Braulio and La Pola formations. D. Stratigraphic column of the La Pola and Don Braulio formations at Sierra Villicum, and detail of sampled interval showing the gastropod fauna associations described in the text. E. Biostratigraphical scheme of La Pola and Don Braulio formations based on conodonts and graptolites.

Fig.2.Sandbian–Hirnantian (LateOrdovician) gastropods from La Pola and Don Braulio formations at the Sierra Villicum locality,Argentine Precordillera. A, B. Bucanopsin bellerophontoid Sphenosphaera sp. A. CEGH-UNC 24795-2, in lateral (A1), dorsal (A2, A3), and apical (A4, A5) views. B. CEGH- UNC 24796-6, in ventral view. C. Bucaniin bellerophontoid Bucania sp., CEGH-UNC 24733-1, in lateral (C1) and dorsal (C2) views. D. Plectonotin bellerophontoid Tetranota argentina sp. nov., CEGH-UNC 24713, holotype, in dorsal (D1, D5, D6) and dorsal-lateral (D2, D3) views, cross section (D4) and ornament detail (D7). E−G. Sinuitin bellerophontoid Sinuites aff. S. reticulatus Perner, 1903. E. CEGH-UNC 24694-1, in apertural and basal view. F. CEGH-UNC 24696, in basal and apertural (F1) and lateral (F2−F4) views. G. CEGH-UNC 24697-3, in dorsal-lateral view (G1, G2) and ornament detail (G3, G4). H. CEGH-UNC 24694, in lateral view.