Rineceras tenerum, 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 : 72-74

Rineceras tenerum sp. nov.

urn:lsid:zoobank.org:act:94410544-F569-471D-A008-97466EB83BBF

Figs 4–5 , Table 1

Diagnosis

Species of Rineceras with weakly depressed, rounded-trapezoidal whorl profile (ww/wh ~1.45), venter slightly flattened, ventrolateral shoulder broadly rounded. Whorls not embracing. Ornament with a few spiral lines on the flank and the venter.

Etymology

From the Latin ‘ tenerum ’, meaning ‘tender’ and referring to the comparatively delicate spiral lines.

Type material

Holotype ALGERIA • Mouydir , south of Oued Temertasset (locality MOU-Z); Argiles de Teguentour (Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian); Korn et al. 2002 Coll.; illustrated in Fig. 4A–B ; MB.C.30440.1 .

Paratypes ALGERIA • 1 specimen; Mouydir , south of Oued Temertasset (locality MOU-E07); Argiles de Teguentour (Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian); Korn et al. 2002Coll.; illustrated in Fig. 4C ; MB.C.30441 • 8 specimens; Mouydir , south of Oued Temertasset (localities MOU-Z, MOU-C5, MOU-B1, MOU-D1); Argiles de Teguentour (Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian); Korn et al. 2002 Coll.; MB.C.30440.2 , MB.C.30442 , MB.C.30443.1–MB.C.30443.2 , MB.C.30444.1–MB.C.30444.4 .

Description

Holotype MB.C.30440.1 is a haematitic internal mould consisting of two fully chambered segments; however, some chambers between the two segments are missing ( Fig. 4A–B ). The total diameter is about 49 mm. At this diameter, the whorl profile is rounded-triangular with a somewhat flattened venter and continuously rounded dorsum. There is no overlap upon the previous whorl ( Fig. 5A ). On the flanks and the outer part of the venter, there are twelve spiral lines on each side. The suture line shows a low amplitude; there is a wide, shallow external lobe and a low, tightly rounded ventrolateral saddle. On the flanks and dorsum the suture line is almost straight ( Fig. 5B ).

The segment of the younger stage ( Fig. 4B ) shows the conch dimensions and proportions better. The conch is evolute at 28 mm diameter (uw/dm =0.48). The whorl profile is similar to the large segment, but the venter is slightly more flattened and the ventrolateral shoulder is more pronounced with a very shallow submarginal ventral groove ( Fig. 5C ). From the margin of the venter and on the flank, there are about 12 spiral lines. However, it can be seen that the number of spiral lines decreases during ontogeny; over a distance of 180 degrees, the initially coarse spiral lines in the submarginal area of the venter become weaker gradually. The siphuncle has a position slightly off centre on the ventral side. The suture line shows a broad and shallow external lobe and a very shallow lateral lobe ( Fig. 5D ).

Paratype MB.C.30441 closely resembles the holotype but has a slightly more pronounced ventrolateral shoulder ( Fig. 4C ). The large unfigured paratype MB.C.30442 has, at a whorl height of 21 mm, a whorl profile almost identical to the holotype; it also possesses twelve coarse spiral lines on the flanks and the outer part of the venter.

Remarks

The species of the genus Rineceras can be divided into different groups according to various aspects: general conch shape (whorls detached or embracing), whorl profile (depressed oval, rounded-triangular or trapezoidal), formation of the ventrolateral shoulder (rounded or angular), spiral ornament (spirals equally strong or differently strong) etc.

Rineceras tenerum sp. nov. differs from all other species of the genus by the combination of rather weak spiral lines that are restricted to the flank, the non-embracing whorls, and the whorl profile with a rounded-triangular outline.

Figures

Fig. 4. Rineceras tenerum sp. nov. from Oued Temertasset (all Korn et al. 2002 Coll.). A. Holotype MB.C.30440.1 (larger segment). B. Holotype MB.C.30440.1 (smaller segment). C. Paratype MB.C.30441. Scale bar units =1 mm.

Fig. 5. Rineceras tenerum sp. nov., holotype MB.C.30440.1 (Korn et al. 2002 Coll.) from Oued Temertasset. A. Whorl profile of the larger segment. B. Suture line, at ww =19.7 mm, wh= 13.7 mm. C. Whorl profile of the smaller segment. D. Suture line, at dm =26.3 mm, ww =11.3 mm, wh=8.0 mm. Scale bar units =1 mm.

Tables

Table 1. Conch dimensions (in mm) and ratios of Rineceras tenerum sp. nov.

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZW
MB.C.30440.1	48.8	21.4	14.7	23.5	14.7	0.44	1.45	0.48	2.05	0.00
MB.C.30440.1	27.7	12.7	9.4	13.3	9.4	0.46	1.35	0.48	2.29	0.00
MB.C.30442	–	32.5	21.9	–	–	–	1.48	–	–	–
MB.C.30441	–	15.6	10.9	–	–	–	1.49	–	–	–