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

Discoceras alienum sp. nov. urn:lsid:zoobank.org:act: 6E931B16-8922-43E2-9558-DD1F36CE8A40 Figs 23, 26; Table 15 Diagnosis Species of the genus Discoceras with adult conch size of 55 mm; adapertural half of the body chamber slightly uncoiled; whorl profile in external volution weakly compressed (WWI = 0.77), barely imprinted dorsally (IZR close to zero or zero), and elliptic in shape; aperture extended with a ventral sinus; shell ornament of raised lirae, slightly unevenly spaced, slightly imbricated with fine lirae or growth lines in between. Etymology From the Latin ‘alienum’ (adj., neut.) = ‘foreign’, referring to the origin of the holotype from erratic boulders. Type material Holotype GERMANY – Brandenburg • Oderberg; Moldåan Regional Stage (early Katian Stage, Late Ordovician); Neben Coll.; illustrated in Fig. 26; MB.C.32327. Description Holotype MB.C.32327 is an adult conch, 55 mm in diameter, with a partly uncoiled body chamber (Fig. 26). The conch is discoidal (CWI = 0.29) and subevolute (UWI = 0.38). In the last 90 degrees of the conch, the coiling rate (WER wh) decreases from 2.81 to 2.61, and the whorl profile becomes less compressed (WWI increases from 0.68 to 0.77); it is elliptic in shape. The whorls are weakly imprinted dorsally or not imprinted (IZR close to zero). The body chamber is preserved over 148 degrees, with its adapertural half uncoiled from the preceding whorl; the aperture extends into a small ventral sinus. The relative cameral length (RCL) in the last half whorl is 0.20. The shell surface has raised lirae (also visible on the internal mould), which are slightly unevenly spaced and slightly imbricated; fine lirae or growth lines are present between the coarser elements. Remarks Discoceras alienum sp. nov. differs from other species of the genus by its comparatively small, adaperturally only weakly uncoiled, and extremely discoidal conch with a compressed, elliptic whorl profile. Discoceras alienum sp. nov. closely resembles D. sovaki sp. nov., but the former is smaller (55 mm vs 70 mm) and has a less strongly uncoiled body chamber. Additionally, D. alienum has a higher expansion rate (WER wh = 2.61 vs 2.42 at dm = 55 mm), a more compressed whorl profile (WWI = 0.77 vs 0.86 at dm = 55 mm), and a finer shell ornamentation (raised lirae vs regularly spaced sharp lirae or thin annuli). Discoceras vasalemmense differs from D. alienum sp. nov. in having a heart-shaped whorl profile and a coarser shell ornamentation, which consists of strongly crenulated and irregularly spaced transverse elements (Kröger & Aubrechtová 2018). Geographic and stratigraphic occurrence Northern Germany; early Katian Stage, Late Ordovician.