Kiaeroceras ormsoense Kröger, 2025, sp. nov.
Creators: name: Kröger, Björn
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Cyrtogomphoceratidae
Kiaeroceras
Kiaeroceras ormsoense

description: Kiaeroceras (?) ormsoense sp. nov.
urn:lsid:zoobank.org:act: DF10785E-0267-4AD5-B8E6-90B2BBD9EA1F
Figs 35F, H, 37D
Diagnosis
Kiaeroceras with CHI of ca one, and an adult body chamber with a height of ca 50 mm, which is nearly as long as high.
Type material
Holotype
ESTONIA • Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 878- 63.
Description
The holotype is a fragment of the phragmocone and a mature body chamber (Fig. 35F, H). Parts of the outer shell are preserved, which show that the shell was apparently smooth or was ornamented with fine irregularly spaced growth lines. At the base of the body chamber, the conch height is 52 mm and the CHI nearly 1. In cross section, the margin on the prosiphuncular side is narrower than the opposite margin. The body chamber is 52 mm long and at the aperture 54 mm in diameter. The peristome is only partially preserved and where visible is simple and directly transverse. In lateral view, the body chamber is straight with straight or very slightly convex dorsal and ventral conch margins. The phragmocone is slightly curved endogastrically. The sutures are directly transverse and straight. The adoral-most sutures are crowded, indicate maturity of the specimen. At a conch height of 42 mm, the phragmocone is 39 mm wide (CHI = 1.07), and 30 mm further adorally, the height is 31 mm (angle of expansion = 21°). The septa are 4 mm apart where the conch height is 40 mm (RCL = 0.1). The siphuncle is strongly expanded within the chamber in lateral view, wider near the adapical surface of the septa with a maximum height of 8 mm where the septal foramen is 6 mm the chamber length is 4 mm, and the conch height is 40 mm (RSH = 0.15, RSS = 1.33, SCR = 2). There, the distance of the septal foramen from the conch margin is 2 mm. The connecting ring is thick and thick endosiphuncular bulletes occur. The septal necks are cyrtochoanitic (Fig. 37D).
Remarks
This specimen is placed with question mark into Kiaeroceras because it differs from other members of the genus in having a circular conch cross section, a wider angle of expansion, resulting also in a slightly bulged mature body chamber, and it is slightly endogastrically curved. Its gross morphology is intermediary between typical members of Diestoceras and Kiaeroceras. It differs from the former in having a slender shell and a relatively elongate body chamber. The erection of a new genus for this species must wait until more material is known, especially from the apical parts of Kiaeroceras, which is mostly known from isolated mature body chambers. Herein, this species is placed within Kiaeroceras because it fits the existing (relatively broadly defined) diagnosis of this genus (see above).
The siphuncular structure, and in particular the actinosiphonate deposits of Diestoceras are poorly known. Flower & Teichert (1957: 42) discuss the possibility that the actinosiphonate deposits seen in some species of the genus are modified bullettes, which would mean that it should be transferred to the Discosorida. This species, being intermediate between Kiaeroceras and Diestoceras could support this hypothesis.
Comparison
The species is unique to the genus in having a CHI of nearly one and a slightly inflated mature body chamber.
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 108-109, DOI: 10.5852/ejt.2025.978.2801, http://zenodo.org/record/14988376