Discoceras sovaki Aubrechtová, Korn & Kröger, 2026, sp. nov.

Discoceras sovaki sp. nov. urn:lsid:zoobank.org:act: 4A540D1B-F7B7-4638-827F-336D8CD3EAB0 Figs 23, 25; Table 14 Rectanguloceras (Discoceras) danckelmanni – Neben & Krueger 1973: pl. 65 figs 3–4. Diagnosis Species of the genus Discoceras with adult conch size of ~ 70 mm, of which the coiled part is ~ 55 mm in diameter; body chamber uncoils from about half of its length onward; whorl profile in external volution weakly compressed (WWI between 0.78 and 0.86), barely imprinted dorsally (IZR close to zero or zero), and elliptic in shape, slightly ventrally flattened from the base of the body chamber; shell ornament of sharp, raised lirae or thin annuli, evenly spaced, slightly imbricated with fine lirae or growth lines in between them. Etymology In honour of the late Jan Sovák (1953–2025), Czech painter renowned for vivid reconstructions of prehistoric life, including early Palaeozoic cephalopods. Type material Holotype GERMANY – Brandenburg • Prenzlau; Moldåan Regional Stage (early Katian Stage, Late Ordovician); Neben Coll.; illustrated in Fig. 25; MB.C.32326. Description Holotype MB.C.32326 is a conch of an adult individual with an adorally incomplete, uncoiled body chamber (Fig. 25). The maximum diameter of the conch is 70 mm, with the coiled part accounting for up to 55 mm. In the last 0.75 whorls, the conch is discoidal (CWI decreases from 0.36 to 0.31) and subevolute (UWI increases up to 0.39). The coiling rate (WER wh) decreases from 2.98 to 2.42. The whorl profile is weakly compressed (WWI between 0.78 and 0.86), very weakly imprinted dorsally or not imprinted (IZR close to zero or zero) and elliptic in shape. From the rear part of the body chamber, the profile is slightly flattened ventrally. The suture line has a low lateral lobe and an external saddle. The body chamber is preserved over 115 degrees and becomes uncoiled from the previous whorl after ~70 degrees, with no indication of proximity to the aperture. In the outer volution, the relative cameral length (RCL) is 0.14. The shell ornament consists of sharp, raised lirae or thin annuli, which are also visible on the internal mould. The ornament elements are evenly spaced, slightly imbricated, and have fine lirae or growth lines between them. Remarks Discoceras sovaki sp. nov. is distinguished from other species of the genus by its comparatively small, extremely discoidal, adaperturally uncoiled, and sharply ornamented conch. The holotype of D. sovaki sp. nov. is most similar to the holotype of D. alienum sp. nov., but differs in its larger adult size (70 mm vs 50 mm) and in having a body chamber that is much more strongly uncoiled from the previous whorls. Additionally, D. sovaki has a lower coiling rate (WER wh = 2.42 vs 2.61 at a diameter of 55 mm), a less compressed whorl profile (WWI = 0.86 vs 0.77 at dm = 55 mm), and a coarser shell ornamentation (sharp lirae or thin annuli vs fine lirae). The conch ratios of D. sovaki sp. nov. are also similar to those of the late Sandbian D. vasalemmense from Estonia. However, in late growth stages, the latter species exhibits a heart-shaped whorl profile (where the conch narrows ventrally) and an even coarser ornamentation with strongly crenulated and irregularly spaced transverse elements (Kröger & Aubrechtová 2018). Geographic and stratigraphic occurrence Northern Germany; early Katian Stage, Late Ordovician.