Cyclostomiceras profilstrandense, Kröger & Pohle, 2021

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 : 15-16

Cyclostomiceras profilstrandense sp. nov.

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Fig. 5O–Q

Diagnosis

Small Cyclostomiceras with adult conch width of ca 14 mm, slightly depressed conch cross section; ornamented with shallow, widely spaced, directly transverse annulations.

Etymology

Referring to the type locality.

Type material

Holotype Specimen FMNH-P30336 , by monotypy.

Type locality and horizon

Profilstranda section, adjacent to Hinlopenstretet, Spitsbergen, from bed Po123.3, 120.3 m above base of Olenidsletta Member, V 2a trilobite zone, Blackhillsian, Floian.

Description

Specimen FMNH-P30336 is a fragment of part of the phragmocone and a nearly complete body chamber. At the base of the body chamber the cross section is slightly depressed, the conch height is 11.8 mm, the width 12.3 mm (rW = 1.08). The maximum conch width is 13.7 mm and reached at ca mid-length of the body chamber. The length of the body chamber is 11 mm, and its aperture is simple transverse and slightly contracted with a width of 13.5 mm (angle of expansion of conch width 6°).

The conch surface is ornamented with widely rounded annuli which have a distance of ca 3 mm in distance (ca 0.25 of corresponding conch height). Additionally, distinct, irregularly spaced growth lines occur. The annuli and the growth lines form a shallow hyponomic sinus at the prosiphuncular side of the conch.

The chamber spacing is narrow with a distance between two septa of ca 1.3 mm at an assumed conch height of ca 11 mm. The sutures form a very shallow lateral lobe. The siphuncle is preserved in the last chamber, and has a thickness of ca 1.1 mm and a distance from the conch margin of 0.8 mm and is presumably tubular.

Comparison

The conch shape and conch dimensions are almost identical to those of Cyclostomiceras minimum (Whitfield, 1886) from the Fort Cassin Formation, Vermont, USA (see Ulrich et al. 1943). However, the new species differs in possessing a weakly ornamented conch surface.

Figures

Fig. 5. Cyrtoconic cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A–C. Lawrenceoceras larus sp. nov., FMNH-P30351, holotype, from bed PO 131. A. Lateral view with siphuncle on left side. B. Ventral view, prosiphuncular side. C. Adoral view of septum and septal perforation.D–E. Lawrenceoceras ebenus sp. nov., FMNH-P30335, holotype, from bed PO 123.3. D. Lateral view with siphuncle on left side. E. Ventral view, prosiphuncular side. F–G. Olenidslettoceras farmi gen. et sp. nov., FMNH-P30334, holotype, from bed PO 123.3. F. Lateral view with siphuncle on left side. G. Ventral view, prosiphuncular side. H–N. Vallhalloceras floweri King & Evans, 1990. H–I. Specimen FMNH-P30337, from bed PO 131. H. Lateral view, siphuncle on right side I. Ventral view, prosiphuncular side. J–L. Specimen FMNH-P30343 from bed PO 123.3, J. Lateral view with siphuncle on left side. K. Ventral view, prosiphuncular side. L. Dorsal view, antisiphuncular side.M–N. Specimen FMNH-P30338 from bed PO 131. M. Lateral view with siphuncle on left side. N. Ventral view, prosiphuncular side. O–Q. Cyclostomiceras profilstrandense sp. nov., specimen FMNH-P30336, from bed PO 123.3. O. Lateral view with siphuncle on left side. P. Ventral view, prosiphuncular side. Q. Dorsal view, antisiphuncular side. Scale bar = 10 mm for all figures.