Schuchertoceras deformis Kröger 2025
Creators: name: Kröger, Björn
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Ascoceratidae
Schuchertoceras
Schuchertoceras deformis

description: Schuchertoceras deformis (Eichwald, 1860) comb. nov.
Fig. 36D, F–G
Ascoceras deforme Eichwald, 1860: 1192, pl. 42 fig. 18.
Billingsites deformis – Foerste 1929: 157, pl. 20 fig. 3. ― Strand 1934: 54–55, pl. 4 fig. 7. ― Frye 1982: 1278.
non Billingsites deformis – Sweet & Miller 1957: 43, pl. 4 figs 1–2.
Diagnosis
Schuchertoceras with three ascoceroid septa which are detached from each other throughout their entire length; with elliptically depressed conch cross section and nearly straight growth axis in ascoceroid growth stages.
Material examined
ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 46-138 • 1 spec.; Läänemaa, Uuemõisa; Adila Formation, Pirgu Regional Stage; TUG 2-734 • 1 spec.; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-191.
Type locality and horizon
Kõrgessaare quarry, Hiiumaa Island; Kõrgessaare Formation, Vormsi Regional Stage.
Description
TUG 2-734 is the most complete specimen (Fig. 37F–G), which preserves an almost complete ascoceroid portion of the conch including the basal septum, three ascoceroid septa and the nearly complete mature peristome. The width of the specimen is 36 mm at the basal septum, 47 mm at approximate, mid-length where it reaches its maximum width, and 35 mm at the aperture. The conch cross section is elliptically depressed (CHI: 0.75–0.85), but not completely preserved in portions between ca 20 mm from the aperture and 10 mm from the apical end. At the aperture, the height is 28 mm; at the basal septum the height can be reconstructed as ca 27 mm and its maximum height can be reconstructed as ca 40 mm. In lateral view, the conch is nearly straight and egg-shaped with a rounded but narrow apical tip and a constricted adoral part with a simple straight peristome. The ventral (prosiphuncular) margin of the peristome is poorly preserved, and the presence of a shallow shallow hyponomic sinus cannot be excluded. The maximum height is reached at ca 25 mm from the aperture. The basal suture is directly transverse at ca 17 mm from the apical end of the specimen. On the dorsum, the respective distances of the ascoceroid sutures from the peristome are 8 mm, 14 mm, and 23 mm. In lateral view, they form a pointed lateral lobe at ca 10 mm from the basal septum and a wide lateral sinus.
The ventral part and the interior of the basal septum are well-preserved in TUG 46-138. The ventral part is shallowly convex in lateral view and in cross section. The basal septum is located at a conch width of 38 mm and the septal foramen is in a nearly marginal position (ca 2 mm from ventral margin) with a diameter of ca 4 mm (RSH = 0.1, RSP = 0.06).
The third specimen (GIT 878-191) is a poorly preserved, deformed fragment of an ascoceroid conch with the three ascoceroid sutures and a straight peristome preserved (Fig. 36D).
Remarks
These specimens can be referred to Ascoceras deforme Eichwald, 1860 based on the three ascoceroid septa, which are clearly visible in Eichwaldʼs (1860: pl. 49 fig. 18) figures. There, the basal septum is not figured or is not preserved, which is the reason why this species was classified within Billingsites Hyatt, 1884 in Foerste (1929) and Strand (1934). Strand’s (1934) identification of the genus was questioned by Frye (1982: 1278) but the poorly preserved material to hand at the time did not permit a solution to the problem. The faint suture of the basal septum can easily be overlooked. In the material described above it is best visible in specimen TUG 46-138.
Comparison
Schuchertoceras deformis differs from the two species of Schuchertoceras known from the Boda Limestone of Dalarna, Sweden in having three instead of two (in S. bodense Frye, 1982) or one (in S. troedssoni (Foerste, 1929)) ascoceroid septa, and in its more slender conch. It differs from North American species of Schuchertoceras in having ascoceroid sutures which are detached from each other throughout their entire length (compare Frye 1982: fig. 3a–j).
The specimen described under Billingsites deformis (Eichwald, 1860)? by Sweet & Miller (1957) does not belong to this species because it has less than three ascoceroid septa and probably no basal septum. Additionally, the shape of the ascoceroid septum, visible in Sweet & Miller (1957: pl. 4 figs 1–2) differs considerably from that of the Estonian specimens in that it is less strongly curved.
description: Published as part of Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, pp. 1-169 in European Journal of Taxonomy 978 on pages 96-97, DOI: 10.5852/ejt.2025.978.2801, http://zenodo.org/record/14988376