Xenoglyphioceras eidos, Korn, 2025

Xenoglyphioceras eidos gen. et sp. nov.

urn:lsid:zoobank.org:act:9E318F16-BB75-4DCA-B078-51384494F14B

Figs 3–4 View Fig View Fig ; Table 1 View Table 1

Diagnosis

Species of Xenoglyphioceras gen. nov. with a conch reaching a diameter of 80 mm. Conch thickly discoidal and involute at 30 mm diameter (ww/dm ~ 0.55; uw/dm ~ 0.10) and thinly discoidal and subinvolute at 60 mm diameter (ww/dm ~ 0.40; uw/dm ~ 0.20). Shell ornament with dense spiral lines and biconvex growth lines. Adult stage with constrictions that bend forward in the ventrolateral area to continue in longitudinal grooves. Suture line with a moderately wide external lobe (0.60–0.65 of the external lobe depth) and a moderately low median saddle (0.35–0.40 of the external lobe depth).

Etymology

From the Greek ‘ τὸ εἶΔΟΣ ’ (noun in apposition) = ‘the beauty’; because of the combination of morphological characters.

Type material

Holotype

MOROCCO – Anti-Atlas • Gara el Itima , near locality GI-J; 31°02.747′ N, 3°42.429′ W; Zrigat Formation, horizon GI-1 (Late Viséan); 2007; Korn et al. leg.; MB.C.32198.1 ; illustrated in Fig. 3A View Fig .

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Paratypes

MOROCCO – Anti-Atlas • 11 specs; same data as for the holotype; MB.C.32198.2 to MB.C.32198.12 .

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Description

Holotype MB.C.32198.1 is an almost completely chambered internal mould with a conch diameter of 61 mm ( Fig. 3A View Fig ). Less than a quarter of a volution belongs to the incomplete body chamber. The conch is thinly discoidal and subinvolute (ww/dm = 0.38; uw/dm = 0.20). It should be noted that the umbilicus opens rather clearly on the last volution of the phragmocone. The whorl profile is weakly compressed (ww/wh = 0.93) with a uniformly rounded venter that merges into the slightly convex, weakly convergent flanks via a broadly rounded ventrolateral shoulder. The umbilical margin is subangular and separates the flank from the flattened, almost vertical umbilical wall. The coiling rate is very low (WER = 1.48).

The surface of the internal mould appears to be completely smooth, although traces of very fine spiral lines can be seen in some small areas. The last volution shows five shallow constrictions, which are arranged at somewhat irregular distances from one another. They have a weakly biconvex course with very low dorsolateral and ventrolateral projections and a very deep ventral sinus. The last of the constrictions differs in its course from the others in that the ventrolateral projection is very prominent. It cannot be said if the constrictions and grooves were also present on the shell surface or if the just represent internal shell thickenings.

The suture line has a V-shaped external lobe with clearly sinuous flanks; the median saddle reaches a height of 0.36 the depth of the external lobe. The ventrolateral saddle is somewhat asymmetrical and bluntly rounded; the adventitious lobe is almost symmetrical with convex flanks ( Fig. 4A View Fig ).

Paratype MB.C.32198.2 is a completely chambered internal mould specimen with a conch diameter of 38 mm ( Fig. 3B View Fig ). The conch is thickly discoidal and involute (ww/dm = 0.49; uw/dm = 0.13). The umbilicus opens only slowly on the last volution of the phragmocone. The whorl profile is weakly depressed (ww/wh = 1.06) with a uniformly rounded venter that merges into the slightly convex, weakly convergent flanks via a broadly rounded ventrolateral shoulder. The umbilical margin is narrowly rounded. The last volution has three shallow constrictions, which are very weakly biconvex course with very low dorsolateral and ventrolateral projections and a deep, semicircular ventral sinus. The suture line ( Fig. 4B View Fig ) is similar to that of the holotype.

Paratype MB.C.32198.3 is a body chamber fragment of an approximately 75 mm large specimen ( Fig. 3D View Fig ). At a shell diameter of 55 mm, it already displays distinctly pronounced ventrolateral grooves, accompanied by clearly biconvex radial constrictions. Between these constrictions, very faint plications can be recognised on the flanks. As with the holotype, it cannot be determined whether the constrictions and ventrolateral grooves seen on the internal mould are also present on the shell surface, or if they represent internal thickenings of the shell.

The paratypes MB.C.32198.4 ( Fig. 3C View Fig ) and MB.C.32198.5, like paratype MB.C.32198.3, are fragments of the adult body chamber. Both show the characteristic constrictions and grooves. Both exhibit the impression of the shell of the penultimate whorl in the inner part of the body chamber. It is evident that the primary element of the shell ornamentation consists of very fine, closely spaced spiral lines. The shell surface of the penultimate whorl shows no constrictions or grooves.

Remarks

Xenoglyphioceras eidos gen. et sp. nov. resembles species of Beyrichoceras in the late juvenile and preadult ontogenetic stages but differs significantly in the adult stage due to the prominent constrictions and ventrolateral grooves.