Svalbardocreas skua Kröger & Pohle 2021, gen. et sp. nov.

Svalbardocreas skua gen. et sp. nov.

urn:lsid:zoobank.org:act: 9385D872-8656-4B53-9CA8-05F7575BEB6F

Figs 16B, 19C, 20–21, 22A–D, 23B, D, F

Diagnosis

Slightly curved longicones with circular conch cross section; shell ornamented with shallow, irregularly spaced undulations that are more pronounced in later growth stages and with fine, irregularly spaced, directly transverse growth lines or bands; thin, nearly marginal siphuncle with relative siphuncle diameter of ca 0.16 of corresponding conch cross section, siphuncle positioned at concave side of conch curvature; septal necks orthochoanitic; connecting ring relatively thick with slightly concave segments, weak hyposeptal and episeptal deposits occur.

Etymology

Referring to Stercorarius skua (Brünnich, 1764), a bird which was a common companion during our field work at Profilstranda, Ny Friesland.

Type material

Holotype Specimen FMNH-P30272.

Paratypes Nine specimens from type locality, one from bed PO 123 (FMNH-P30271), eight from bed PO 123.3 (FMNH-P30263, P30264, P30273, P30275 to P30277, P30408, P30471), 120–120.3 m above the base of the Olenidsletta Member, V2 a trilobite zone, Blackhillsian, Floian.

Type locality and horizon

From Profilstranda section, adjacent to Hinlopenstretet, Spitsbergen, bed PO 123.3, 120.3 m above the base of the Olenidsletta Member, V 2a trilobite zone, Blackhillsian, Floian.

Description

The conchs are slightly curved with angle of expansion of <ca 7° (mean angle of expansion = 4.8°, 1 st –3 rd quantile: 3.3–4.8; n = 7), which decreases with conch size from ca 11° to 5° (Figs 20, 22A–D). The conch cross section is invariantly circular.

The conch surface is ornamented with fine growth lines or growth bands (Fig. 29C) and annulations, which are slightly obliquely transverse, and shifted toward the aperture at the antisiphuncular side.

The sutures are slightly obliquely transverse and shifted toward the aperture at the antisiphuncular side. The relative chamber length (rCL) decreases with increasing conch cross section (Fig. 21), ranging from ca 0.25 to more than 0.3.

The siphuncle is marginally positioned, very slightly removed from the conch margin (Fig. 23B), at the concave side of the conch curvature with a mean rSD of 0.16 (1 st –3 rd quantile: 0.13–0.19; n = 4). The septal necks are orthochoanitic. The connecting ring is moderately thick and forms slightly concave siphuncular segments (Fig. 23F). Weak epi-, and hyposeptal deposits occur in the extreme apical part of specimen FMNH-P30274 at a conch height of ca <2.8 mm. In one specimen part of the body chamber is preserved (specimen FMNH-P30276); the body chamber is> 26 mm long and the conch diameter at the position of the last septum is 5.5 mm.

Comparison

See above, under Svalbardoceras sterna gen. et sp. nov.