Vestinautilus bicristatus, Korn & Bockwinkel, 2022

Korn, Dieter & Bockwinkel, Jürgen, 2022, Early Carboniferous nautiloids from the Central Sahara, southern Algeria, European Journal of Taxonomy 831, pp. 67-108 : 91-92

Vestinautilus bicristatus sp. nov.

urn:lsid:zoobank.org:act:69CABBA5-6CDA-4264-B156-0FB2321AEDD5

Figs 20–21 , Table 11

Diagnosis

Species of Vestinautilus with strongly depressed, rounded-trapezoidal whorl profile (ww/wh ~ 2.10), venter up to 30 mm conch diameter broadly arched with two shallow submarginal grooves, which disappear in the adult stage. Ventrolateral shoulder defined by a subangular margin; one sharp ridge is located on the umbilical wall near the ventrolateral shoulder. Whorls weakly embracing, coiling very high (WER ~2.55). Ornament with delicate growth lines.

Etymology

From the Latin ‘ crista ’, meaning ‘crest’ and referring to the two lateral longitudinal ridges.

Type material

Holotype ALGERIA • Mouydir , south of Oued Temertasset (locality MOU-C1); Argiles de Teguentour (Helicocyclus-Ouaoufilalites Assemblage; early late Tournaisian); Wendt et al. Coll.; illustrated in Fig. 20 ; MB.C.30473 .

Paratypes ALGERIA • 3 specimens; Mouydir , south of Oued Temertasset (locality MOU-C1); Argiles de Teguentour (Helicocyclus-Ouaoufilalites Assemblage; early late Tournaisian); Korn et al. 2002 Coll.; illustrated in Fig. 21 ; MB.C.30474.1 – MB.C.30474.3 .

Description

Holotype MB.C.30473 is a desert-polished specimen with a diameter of 38 mm, showing the conch shape and small areas of ornament ( Fig. 20 ). The conch is broadly cylindrical and subevolute (ww/dm = 0.84; uw/dm =0.37) with a very high coiling rate (WER =2.57). The whorl profile is strongly depressed (ww/wh =2.13) and shows a flattened venter, which possesses two submarginal external grooves at size stages between 17 and 35 mm diameter. These weaken considerably thereafter and are only visible as shallow longitudinal depressions at the maximum diameter of the specimen. The ventrolateral shoulder is distinguished by three edges, of which the two inner ones are strengthened by longitudinal ridges. Only small areas of shell ornament are visible; these show very fine growth lines on the venter with a deep external sinus.

Three paratypes in fragmentary preservation are available. They are larger specimens with whorl widths between 49 and 80 mm, thus belonged to conchs with 60 to 90 mm diameter. Two of them (MB.C.30474.2 and MB.C.30474.3; Fig. 21B–C ) show the imprint of the preceding whorl with sublateral longitudinal grooves in the dorsal region; in paratype MB.C.30474.3 the edges of the ventrolateral shoulder are also still visible. Both have a broadly rounded venter. The largest paratype MB.C.30474.1 shows a shallow, broad depression in the middle of the venter at its largest diameter ( Fig. 21A ).

Paratype MB.C.30474.3 shows the suture line with a broad and shallow external lobe and a narrow and shallow lateral lobe, which has a position on the umbilical wall ( Fig. 21C ). The siphuncle has a slightly subcentral position towards the venter.

Remarks

Vestinautilus bicristatus sp. nov. belongs to the species of the genus that possess a very broad whorl profile (ww/wh> 2.00) and an ornament with only a few spiral ridges. In this respect, V. cariniferus , V. paucicarinatus , V. pinguis and V. semiplicatus are similar, but these four species have a concave venter at least at times in ontogeny ( Sowerby 1825; de Koninck 1844; Foord 1891, 1900). The most similar V. bicristatus sp. nov. is the species V. padus , which shows the same conch dimensions, but differs in the lack of the submarginal ventral grooves ( Korn et al. 2022).

Figures

Fig. 20. Vestinautilus bicristatus sp. nov., holotype MB.C.30473 (Wendt & Kaufmann Coll.) from Oued Temertasset. Scale bar units = 1 mm.

Fig. 21. Vestinautilus bicristatus sp. nov. from Oued Temertasset (all Korn et al. 2002 Coll.). A. Paratype MB.C.30474.1. B. Paratype MB.C.30474.2. C. Paratype MB.C.30474.3. Scale bar units =1 mm.

Tables

Table 11. Conch dimensions (in mm) and ratios of Vestinautilus bicristatus sp. nov.

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZW
MB.C.30473	38.0	31.9	14.9	14.0	14.3	0.84	2.13	0.37	2.57	0.04