Ormoceras heckeri Teichert, 1930

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 : 20-21

Ormoceras heckeri Teichert, 1930

Fig. 8E

Ormoceras heckeri Teichert, 1930: 290 , pl. 7 fig. 21.

Ormoceras heckeri – Balashov 1953a: 211. ― Stumbur 1956: 176. ― Flower 1957: 11.

Diagnosis

Straight shell with circular cross section; siphuncular position subcentral, siphuncular segments barrel-shaped, approximately as high as long (SCR ca 1); septal necks very short and adnate to adoral surface of septa ( Nybyoceras -like).

Material examined

ESTONIA • 2 specs; Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-280 , TUG 1745-281 • 1 spec.; Vormsi Island , Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1680-19 .

Type locality and horizon

Niibi, Estonia; Adila Formation, Pirgu Regional Stage.

Description

Specimen TUG 1680-19 (Fig. 8E) is a short fragment of the phragmocone without external characters preserved, with circular conch cross section and a diameter of 36 mm, the septa are ca 7 mm apart (RCL = 0.19), and the siphuncle is eccentrically positioned (RSP = 0.34). The septal necks are short adnate and the connecting ring forms barrel-shaped segments with a height of 8 mm (SCR = 1.14).

Specimen TUG 1745-281 is a fragment of a phragmocone 28 mm long, and increasing in diameter 20–23.5 mm (angle of expansion = 7°). The conch surface is not preserved. The sutures are directly transverse and straight with an RCL of 0.26. The septal foramen is nearly centrally positioned (RSP = 0.48) and has a diameter of 2 mm where the conch diameter is 22 mm. The septal necks are very short adnate, the connecting ring is not preserved.

Remarks

The species was described in detail by Teichert (1930). The new data suggest an ontogenetic change of the position of the siphuncle from central in early growth stages to eccentric in later growth stages.