Beloitoceras uuemoisense, 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 : 83

Beloitoceras uuemoisense sp. nov.

urn:lsid:zoobank.org:act:F793DBD7-51A6-4A8B-8939-F9372673A510

Fig. 28G–H

Diagnosis

Beloitoceras with a maximum conch height of ca 18 mm near mid-length of mature body chamber; compressed conch cross section with CHI of ca 1.35; angle of expansion of the phragmocone ca 20°, in lateral view ventral conch margin convex and dorsal conch margin concave throughout entire length; body chamber with constriction near mature peristome.

Etymology

Referring to the type locality.

Type material

Holotype

ESTONIA • Läänemaa, Uuemõisa; Adila Formation, Pirgu Regional Stage ; TUG 1745-290 .

Description

The holotype is a nearly complete conch of a small mature curved brevicone ( Fig. 28G–H ). Its greatest conch height of 17.5 mm occurs slightly adoral of the base of its body chamber, where the conch width is 13 mm (CHI = 1.35). At the base of the body chamber, the conch height is 17 mm and the corresponding width 12 mm (CHI = 1.42). The conch cross section is elliptical with nearly equally narrowly rounded dorsal and ventral margins. The body chamber is nearly straight, in lateral view its prosiphuncular margin is more curved (convex) than the antisiphuncular margin (concave). The conch height decreases toward the aperture with a marked constriction ca 2 mm from the peristome forming an amphora like apertural opening. The peristome appears to be straight transverse. The phragmocone is curved and increases in height from 11 mm to 17 mm at a length of 16 mm (angle of expansion = 21°). The sutures form wide lateral lobes, they are ca 2 mm apart where the conch height is 17 mm (RCL = 0.12). Details of the siphuncle are not known.

Comparison

This is a small species of Beloitoceras , superficially similar to species of Oncoceras . It differs from species of Oncoceras in having a gibbous mature body chamber and in lacking the convex portion of the conch margin at the antisiphuncular conch margin. The genus Beloitoceras is species rich, palaeogeographically widespread and stratigraphically relatively long ranging. Flower (1946) distinguished several groups within the genus. Beloitoceras uuemoisense sp. nov. can be placed in Flower’s (1946) group III of B. pandion Flower, 1946 , which comprises faintly gibbous species with a concave conch margin at the antisiphuncular side. Within this group, B. uuemoisense is unique because of its small adult size of less than 20 mm.

Figures

Fig. 28. Graciloceratidae Flower, 1950 and Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A–D. Hiiumoceras hiiuense gen et sp. nov., paratype GIT 426-421, from Paluküla, Hiimuaa Island, Vormsi Regional Stage. A. Lateral view. B. View of antisiphuncular side. C. View of prosiphuncular side. D. Adapical view. E. Rizosceras teres sp. nov., holotype TUG 1745-188, from Saaremõisa (Lyckholm), Vormsi Regional Stage, view of prosiphuncular side with details of siphuncle visible. F, I–J. Beloitoceras (?) sp., specimen GIT 426-1081, from Pirgu river outcrops, Raplamaa, Pirgu Regional Stage. F. Lateral view. G–H. Beloitoceras uuemoisense sp. nov., holotype GIT 1745-290, from Uuemõisa, Läänemaa, Pirgu Regional Stage. G. Lateral view. H. View of antisiphuncular side. I. View of prosiphuncular side. J. Adapical view. K–L. Multiceratoidea gen. et sp. indet. C, specimen GIT 878- 234, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. K. Adapical view. L. Lateral view. Scale bar = 10 mm in all figures except E, same scale in A–D, and in F–K. Scale bar in E = 5 mm.