Hemicoanella occulta, 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 : 48-49

Hemicoanella occulta sp. nov.

urn:lsid:zoobank.org:act:F8F91097-8EF4-454F-8317-F4AA1A270616

Figs 32C , 33A–B

Diagnosis

Hemichoanella with ca three directly transverse annulations at distance similar to conch diameter and ornamented additionally with finely transverse striae; conch cross section circular; angle of expansion ca 5°; relatively wide marginal siphuncle with rSD of 0.36; septal necks hemichoanitic.

Etymology

From ‘hidden’, in Latin ‘ occultus ’, because of its Catoraphiceras -like external morphology.

Type material

Holotype Specimen FMNH-P30420 ; by monotypy.

Type locality and horizon

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

Description

The holotype is a ca 17 mm long fragment of a phragmocone with a slightly compressed or circular conch cross section with a conch height of 7–8.4 mm (angle of expansion ca 5°). The conch is annulated with ca three directly transverse annulations at a distance similar to the corresponding conch cross section. Additionally, it is ornamented with ca 10 fine striae that run parallel to the annuli. The sutures are directly transverse at the flanks and at the antisiphuncular side and are not exposed at the prosiphuncular side. The chambers have a distance of ca 2.1–2.5 mm (3–4 chambers per corresponding conch cross section). The septal position does not correspond with the position of the annuli, some septa occur in the valleys, others in the rings of the annuli. The siphuncle is marginal and relatively large with a diameter of ca 3 mm at the adoral end of the specimen (rSD = 0.36). The connecting ring is not preserved. The septal necks are hemichoanitic, 0.6–1 mm long.

Remarks

The internal characters of this species are similar to those of H. canningi Teichert & Glenister, 1954 , hitherto the only known species of Hemichoanella ‚ which, however, has a smooth shell. Externally H. occulta sp. nov. is similar to species of Catoraphiceras , which differ in having shorter, orthochoanitic septal necks. Notocycloceras yurabiense Teichert & Glenister, 1954 differs in having subholochoanitic septal necks. Anthoceras warburtoni Teichert & Glenister, 1954 , A. arrowsmithense Stait & Laurie, 1985 , and Notocycloceras yurabiense Teichert & Glenister, 1954 differ in having subholochoanitic septal necks. The siphuncle of Anthoceras xerxes (Billings, 1865) is wider (rSD = 0.43). The Siberian forms A. angarense Balashov, 1960 and A. bajkitense Balashov, 1960 differ in having less well pronounced annulations and a narrower septal spacing, with ca 10 chambers per distance similar to the corresponding conch diameter, and A. sibiricum Balashov, 1962 has an extremely wide siphuncle with an rSD of ca 0.5.

Figures

Fig. 32. Reconstruction and interpretation of details of connecting ring and septal necks in orthoconic cephalopods from the Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A. Catoraphiceras sp., FMNH-P30425, dorsal side of the connecting ring, see Fig. 10A. B. Cyptendoceratid gen. et sp. indet., FMNH-P30431, see Fig. 31B. C. Hemichoanella occulta sp. nov., FMNH-P30420, from bed PO 131, dorsal side of the connecting ring, see Fig. 36B. Black: septal neck and septum. Dark grey: connecting ring. Without scale.

Fig. 33. Median sections of phragmocones. A–B. Hemichoanella occulta sp. nov., from bed PO 131. C–E. Eosomichelinoceras borealis sp. nov., from bed PO 123.3, Olenidsletta Member, Floian, Ordovician, Profilstranda section, Ny Friesland, Spitsbergen. A–B. Specimen FMNH-P30420, holotype. C. Specimen FMNH-P30305. D. Specimen FMNH-30288. E. Specimen FMNH-30284. Scale bars: A–B, E = 5 mm; C–D = 1 mm.