Strandoceras kohilense, Kröger, 2025

Strandoceras kohilense sp. nov.

urn:lsid:zoobank.org:act:8C055DE8-1F47-4517-8965-EA9C4D8E8EF5

Figs 43C View Fig , 44B View Fig

Diagnosis

Strandoceras with drop-shaped conch cross section, narrower at the dorsal conch margin; mature body chamber nearly tubular in shape, slightly curved with maximum conch height of ca 50 mm; distinct hyponomic sinus on concave conch margin.

Type material

Holotype

ESTONIA • Kohila quarry ; Kõrgessaare Formation , Vormsi Regional Stage; TUG 47-883 .

Paratypes

ESTONIA • 2 specs; Vormsi Island, Saxby shore ; Kõrgessaare Formation , Vormsi Regional Stage; GIT 426-1136 View Materials , GIT 878-79 View Materials .

Description

The most complete specimen is TUG 47-883 ( Fig. 44C View Fig ), which is an endogastrically curved fragment of a mature body chamber and four chambers of the phragmocone. The conch surface is not preserved. At the base of the body chamber the height and width are ca 47 mm and 27 mm, respectively (CHI = 1.74), and the elliptically compressed conch cross section has narrow dorsal and ventral margins. The specimen is probably slightly deformed (compressed). The body chamber is in its length of 47 mm completely preserved (RBL = 1). At the aperture, a distinct hyponomic sinus is present on the prosiphuncular side. In lateral view, the prosiphuncular margin is concave and the antisiphuncular margin convex, resulting in a curved tubular shape of the mature body chamber. The angle of expansion of the phragmocone near the base of the body chamber is low (3°), increasing in height between 46 mm and 47 mm at a length of 18 mm. The sutures form shallow lateral lobes and distinct, narrow saddles near the location of the siphuncle; they are 7 mm apart where the conch height is 47 mm (RCL = 0.15). The siphuncle and the septal foramen are too poorly preserved to be measured. The position of the siphuncle is nearly marginal.

Specimen GIT 426-1136 is a fragment of four chambers of the phragmocone and a mature body chamber of nearly identical to TUG 47-883. It is less deformed, and details of the septal foramen are better preserved. At the base of the body chamber, the height and width are 48 mm and 35 mm, respectively (CHI = 1.37). The body chamber is 47 mm long, curved and nearly tubular in lateral view. The sutures form wide lateral lobes and narrow, distinct saddles at the location of the siphuncle, they are 7 mm apart where the conch height is 50 mm (RCL = 0.14). The septal foramen is near the conch margin.

The details of the siphuncle and septal neck are preserved in specimen GIT 878-79 ( Fig. 44B View Fig ). At a conch height of 47 mm, a chamber is 6 mm long, the septal foramen in 4.5 mm high, and the siphuncular segments expand toward a height of 9 mm (RSH = 0.1, RSS = 2, SCR = 1.5). The connecting ring is thin, and the septal necks are cyrtochoanitic. Simple, small endosiphuncular bullettes are present. The connecting ring is hyposeptally adnate.

Remarks

The adult size of S. kohilense sp. nov. (mature conch height ca 50 mm) is smaller than in S. kalevipoegi sp. nov., S. sphynx , S. sulevipoegi sp. nov., S. tyriense , and S. muhvi sp. nov. The species S. schmidti differs from S. kohilense in having a wider angle of expansion. Strandoceras kohilense differs from the other species in having at the base of the mature body chamber, a drop-shaped conch cross section with a margin which is narrower at the dorsal side than on the ventral side. This difference could suffice to erect a new genus. However, nothing is known about the ontogenetic change of the conch cross section in this species, and it cannot be ruled out that the conch cross section is slightly deformed by taphonomic processes. More material is needed to evaluate the differences between this species and the type species of Strandoceras .