Rineceras tenerum Korn & Bockwinkel 2022, sp. nov.
Creators: name: Korn, Dieter
name: Bockwinkel, Jürgen
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Nautilida
Trigonoceratidae
Rineceras
Rineceras tenerum

description: 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.
description: Published as part of Korn, Dieter & Bockwinkel, Jürgen, 2022, Early Carboniferous nautiloids from the Central Sahara, southern Algeria, pp. 67-108 in European Journal of Taxonomy 831 on pages 72-74, DOI: 10.5852/ejt.2022.831.1871, http://zenodo.org/record/6885198