Cyptendoceras sp. B

Kröger, Björn & Pohle, Alexander, 2021, Early-Middle Ordovician cephalopods from Ny Friesland, Spitsbergen - a pelagic fauna with Laurentian affinities, European Journal of Taxonomy 783 (1), pp. 1-102 : 45

Cyptendoceras sp. B

Figs 12A , 31C

Material examined

Specimens FMNH-P30166 and FMNH-P30472 , from Profilbekken river basin , locality PR-phosphatic , adjacent to Hinlopenstretet, Spitsbergen , uppermost Olenidsletta Member , V3 trilobite zone , Dapingian .

Description

The larger specimen, FMNH-P30166, is a fragment of a phragmocone with smooth shell, a circular or slightly compressed conch cross section with diameters 31–38 mm and a length of 82 mm (angle of expansion ca 5°). The siphuncle is marginally positioned, is subcircular or slightly depressed in cross section with a height of 11.5 mm, where the conch height is 36 mm (rSD = 0.32). The septa are imploded and crushed. Where visible they are 5 mm apart at a conch height of 34 mm (rCL = 0.15) with the sutures forming a distinct ventral lobe. The septal necks are loxochoanitic with a length of 1.2–1.7 mm where the siphuncular segment is 5 mm long (0.24–0.34 of chamber length). The connecting ring is slightly concave and poorly preserved, making an estimation of its thickness impossible ( Fig. 31C ).

The second specimen, FMNH-P30472 ( Fig. 12A ), is a 20 mm long apical portion of a phragmocone with a smooth outer surface and a slightly compressed conch cross section. This fragment is slightly curved with the siphuncle marginally positioned at the concave side of conch curvature. The siphuncle is empty and apparently circular in cross section, with a diameter of 1.4 mm where the conch height is 4 mm. The extreme apex is cup-shaped without constriction and grows from its extreme tip toward a conch height of 1.3 mm within the apical 1 mm; at a distance of 2 mm from the tip the conch is 1.7 mm high, at a distance of 5 mm the conch height is 2.3 mm. The angle of expansion between 1 mm from tip toward the adoral end of the specimen is ca 7°.

Remarks

These specimens are assigned to Cyptendoceras because they combine a relatively wide marginal siphuncle and (in the larger specimen) concave segments, loxochoanitic septal necks and a ventral sutural lobe, although the preserved parts of the siphuncle are empty. Most species of Cyptendoceras have a narrower chamber spacing and a slightly depressed cross section. In C. mesleri Ulrich, Foerste, Miller & Unklesbay, 1944 only five chambers occur in a distance similar to conch height, which is comparable to the rCL of specimen FMNH-P30166. However, neither C. mesleri nor the specimens described above allow for detailed comparison and the fragmentary character of the available specimens do not allow for a species level determination.

Figures

Fig. 12 (previous page). Apical parts of orthoconic cephalopods from the Olenidsletta Member, Floian, Ordovician, near Hinlopenstretet, Ny Friesland, Spitsbergen. A. Cyptendoceras sp. B., FMNH-P30472 from Profilbekken river basin, locality PR-phosphatic. Lateral view with siphuncle toward the left. B. Svalbardoceras sterna gen. et sp. nov, FMNH-P30169, from PO 7.5. Lateral view with siphuncle toward left. C, F–G. Eosomichelinoceras borealis sp. nov. C. Specimen FMNH-P30171, from bed PO 123.3. Lateral view with prosiphuncular side toward the right. D. Bactroceras fluvii sp. nov., FMNH-P30168, from Profilbekken river basin, locality PR-phosphatic, showing the ventral side with ventral sutural lobe. E, H, J. Bactroceras boliviensis Aubrechtová, 2015 from bed PO 131. E. Specimen FMNH-P30165, nearly dorsal view, showing the transition of the extreme apical part toward the juvenile part of the conch. F. Specimen FMNH-P30182, lateral view with siphuncle toward the right. G. Specimen FMNH-P30184, lateral view with siphuncle toward the left. H. Specimen FMNH-P30183, apical view, showing the smooth apical surface of the protoconch. I. Ethanoceras solitudines gen. et sp. nov., FMNH-P30173, from bed PO 123.3, note the fine transverse striation. J. FMNH-P30160, showing details of fine transverse ornamentation. Scale bar = 2 mm for all figures.

Fig. 31. Median section of details of septal necks and siphuncle of cyptendoceratids from Olenidsletta Member, adjacent to Hinlopenstretet, Spitsbergen. A–B. Cyptendoceratid gen. et sp. indet., FMNH-P30431 from bed PO 131, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. Dorsal side directed toward left. A. General view of the siphuncle. Scale bar = 2 mm. B. Details of dorsal side of connecting ring. Scale bar = 1 mm. C. Cyptendoceras sp. B, FMNH-P30166 from Profilbekken river basin, locality PR-phosphatic, uppermost Olenidsletta Member, V3 trilobite zone, Dapingian. Scale bar = 5 mm.