Discosorida, Flower, 1950

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 : 126

Discosorida fam., gen. et sp. indet. C

Fig. 46C–D

Material examined

ESTONIA • 1 spec.; Hiiumaa Island; Kõrgessaare quarry , Vormsi Regional Stage; TUG 1745-284 .

Description

The specimen is a mold of a complete mature body chamber. The outer shell is not preserved. The base of the body chamber has a height and width of 40 mm and 28 mm, respectively (CHI = 1.43). The body chamber is 28 mm long (RBL = 0.7). In lateral view, the antisiphuncular margin is convex and the prosiphuncular margin straight or only slightly convex near the aperture. The peristome is simple and straight, a faint hyponomic sinus is present on the prosiphuncular side. The adoralmost ca 5 mm of the body chamber are contracted. At the base, a ca 5 mm a wide band of oncomyarian, buttressed muscle scars is present. The suture is straight and directly transverse. The septal foramen is 5 mm wide and imprints on the septal mode suggest an expanded siphuncular segment with a width of at least 10 mm (RSH = 0.13, RSS = 2).

Remarks

This specimen (probably a cyrtogomphoceratid) is very similar in shape to GIT 426-1100 ( Discosorida fam., gen. et sp. indet. B) but it is smaller (height at base of body chamber: 40 mm, against 60 mm in the latter). More, and better persevered material is needed to evaluate the features of the siphuncle to assign this specimen to a (new) species.

Figures

Fig. 46. Fragments of indeterminate Discosorida Flower, 1950 of the Vormsi Regional Stage, Estonia. A–B. Discosorida fam., gen. et sp. indet. B, specimen GIT 426-1100 from Paluküla quarry. A. Lateral view. B. Adapical view. C–D. Discosorida fam., gen. et sp. indet. C, specimen TUG 1745-284 from Kõrgessaare quarry, Hiiumaa Island. C. Lateral view. D. Adapical view. E–F. Discosorida fam., gen. et sp. indet. D, specimen TUG 1827-162 from Sutlema old quarry. E. View of the prosiphuncular side. F. Adapical view, note the discosoroid-like siphuncle. G. Adoral view, note the Kiaeroceras-like crosssection. Scale bar = 20 mm, same scale in all figures.