Solenochilus pohlei, 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 : 186-188

Solenochilus pohlei sp. nov.

urn:lsid:zoobank.org:act:7C35A00D-0C45-43E5-A3F0-B7A2811164D6

Fig. 20 ; Table 10

Diagnosis

Species of Solenochilus with thickly pachyconic, involute conch (ww/dm ~ 0.80; uw/dm ~0.15), whorl profile weakly compressed (ww/wh ~ 1.40) with broadly rounded venter and rounded umbilical margin. Development of a distinct ridge in the centre of the umbilical wall. Coiling rate extremely high (WER higher than 5.50), whorls not embracing. Suture line nearly straight.

Etymology

Named after Alexander Pohle, in honour of his studies on Palaeozoic nautiloids.

Material examined

Holotype MOROCCO • Anti-Atlas, region south-east of Rissani ; basal Mougoui Ayoun Formation; Karaoui Coll.; illustrated in Fig. 20B ; PIMUZ 39513 .

Paratype MOROCCO • 1 specimen; same collection data as for holotype; Karaoui Coll.; PIMUZ 39508 .

Description

Holotype PIMUZ 39513 is an almost completely septate fragment of a conch with a constructed diameter of about 78 mm ( Fig. 20A–B ). It has an oval, slightly depressed whorl profile (ww/wh ~1.40) with a broadly rounded area consisting of flanks and venter.The whorl profile is widest near the rounded umbilical margin. The umbilical wall shows a rapid change from a simple convex shape to a biconcave shape in the segment of the last third volution. This is produced by the rapid protrusion of a narrowly rounded ridge, which would probably develop into a longer umbilical spine at a later ontogenetic stage. The dorsum is flattened and slightly incurved, but there is no sign of a preceding whorl; the coiling rate is extremely high (WER ~ 5.60). The specimen shows an oval, slightly depressed whorl profile in the penultimate half volution ( Fig. 20A ). The specimen does not provide evidence of the size of the protoconch. Areas of the shell surface are preserved on the umbilical wall and the inner flanks, although heavily corroded. They show fine growth lines that are already strongly curved backwards from the umbilical ridge, show a weak projection on the umbilical margin and extend backwards on the inner flank.

Paratype PIMUZ 39508 is also corroded and measures 73 mm in diameter ( Fig. 20C ). It exposes two thirds of the last whorl including parts of the body chamber. This specimen shows no whorl overlap and an extreme whorl expansion rate of over 6.00. The umbilicus is opened (uw/dm =0.16); the umbilicus is oblique and convex. It displays the characteristic bulge, which rises from the umbilical seam and climbs toward the umbilical shoulder over the last half volution. The terminal spine is not preserved, since the terminal aperture is missing. It shows the nearly straight suture line. It shows that the siphuncle has a nearly ventral position but does not affect the suture line.

Remarks

Solenochilus pohlei sp. nov. differs from S. lucynae sp. nov. in the presence of a ridge in the centre of the umbilical wall. Furthermore, S. lucynae has embracing whorls, while in S. pohlei the whorls, at least at a conch diameter of about 78 mm, do not show a concave whorl zone.

A very similar specimen was illustrated by Sturgeon & Miller (1948) as Solenochilus greenensis ; however, it has a Moscovian age. According to the authors, is has a “relatively narrow” impressed zone and differs thus from S. pohlei sp. nov., without an impressed zone.

Figures

Fig. 20. Solenochilus pohlei sp. nov. from the region south-east of Rissani, both Karaoui Coll. A. Holotype PIMUZ 39513; cross section, partly reconstructed. B. Holotype PIMUZ 39513; lateral and ventral views. C. Paratype PIMUZ 39508; lateral and ventral views. Scale bar units =1 mm.