Liroceras karaouii, Korn & Klug, 2023

Korn, Dieter & Klug, Christian, 2023, Early Carboniferous coiled nautiloids from the Anti-Atlas (Morocco), European Journal of Taxonomy 885, pp. 156-194 : 180-181

Liroceras karaouii sp. nov.

urn:lsid:zoobank.org:act:2EDCD119-FDE9-426A-9547-A89E8AA520F4

Fig. 17 ; Table 7

Diagnosis

Species of Liroceras with thickly pachyconic, subinvolute conch (ww/dm ~0.75; uw/dm ~0.25), whorl profile moderately depressed (ww/wh ~ 1.65) with broadly rounded venter and subangular umbilical margin. Coiling rate very high (WER ~ 2.65), whorls very weakly embracing (IZR ~0.17). Suture line nearly straight.

Etymology

Named after Driss Karaoui (Hassilabied), the collector of the specimen.

Material examined

Holotype MOROCCO • Anti-Atlas, region south-west of Rissani ; basal Mougoui Ayoun Formation; Karaoui Coll.; illustrated in Fig. 17 ; PIMUZ 39515 .

Description

Holotype PIMUZ 39515 is a corroded, desert-polished specimen with a phragmocone diameter of about 46 mm ( Fig. 17 ). It is fully septate and has about 22 chambers in the last volution. It is, at 46 mm in conch diameter, thickly pachyconic and subinvolute (ww/dm=0.77; uw/dm=0.25) with a strongly depressed, reniform whorl profile (ww/wh=1.65), a very small whorl overlap zone (IZR= 0.17) and a very high coiling rate (WER ~ 2.65). The whorl profile is crescent-shaped and widest at the subangular umbilical margin. The umbilical wall is flattened and slightly oblique. The suture line extends nearly linearly across the flanks and venter.

Remarks

Liroceras karaouii sp. nov. differs from L. vermis sp. nov. in the subangular umbilical margin and in the slightly wider umbilicus (uw/dm ~ 0.25 in L. karaouii but only uw/dm ~ 0.20 in L. vermis ). This shape of the umbilicus is also the most important distinguishing character from the other species of the genus. The pronounced umbilical margin in L. karaouii can be seen as a plesiomorphic character, which transforms from the possible evolutionary lineage from Bistrialites to Liroceras .

Figures

Fig. 17. Liroceras karaouii sp. nov.; dorsal projection, dorsal and lateral views of holotype PIMUZ 39515 (Karaoui Coll.) from the region south-east of Rissani; reconstruction of apertural view, dorsal and lateral views. Scale bar units =1 mm.

Tables

Table 7. Conch dimensions (in mm) and ratios of the holotype of Liroceras karaouii sp. nov.

specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZR
PIMUZ 39515	45.9	35.5	21.5	11.4	17.8	0.77	1.65	0.25	2.67	0.17