Strandoceras kalevipoegi, Kröger, 2025

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 : 117-119

Strandoceras kalevipoegi sp. nov.

urn:lsid:zoobank.org:act:23EA0987-FD52-4193-98AA-54A085118FB8

Fig. 41E , 42A

Diagnosis

Large Strandoceras reaching conch heights of 80 mm; phragmocone strongly endogastrically curved with angle of expansion of up to 35°; mature body chamber ca 80 mm long, contracted, and nearly straight with greatest height at the adapical half of its length; conch surface smooth or with very fine growth lines.

Etymology

From Kalevipoeg, the main hero in the Estonian national epic, Friedrich R. Kreutzwaldʼs (1803–1882) poem ”Kalevipoeg”, referring to the large size of this species.

Type material

Holotype

ESTONIA • Kohila quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-431 .

Paratypes

ESTONIA • 2 specs; Vormsi Island , Saxby shore (S); Kõrgessaare Formation, Vormsi Regional Stage; TUG 899-54 , TUG 899-89 • 1 spec.; Sutlepa quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 80-509 .

Description

The holotype is a fragment of parts of an endogastrically curved phragmocone and a mature body chamber, partly preserving the outer shell. The conch surface is preserved near the base of the peristome, where it is smooth or with very fine growth lines, only. In lateral view, the conch margin at the antisiphuncular side is convex throughout the entire length. The prosiphuncular side of the conch margin is concave on the phragmocone and nearly straight on the body chamber. At the base of the body chamber, the conch height is 75 mm. The greatest conch height of 80 mm is located in the lower part of the body chamber, ca 30 mm from its base. The body chamber is ca 80 mm long. The conch cross section of the specimen is not preserved but it was apparently compressed with an oval shape, slightly narrower on the prosiphuncular side with a reconstructed CHI of ca 1.6 at the base of the body chamber. The phragmocone expands with an angle of expansion of up to 14°at conch heights between 62 mm and 72 mm. The sutures form very shallow lateral lobes and distinct narrow saddles on the prosiphuncular side of the conch; they are ca 9 mm apart where the conch height is 72 mm (RCL = 0.13). The peristome is straight and simple with a deep (ca 15 mm) hyponomic sinus on the prosiphuncular side.

The more strongly curved apical sections of the phragmocone are preserved in specimen TUG 899-89. The conch cross section is oval compressed with a narrower margin on the prosiphuncular side. The conch height and width are 36 mm and 32 mm, respectively (CHI = 1.13). The conch expands with an angle of expansion of 35° between conch heights 33 mm and 49 mm.

The details of the siphuncle and the septal necks are well-preserved in specimen TUG 80-509. There, the siphuncle is marginal, the septal foramen has a width of 9 mm, the siphuncular segments expand to 15 mm in height, and the chamber length is 5 mm, where the conch height is 66 mm (RSH = 0.14, RSS = 0.6, SCR = 3). The septal necks are cyrtochoanitic and thick endosiphuncular bullettes are present.

Comparison

This species is unique among Strandoceras in reaching adult conch heights of 80 mm, in having a nearly smooth conch surface, and in having a long, nearly straight mature body chamber, which contrasts with the curved rapidly expanding phragmocone.

Figures

Fig. 41. Large species of Strandoceras Flower, 1946 of the Vormsi–Pirgu regional stages, Estonia. A. Strandoceras sphynx (Schmidt, 1858), specimen TUG 1672-29 from Saxby village, Vormsi Island, Pirgu Regional Stage. B. Strandoceras sulevipoegi sp. nov., holotype TUG 1745-209, from Salu, Pirgu Regional Stage. C. Strandoceras muhvi sp. nov., holotype TUG 42-432, from Kohila quarry, Vormsi Regional Stage. D. Strandoceras sulevipoegi, paratype TUG 42-399, from Vormsi Island, Vormsi–Pirgu regional stages. E. Strandoceras kalevipoegi sp. nov., holotype TUG 42-431, from Kohila quarry, Vormsi Regional Stage. F. Strandoceras sphynx (Schmidt, 1858), specimen TAM G432:68 from Niibi hillock, Läänemaa, Pirgu Regional Stage. Scale bar = 20 mm, same scale in all figures, all in lateral view.

Fig. 42.Diagrams of variabilityinconch growth in speciesof Strandoceras Flower, 1946.A. S. kalevipoegi sp. nov. = diamonds; S. sphynx (Schmidt, 1858) = white circles; S. sulevipoegi sp. nov. = black circles. B. S. muhvi sp. nov. = crosses; S. schmidti = stars. Note that distinction of species in conch fragments with conch heights <50 mm is not possible based on angle of expansion. Negative angles indicate decreasing conch heights.