Gorbormoceras vohilaidense Kröger 2025
Creators: name: Kröger, Björn
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Actinoceratida
Uranoceratidae
Gorbormoceras
Gorbormoceras vohilaidense

description: Gorbormoceras vohilaidense gen. et. sp. nov.
urn:lsid:zoobank.org:act: 820DB1BC-79F4-40A5-A0B0-19D08C785DD6
Figs 7B, 8F
Diagnosis
Same as for genus, by monotypy.
Etymology
The name refers to Vohilaid Island, the type locality.
Type material
Holotype
ESTONIA • Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-235.
Description
The specimen is a slightly exogastrically curved mold of parts of a phragmocone and a body chamber. The conch cross section is apparently circular. At a conch diameter of 28–38 mm, the angle of expansion is 14°. At the base of the body chamber, the diameter is 31 mm. The preserved length of the body chamber is 60 mm. Although the outer shell is not preserved, traces of a relatively strong ornamentation with ca 20 longitudinal lirae around the circumference and a weak annulation are visible (Fig. 7B). Near the base of the body chamber, ca five annulations occur in a distance equal to the corresponding conch cross section.
The sutures form shallow lateral lobes and are slightly adorally shifted on the prosiphuncular side of the conch, the most adoral sutures are slightly crowded (chamber length 4.5 mm), at a conch height of 28 mm they are 6 mm distant (RCL = 0.21). The siphuncle is eccentrically positioned; near the apical end of the specimen, where the conch diameter is 31 mm, it is 10 mm distant from the conch margin and has a diameter of ca 3.3 mm (RSP = 0.36). The septal necks are short recumbent or achoanitic. The connecting ring is thin, and forms widely expanded segments with adnate areas at the adoral and apical septal surfaces (Fig. 8F). Where the septal foramen is 3.3 mm, and the chamber length is 4 mm, the segments expand toward a height of 8.6 mm (RSS = 2.15).
Remarks
This specimen is externally similar to Cycloceras fenestratum Eichwald, 1860 with regard to the general conch shape and its traces of the ornamentation (ca 20 longitudinal lirae and ca five annulations per distance equal to the corresponding conch cross section). However, it is larger (maximum diameter ca 25 mm in C. fenestratum) and has a larger angle of expansion (angle of expansion <10° in C. fenestratum) (see e.g., Kröger 2013). Internally, the specimen is similar to species of Ormoceras.
Comparison
The widely expanded siphuncle and the ornamentation of the new species are most similar to Troedssonoceras (?) obscuriliratum Flower, 1946, from which it differs in having a more centrally positioned siphuncle and a weakly annulated conch. Another orthoconic species with a nodular ornamentation, comparable to G. vohilaidense sp. nov., is Spyroceras (?) nodosum Sweet & Miller, 1957, from which the internal characters are not known.
description: Published as part of Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, pp. 1-169 in European Journal of Taxonomy 978 on pages 22-23, DOI: 10.5852/ejt.2025.978.2801, http://zenodo.org/record/14988376