Cyrtorizoceras hariense, Kröger, 2025

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 84-85

Cyrtorizoceras hariense sp. nov.

urn:lsid:zoobank.org:act:08D1598D-B9FB-4C73-B47A-C2C7371DE0A7

Fig. 32E–F

Diagnosis

Large Cyrtorizoceras with nearly circular conch cross section, reaching a mature size of more than 60 mm; phragmocone expands at an angle of 18°–20°; conch only weakly curved; conch surface nearly smooth.

Etymology

Refers to Hari Strait, which is the sea strait west of Saxby shore, the type locality.

Type material

Holotype

ESTONIA • Vormsi Island , Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 878- 71 .

Description

The holotype is a curved fragment of a phragmocone and a nearly complete body chamber. The conch surface is nearly smooth, ornamented with relatively coarse growth lines near the aperture. At the base of the body chamber, the conch cross section is circular or nearly so with a height of 48 mm. At the peristome, the width is 62 mm. The body chamber is 55 mm long, with a slightly curved growth axis, and in lateral view its dorsal and ventral margins have a concave and a convex curvature, respectively. The diameter of the body chamber increases continuously from its base toward the peristome. The phragmocone is 45 mm long and increases in diameter from 34 mm to 48 mm (angle of expansion = 18°). The sutures are directly transverse and 6 mm apart where the conch height is 45 mm (RCL = 0.13). The siphuncle is marginal or nearly so and expands into the chambers with a diameter of ca 5 mm where the chamber length is ca 6 mm (SCR = 0.83).

Remarks

This species of Cyrtorizoceras is unique in having large mature size in combination with a nearly circular conch cross section.

Figures

Fig. 32. Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A–B. Beloitoceras sinuososeptatum (Roemer, 1861). A. Specimen TUG 939-56, from Haapsalu holm, Pirgu Regional Stage, lateral view. B. Specimen TUG 1723-26, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage, lateral view. C. Beloitoceras cf. sinuososeptatum (Roemer, 1861), specimen GIT 878-231, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. D. Cyrtorizoceras sp. A., specimen GIT 878-260, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage, lateral view.E–F. Cyrtorizoceras hariense sp. nov., holotype GIT 878-71, from Saxby shore (N), Vormsi Island, Estonia, Vormsi Regional Stage. E. View of prosiphuncular side. F. Lateral view. Scale bar = 20 mm, same scale in all figures.