Nyfrieslandoceras bassleroceroides, 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 : 72-73

Nyfrieslandoceras bassleroceroides gen. et sp. nov.

urn:lsid:zoobank.org:act:9E26DE1D-597E-4248-BC5C-6CB9461B66D2

Figs 8D , 45A–B , 49B–C

Diagnosis

As for genus, by monotypy.

Etymology

Referring to Bassleroceras Ulrich & Foerste, 1936 because of its superficial similarity with this genus.

Type material

Holotype Specimen FMNH-P30353 .

Paratype Specimen FMNH-P30356 from type horizon and locality .

Type locality and horizon

From Profilstranda section, Ny Friesland, Spitsbergen, bed PO 131, 128 m above base of Olenidsletta Member, V 2b trilobite zone, Blackhillsian, Floian.

Description

The type specimen is a 62 mm long fragment of a phragmocone and a complete body chamber ( Fig. 45A– B ). The conch is slightly curved with a marginal siphuncle on the convex side of the conch curvature. The preserved portion of the phragmocone has a height of 13–18 mm and a width of 11–13 mm (9°angle of expansion of conch height). The body chamber is simple tubular, 30 mm long and has a height of 18–20 mm and a width of 13–14 mm (4° angle of expansion of conch height). The body chamber is moderately compressed (with ratio conch width /conch height ca 0.7), but the more adapical parts of the fragment are less compressed (rW ≈ 0.85).

The conch surface is ornamented with prominent irregularly spaced growth lines which form a distinct hyponomic sinus on the convex, prosiphuncular side of the conch curvature.

The siphuncle is thin (rSD = ¹/16), nearly marginal, and slightly expanded within the chambers. The septal necks are thickened and very short orthochoanitic or achoanitic ( Figs 8D , 49B–C ). The sutures are obliquely transverse, form wide lateral lobes and bent forward on the convex side of the shell. Approximately nine chambers occur per length similar to the corresponding conch height at the base of the body chamber. The chamber length is 2 mm at a conch height of 18 mm. Cameral and/or endosiphuncular deposits not known.

Comparison

This species is externally similar to a slender Bassleroceras Ulrich & Foerste, 1936 , but differs in having an expanded siphuncle with peculiar, very short or achoanitic, thickened septal necks, known otherwise only from Richardsonceras Foerste, 1933 and Richardsonoceroides Chen, 1987 . The former genus is strongly curved and has a contracted adult body chamber. The latter genus is less compressed, smaller and more curved. Nyfrieslandoceras bassleroceroides gen. et sp. nov. can be conveniently classified within the Phthanoncoceratidae because of its combination of characteristic septal necks, nearly tubular siphuncle and exogastric conch curvature.

Figures

Fig. 8. Reconstruction and interpretation of details of connecting ring and septal necks in cyrtoconic cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A. Lawrenceoceras ebenus sp. nov., FMNH-P30335, holotype, see also Fig. 7B. B. Vallhalloceras floweri Evans & King, 1990, FMNH-P30340, see also Fig. 50B. C. Olenidslettoceras farmi gen. et sp. nov.,FMNH-P30334, holotype, see also Fig. 50A.D. Nyfrieslandoceras bassleroceroides gen. et sp. nov., FMNH-P30353, holotype, see also Fig. 49C. Black: septal neck and septum. Dark grey: connecting ring. Light grey: cameral deposits. Without scale.

Fig. 45. Cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A–B. Nyfrieslandoceras bassleroceroides gen. et sp. nov., FMNH-P30353, holotype, from bed PO 131. A. Ventral view, prosiphuncular side. B. Lateral view with ventral, prosiphuncular side toward the left. C–D. Order, gen. et sp. indet. A, FMNH-P30354, from bed PO 131. C. Dorsal (?) view. D. Lateral view, with dorsal (?), antisiphuncular side toward the right. E–F. Estonioceratid gen. et sp. indet.A., FMNH-P30342, from bed PO 7.5. E. Lateral view with ventral, prosiphuncular side toward the right. F. adoral view with preserved siphuncular perforation. G. Order, gen. et sp. indet. B, FMNH-P30424, from bed 4.8., lateral view with ventral, prosiphuncular side toward the right. Scale bar = 10 mm for all figures.

Fig. 49. Median sections of phragmocones of cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A. Order, gen. et sp. indet. B, FMNH-P30424, from bed 4.8, see also Fig. 11A for interpretation. B–C. Nyfrieslandoceras bassleroceroides gen. et sp. nov., FMNH-P30353, holotype, from bed PO 131. B. Detail with septa and siphuncle preserved, septa are crushed and taphonomically distorted. C. Detail of septal necks and connecting ring, see Fig. 8D for interpretation. Scale bars: A–B = 5 mm; C = 1 mm.