Gorbormoceras, 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 : 21-22

Genus Gorbormoceras gen. nov.

urn:lsid:zoobank.org:act:923963A2-FF6F-4A62-8421-E6B8E2B10E76

Type species

Gorbormoceras vohilaidense gen. et. sp. nov., from Vohilaid shore (E), Vohilaid Island, Estonia; Adila Formation, Pirgu Regional Stage.

Diagnosis

Slightly exogastrically curved, nearly orthoconic longicones with a circular (or nearly so) conch cross section; ornamented with shallow annulation and distinct longitudinal lirae; sutures form shallow lateral lobes; ca five chambers occur at a length equal to corresponding conch cross section; siphuncle slightly eccentrically positioned; septal necks short or absent; siphuncular segments widely expanded with adnate areas at adoral and apical surfaces of septa; endosiphuncular and cameral deposits not known.

Etymology

Combination of the two genus names Gorbyoceras and Ormoceras , because the new genus, in a unique fashion, combines essential features of both genera.

Remarks

The new genus is provisionally assigned to the Ormoceratidae because of its subcentrally positioned, widely expanded siphuncle, and the very short recumbent or absent septal necks. Short or very short cyrtochoantitic to recumbent septal necks and widely expanded siphuncular segments are known from other ormoceratids, such as Ormoceras and Orthonybyoceras Shimizu & Obata, 1935 .

Comparison

Troedssonoceras Foerste, 1928b is similar in having widely expanded siphuncular segments and a longitudinal ornamentation. In Troedssonoceras , the siphuncular shape is similar to Deiroceras (with cyrtochoanitic septal necks), and the connecting ring is not adnate (see, e.g., Flower 1946: 535). Eskimoceras Troedsson, 1926 has an annulated conch and widely expanded siphuncular segments. It differs from the new genus in having cyrtochoanitic septal necks and in lacking a longitudinal ornamentation.