Cyrtogomphoceras troedssoni Teichert, 1930

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 : 101-102

Cyrtogomphoceras troedssoni Teichert, 1930

Figs 37B, 38C–D

Cyrtogomphoceras (?) troedssoni Teichert, 1930: 296–297 , pl. 8 figs 32–33.

Faberoceras troedssoni – Flower 1946: 452.

Cyrtogomphoceras (?) troedssoni – Balashov 1953a: 208.

Faberoceras? troedssoni – Flower in Flower & Teichert 1957: 66, 91, text-fig. 27.

Diagnosis

Small Cyrtogomphoceras with conch height of mature body chamber ca 40 mm, slightly compressed conch cross section (CHI ca 1.1) and irregularly, transversally constricted and undulating conch surface; sutures straight, directly transverse; siphuncle marginally located with very widely expanded segments; septal necks cyrtochoanitic, recumbent; small to moderate endosiphuncular bulletes.

Material examined

ESTONIA • 1 spec.; Hiiumaa Island, Kõrgessaare quarry; Kõrgessaare Formation , Vormsi Regional Stage ; GIT 426-392 - 1 • 1 spec.; same data as for preceding; TUG 939-60 .

Description

GIT 426-392-1 ( Fig. 38D) is a fragment of an endogastrically curved phragmocone and mature body chamber, with the outer shell partly preserved. The conch surface is hidden under an overgrowth of epibionts, but a fine transverse striation is visible on the inner mold of parts of the body chamber. At the base of the mature body chamber, the conch height and width are 40 mm and 35 mm, respectively (CHI = 1.14). The conch cross section has an oval shape with a narrower prosiphuncular side. The body chamber is at least 43 mm long and slightly curved with a convex antisiphuncular margin and a concave prosiphuncular margin. At its adoral end, the height of the body chamber is 38 mm. The peristome is either not preserved, or only very fragmentarily preserved. In lateral view, the entire specimen (body chamber and phragmocone) appears slightly irregularly undulated with shallow constrictions at irregular distances. The phragmocone has a height of 30–40 mm at a length of 36 mm (angle of expansion = 15°). The sutures are straight and directly transverse and 7 mm apart where the conch height is 35 mm (RCL = 0.2). The siphuncle is marginal and very wide, it is too poorly preserved to measure the septal foramen. The segments have a height of 9 mm where the chamber length is 6 mm, and the conch height is 32 mm (SCR = 1.5).

The second specimen TUG 939-60 is a short fragment of the phragmocone and body chamber, showing the typical irregular undulation of the shell ( Fig. 38C). At a conch height of 40 mm, the conch width its 35 mm, similar to GIT 426-392-1. The sutures are straight and directly transverse. The siphuncle and septal necks are well-preserved in this specimen (Fig. 37B). The siphuncle is very wide; the septal foramen has a height of 9 mm and the siphuncular segments expand toward 15 mm where the chamber length is 5 mm, the conch height is 40 mm (RSH = 0.23, RSS = 1.67, SCR = 3). The connecting ring is thin, the septal necks are cyrtochoanitic recumbent and small endosiphuncular bullettes are present.

Remarks

This species is unique to Cyrtogomphoceras with regard to its relatively small size (the type species C. magnum Whiteaves, 1890 has a conch length of ca 270 mm) and its slightly irregularly undulated shell. C. cf. thompsoni Miller & Furnish, 1937 , from the late Katian of Norway ( Sweet 1959) is more curved, slightly larger (ca 70 mm maximum conch height) and the adoral-most sutures are more oblique than in C. troedssoni Teichert, 1930 .