Hosholmoceras, 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 : 102-103

Genus Hosholmoceras gen. nov.

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Type species

Hosholmoceras ovalis gen. et sp. nov. from Hosholm shore, Vormsi Island, Estonia, Adila Formation, Pirgu Regional Stage.

Diagnosis

Endogastrically curved brevicones with very short chambers (RCL ca 0.05–0.07); conch cross section compressed or subtriangular; in lateral view mature conch slightly gibbous with largest conch heights near the base of the mature phragmocone; mature body chamber short, simple conical; sutures with shallow lateral lobes; siphuncle marginal, small; siphuncular segments rounded, expanded; septal necks cyrtochoanitic; endosiphuncular bulettes occur.

Etymology

Hosholm is the type locality of this genus.

Comparison

This genus is superficially similar to Hemibeloitoceras Balashov, 1962b , in having very short chambers (RCL ca 0.08) and a relatively thin, marginal siphuncle with simple expanded siphuncular segments. However, the conch of Hemibeloitoceras is exogastrically curved, expands gradually and is slenderer (angle of expansion ca 8°) while the sutures are directly transverse without a lateral lobe. Another curved breviconic form with very short chambers is Antiphragmoceras Foerste, 1925 . This also differs from Hosholmoceras gen. nov. in having an exogastrically curved conch.