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 : 124-125

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

Fig. 45A–B

Material examined

ESTONIA • 3 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation , Pirgu Regional Stage; GIT 878-188 to GIT 878-190 • 1 spec.; Salu ; Pirgu Regional Stage; TUG 1745-26 .

Description

All four specimens are isolated, endogastrically curved mature body chambers, without phragmocone parts. They are identical in size and shape. At the base, their height is 44–45 mm, at the aperture the height measures 36–37 mm, and the total length from base to aperture is ca 50 mm. The three specimens from Vohilaid Island are likely to be slightly deformed (compressed) with a width of ca 29 mm at the body chamber base (CHI = 1.5). In specimen TUG 1745-26, the width is 30 mm where the height is 42 mm (CHI = 1.4). The conch cross section is rounded elliptical at mid body chamber position. At the base of the body chamber, the antisiphuncular margin is more narrow, almost rounded angular. In this latter specimen, traces of a fine transverse annulation are preserved, which is directly transverse, indicating that no hyponomic sinus occurs at the peristome. In lateral view, the antisiphuncular margin is convex and the prosiphuncular margin concave. The conch height decreases nearly continuously toward the aperture resulting in maximum conch heights at or near the base of the body chamber. The siphuncle is nearly marginal, but in all specimens is too poorly preserved to be measured in all specimens.

Remarks

The endogastrically curved and contracted body chambers indicate that these belong to an unknown discosorid species, probably a cyrtogomphoceratid. The form of the body chamber (curved, contracted) in combination with a marginal siphuncle is unknown from any multiceratoid genus. However, because details of the siphuncle and the phragmocone remain unknown a firm determination and erection of a new taxon is not possible with the available material.

Figures

Fig. 45. Fragments of indeterminate Multiceratoidea Mutvei, 2013 of the Vormsi–Pirgu regional stages, Estonia. A–B. Discosorida fam., gen., et sp. indet. A, Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage. A. Specimen GIT 878-188, lateral view. B. Specimen GIT 878-189, adapical view, position of the siphuncle toward the right. C–E. Multiceratoidea fam., gen., et sp. indet. A. C. Specimen GIT 840- 269, from Hosholm shore (tower) Pirgu Regional Stage, lateral view. D–E. Specimen GIT 878-76, from Saxby shore, Vormsi Island, Vormsi Regional Stage. D. Lateral view. E. View of the concave side of conch curvature, position of siphuncle unknown. Scale bar = 20 mm, same scale in all figures.