Danoceras oviforme, 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 : 60-62

Danoceras oviforme sp. nov.

urn:lsid:zoobank.org:act:8DCABC85-83A4-4DAA-9B32-91D58875FB3F

Fig. 24A, C

Diagnosis

Danoceras with compressed oval conch-cross section (CHI = 1.2); mature body chamber with maximum conch height near its base with height of ca 36 mm and height to length ratio of ca 0.9; maximum conch heigh near adoral end of mature phragmocone.

Etymology

Refers to the egg-like conch form of mature specimens.

Type material

Holotype

ESTONIA • Moe trench, Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-108 . Paratypes

ESTONIA • 1 spec.; Vormsi Island , Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 1745- 276 • 1 spec.; Piirsalu quarry; Adila Formation, Pirgu Regional Stage; TUG 80-510 • 1 spec.; Vormsi Island , Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-70 .

Description

The holotype ( Fig. 24A) is a fragment of a phragmocone and a mature body chamber with parts of the outer shell preserved. The outer shell is apparently smooth at the position of the body chamber. The conch height at the base of the body chamber is 36 mm and the conch width 30 mm (CHI = 1.2). The conch cross section is oval, narrower at the ventral side. The phragmocone grows at a length of 33 mm from a conch height of 24 mm to 36 mm (angle of expansion = 21°) and the septa are 4.5 mm distant where the conch height is 35 mm (RCL = 0.13). The sutures are nearly directly transverse, forming only a very shallow lateral lobe. The septal foramen is 2 mm in diameter and positioned 2 mm from the conch margin where the conch height is 24 mm (RSH = 0.08, RSP = 0.09).

More complete mature body chambers are preserved in specimens GIT 878-70, TUG 80-510, TUG 1745-276 where a body chamber length of 32 mm is reached (0.9 of the corresponding conch height at the base of the body chamber). The conch height and width of the mature body chamber decreases toward the peristome with a convex outlines in lateral view. Probably a slight widening occurs at the adoral most part, resulting in an amphora-like apertural shape.

The conch dimensions vary very little among the four specimens: TUG 80-510 having the largest conch height with 37 mm and no smaller mature conch heights than 36 mm.

Comparison

This species is most similar to Danoceras fusiforme Balashov 1959 , from the Rakvere Regional Stage of Estonia, which, however, has an even smaller mature size (maximum mature conch width = 19 mm). Diestoceras acuminatum Strand, 1934 , which has a similar conch height at the base of the mature body chamber, can easily be distinguished from the new species in having an angle of expansion of the phragmocone of 28° ( Strand 1934: 86).