Planetoceras transforme, Korn & Miao & Bockwinkel, 2022

Korn, Dieter, Miao, Luyi & Bockwinkel, Jürgen, 2022, The nautiloids from the Early Carboniferous Dalle à Merocanites of Timimoun, western Algeria, European Journal of Taxonomy 789, pp. 104-129 : 125-127

Planetoceras transforme sp. nov.

urn:lsid:zoobank.org:act:CDD3B745-0819-4EA2-8728-D0CAB8CE609B

Fig. 14 ; Table 9

Diagnosis

Species of Planetoceras with moderately depressed, rounded-pentagonal whorl profile (ww/wh> 2.00), venter slightly flattened, ventrolateral shoulder broadly rounded. Umbilical margin changes

from subangular to rounded, umbilical wall steep, changing from flattened to rounded. Whorls slightly embracing.

Etymology

After the Latin ‘ transforme ’, meaning ‘changing’, because of the rapid early ontogenetic change in morphology.

Type material

Holotype ALGERIA • Gourara , Sebkha de Timimoun 14.5 km west-southwest of Timimoun; “Dalle à Merocanites ” (Tournaisian-Viséan boundary interval); illustrated in Fig. 14 ; MB.C.30386 .

Description

Holotype MB.C.30386 consists of the first whorl with a diameter of about 28 mm ( Fig. 14A ) and a fragment of the second whorl making a total diameter of 44 mm ( Fig. 14B ). The conch is stout and has a subtrapezoidal whorl profile at 28 mm in diameter and an angular umbilical edge raised by a sharp keel. A vertical, flattened umbilical wall extends from here on one side and a converging flank on the other. At a short distance from the umbilical margin there is a pronounced but rounded ventrolateral shoulder. On the broad, slightly flattened venter there is a shallow longitudinal furrow next to the ventrolateral shoulder. Half a whorl before, at about 16 mm in diameter, the whorl profile is oval and depressed; at this diameter four longitudinal ridges are present. Of these, the innermost one becomes the ridge on the umbilical margin during the next half whorl, and the second one becomes the ridge at the inside of the ventrolateral shoulder. The third and fourth ridges become weaker and disappear on the next half whorl. The suture line extends almost straight across flanks and venter. The fragment of the larger whorl shows that the umbilical margin became rounded at 44 mm conch diameter ( Fig. 14B ).

Remarks

Planetoceras transforme sp. nov. differs from the other species of the genus in the very broad whorl profile (ww/wh> 2.00), which has a value of about 1.60 in other species such as P. destrictum sp. nov. and P. globatum ( Histon 1999) .

Figures

Fig. 14. Planetoceras transforme sp. nov., holotype MB.C.30386. A. Photograph of the inner whorl. B. Whorl profile of a larger phragmocone segment. Scale bar units = 1 mm.