Liroceras vermis, 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 : 178-179

Liroceras vermis sp. nov.

urn:lsid:zoobank.org:act:AE14647B-7469-4BFC-91E3-99F7A8791CDD

Figs 15–16 ; Table 6

Diagnosis

Species of Liroceras with thickly pachyconic, subinvolute conch (ww/dm ~0.82; uw/dm ~ 0.20), whorl profile moderately depressed (ww/wh ~1.75) with broadly rounded venter and broadly rounded umbilical margin. Coiling rate very high (WER ~2.85), whorls very weakly embracing (IZR ~ 0.15). Suture line nearly straight.

Etymology

From the Latin ‘ vermis ’, meaning ‘maggot’, because of the appearance of the holotype.

Material examined

Holotype MOROCCO • Anti-Atlas, north of Gara el Itima , 35 km east-northeast of Taouz ; basal Hamou-Rhanem Formation; Ebbighausen & Korn 2004 Coll.; illustrated in Fig. 15C ; MB.C.31295.1 .

Paratypes MOROCCO • 4 specimens; same collection data as for holotype; Ebbighausen & Korn 2004 Coll.; MB.C.31295.2 – 31295.5 .

Description

Specimen MB.C.31295.1 ( Fig. 15C ) was chosen as the holotype because it is the only one that shows traces of the shell ornament. It is, with 34 mm conch diameter, thickly pachyconic and subinvolute (ww/ dm ~ 0.82; uw/dm ~ 0.21) with a strongly depressed, reniform whorl profile (ww/wh ~1.77), a very small whorl overlap zone (IZR ~0.12) and a very high coiling rate (WER ~2.85). The whorl profile has a broadly parabolic outline. The venter is broadly arched; the conch is widest at the umbilical margin from where the broadly rounded flanks converge towards the venter. The umbilical margin is continuously rounded and the umbilical wall is convex. The suture line extends almost straight across the umbilical wall, flanks and venter. Shell remains on the umbilical wall show that four fine and sharp, wide-standing spiral lines are located on the outer portion of the umbilical wall. These spirals are entirely formed by the shell; they are not visible on the internal mould.

Paratype MB.C.31295.3 ( Fig. 15B ) is also a desert-corroded specimen, with 42 mm conch diameter, of which the last quarter of a whorl belongs to the body chamber. It has a geometry very similar to that of the holotype (ww/dm ~0.81; uw/dm ~ 0.20; ww/wh ~1.76; WER ~ 2.89; IZR ~0.11) The suture line extends almost straight across the umbilical wall, flanks and venter ( Fig. 16A ).

The second paratype, MB.C.31295.2 ( Fig. 15A ), has about 49 mm in conch diameter and is less strongly corroded than the other two specimens. It is an internal mould that appears to be completely smooth without any traces of ornament. Its conch proportions are almost exactly corresponding to those of the other two specimens.

The three specimens show that ontogenetic changes of the conch geometry and variation between the specimens is low ( Fig. 16B–D ), at least in the examined size-range. Between 20 and 49 mm in conch diameter, the ww/dm ratio ranges between 0.81 and 0.88, the uw/dm ratio between 0.20 and 0.25 and the whorl expansion rate between 2.83 and 2.89.

Remarks

Liroceras vermis sp. nov. belongs to the thickly pachyconic to globular species of the genus like L. excentricum and L. lunense , while the other species possess more compressed conchs. The new species differs from L. lunense and L. concentricus in the wider umbilicus (uw/dm ~ 0.20 in L. vermis and ~ 0.12 in the other two species) and from L. praelunense in the more slender conch (ww/dm ~ 0.82 in contrast to ~ 0.92).

Figures

Fig. 15. Liroceras vermis sp. nov. from N of Gara el Itima (all Ebbighausen & Korn 2004 Coll.). A. Paratype MB.C.31295.2; dorsal and lateral views. B. Paratype MB.C.31295.3; dorsal and lateral views. C. Holotype MB.C.31295.1; dorsal and lateral views. Scale bar units =1 mm.

Fig. 16. Liroceras vermis sp. nov. from N of Gara el Itima. A. Suture line of paratype MB.C.31295.3 (Ebbighausen & Korn 2004 Coll.), at dm =32.0 mm, ww =29.5 mm, wh =15.0 mm. B–D. Ontogenetic trajectories of the cardinal conch parameters. Scale bar units= 1 mm.