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 : 125-126

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

Fig. 46A–B

Material examined

ESTONIA • 1 spec.; Hiiumaa Island, Paluküla quarry ; Kõrgessaare Formation , Vormsi Regional Stage; GIT 426-1100 .

Description

The specimen is a fragment of a slightly endogastrically curved body chamber and two chambers of the phragmocone. The outer shell is not preserved. At the base of the body chamber, the conch height is 60 mm. The reconstructed width is 48 mm (CHI = 1.25). The conch cross section is elliptically shaped with narrow dorsal and ventral margins. In lateral view, the prosiphuncular side is concave and the antisiphuncular side convex, resulting in a slightly curved shape and a decreasing conch height. At the adoral-most parts, ca 20–30 mm from the aperture, the margins are slightly more curved, resulting in a slightly ventrally shifted apertural opening. At the aperture, the height is 52 mm. At its base a ca 7 mm wide band with oncomyarian, buttressed muscle scars is present. A hyponomic sinus is preserved on the prosiphuncular side, it is ca 10 mm deep. The body chamber is 53 mm long (RBL = 0.88).

The sutures are straight and slightly deflected adorally at the antisiphuncular side, with shallow saddles at the antisiphuncular side. The two adoral-most sutures are crowded (ca 5 mm apart), the second chamber has a length of ca 8 mm at a conch height of 60 mm (RCL = 0.13). On the adoral-most septum the septal foramen is 9 mm wide and traces of the siphuncular segments indicate a maximum expansion of the siphuncular segments to at least 15 mm (RSH = 0.15, RSS = 1.7, SCR = 1.9).

Remarks

The endogastric condition and the widely expanded siphuncle with weak or absent bullettes indicate that this specimen probably represents an unknown cyrtogomphoceratid species. The specimen differs from species of Strandoceras in having a short, contracted mature body chamber. The size of the specimen and the position and size of the siphuncle suggest that this specimen could be related to Westonoceras estonicum Balashov, 1959 , another likely cyrtogomphoceratid species (not related to Westonoceras ), which is known only from a single fragmentarily preserved phragmocone from late Katian strata of Tapa, Estonia. More material is needed to test this hypothesis.

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.