Early-Middle Ordovician cephalopods from Ny Friesland, Spitsbergen - a pelagic fauna with Laurentian affinities Author Kröger, Björn 72F166B6-51DC-4DD8-9DEE-47EDDEE3D2F2 Finnish Museum of Natural History, University of Helsinki, PO Box 44, FI- 00014 Helsinki, Finland. bjorn.kroger@helsinki.fi Author Pohle, Alexander 9C9B621D-7A77-41FF-8B63-DD21BEE10B56 Paläontologisches Institut und Museum, University of Zurich, Zurich, Switzerland. alexander.pohle@pim.uzh.ch text European Journal of Taxonomy 2021 2021-12-20 783 1 1 102 http://dx.doi.org/10.5852/ejt.2021.783.1601 journal article 2884 10.5852/ejt.2021.783.1601 aa9de9bf-dea4-4321-a51d-6c4f1f55032d 2118-9773 5793422 071EAD63-05ED-4D6C-AC45-8719E6D79E0B Cycloplectoceras hinlopense sp. nov. urn:lsid:zoobank.org:act: 17CC19A8-797C-4718-AE09-C6DEEF037258 Fig. 41C–D Diagnosis Strongly ribbed Cycloplectoceras with rapidly enlarging conch with WER of ca 3.7 and LER of ca 2, with adult size> 30 mm . Etymology From Hinlopen Strait, referring to the type region of this species. Type material Holotype Specimen FMNH-P30327 ; by monotypy. Type locality and horizon From Profilstranda section, Ny Friesland, Svalbard , bed PO 131, 128 m above base of Olenidsletta Member, Blackhillsian, Floian. Description Specimen FMNH-P30327 is a fragment of a phragmocone consisting of ca two whorls with a total diameter of 26 mm . The conch grows with a WER of 3.66 and a LER of 2. The whorl is 13 mm wide and high at a conch diameter of 26 mm and is slightly flattened on the lateral flanks and venter; a 0.3 mm deep imprint zone is present at the dorsum. The conch is strongly annulated with ribs than run obliquely transverse across the flanks and forming a deep and broad ventral lobe. Prominent growth lines or striae are present, ca 8 per one millimetre, and are parallel to the ribs. The siphuncular perforation has a diameter of 1.4 mm and is positioned at a distance of 1.3 mm from the venter (rSP = 0.1). The septal spacing is relatively narrow; where the conch is 22 mm in diameter the sutures have a distance of 2 mm apart over the venter. Remarks This specimen is assigned to Cycloplectoceras because it is a ribbed tarphycerid with rapidly enlarging whorls, both in whorl height and in whorl width. The conch cross section is nearly circular, similar as in known species of Cycloplectoceras . Pionoceras Ulrich et al. , 1942 is another annulated tarphycerid with high WER and rapid growth of the whorl width. Pionoceras , however, differs in having broadly subtrapezoidal whorl cross sections and a very broad venter. The fragment described above is, however, relatively small, and ontogenetic growth changes are frequent among tarphycerid species, and especially among species of Pionoceras . It is therefore possible that this specimen represents a fragment of a larger individual, which if fully preserved would exhibit an adult morphology with an aspect of Pionoceras . More material is required to fully document the ontogeny, and consequently to further support the generic assignment of this species. Cycloplectoceras hinlopense sp. nov. differs from C . miseri Ulrich, Foerste, Miller & Furnish, 1942 in being larger (the adult size of C . miseri is only 20 mm ). The other known species of Cycloplectoceras , C . funatum Ulrich, Foerste, Miller & Furnish, 1942 , has a smaller rate of increase in relative conch width (LER = ca 1.2, compare Ulrich et al. 1942 : pl. 6 fig. 7) and is less strongly annulated.