Cymaclymenia formosa, Klein & Korn, 2014

Klein, C. & Korn, D., 2014, A morphometric approach to conch ontogeny of Cymaclymenia and related genera (Ammonoidea, Late Devonian), Fossil Record 17 (1), pp. 1-32 : 16

publication ID	https://doi.org/ 10.5194/fr-17-1-2014
DOI	https://doi.org/10.5281/zenodo.10997810
persistent identifier	https://treatment.plazi.org/id/4D1287FB-CB3F-FFDA-FF98-34A6FC6BFAAC
treatment provided by	Felipe
scientific name	Cymaclymenia formosa
status	sp. nov.

Treatment

Cymaclymenia formosa View in CoL n. sp.

Figures 15 View Figure 15 and 16 View Figure 16

1999 Cymaclymenia striata . – Korn, p. 170, pl. 4, fig. 1.

1999 Cymaclymenia costellata . – Korn, p. 170, pl. 4, fig. 2.

2002 Cymaclymenia involvens . – Becker et al., p. 165.

Derivation of name: After Lat. formosus, -a, -um (adj.) = pretty; because of the delicate ornament of the species.

Holotype: Specimen MB.C.22609.1 (Korn 1995 Coll.); illustrated here in Fig. 15a View Figure 15 .

Type locality and horizon: Erfoud (Anti-Atlas), immediately east of the Muslim cemetery on the eastern side of the Ziz Valley; bed 49– 50 of Korn (1999), Parawocklumeria paradoxa Assemblage (late Famennian).

Material: 267 specimens with a maximum conch diameter of 60 mm.

Diagnosis: Species of Cymaclymenia with thinly discoidal conch in the adult stage (ww / dm = 0.30–0.35); whorl cross section weakly compressed (ww / wh = 0.65). Conch shape in the intermediate stage (10 mm dm) thinly discoidal and subevolute (ww / dm = 0.35; uw / dm = 0.30–0.35). Umbilical wall steep in the adult stage, flanks weakly converging, venter rounded. Ornament with fine biconvex growth lines, without riblets.

Discussion: The new species closely resembles C. striata ( Münster, 1832) , which has a similar conch geometry and ornament. C. semistriata Münster (1832) is another similar and possibly separate species; it shows strong constrictions on the internal mould, which appear to be absent in C. striata . C. striata is characterised by very coarse, lamellose growth lines, which are arranged in equal distances of about 0.5 mm on the outer flanks (topotype specimen MB.C.4173 from Schübelhammer) ( Fig. 17 View Figure 17 ). In contrast the growth lines are much finer in C. formosa and stand in distances of about 0.25 mm. The steinkern constrictions, characteristic of C. semistriata , are absent in C. formosa .

Another similar species is C. costellata ( Münster, 1832) ( Fig. 18 View Figure 18 ), but this species possesses riblets on the inner flanks. More differences can be seen in the ontogeny of the conch, C. formosa shows a clear triphasic ontogeny of the ww / dm ratio with a very slender juvenile stage (ww / dm = 0.30–0.35 at 6 mm dm). The inner whorls are stouter in C. costellata (ww / dm = 0.40–0.45 at 6 mm dm) ( Fig. 19 View Figure 19 ). Furthermore, C. costellata shows adult modifications such as a slightly tabulated venter and a deep terminal steinkern constriction.

C. formosa differs from C. subvexa from the Anti-Atlas in the nearly parallel flanks in the adult stage, which in C. subvexa converge more strongly towards the narrow venter. Furthermore C. subvexa has a more slender juvenile conch at 4 mm diameter (ww / dm ∼ 0.34 in C. formosa but ∼ 0.30 in C. subvexa ). The best criterion for the separation of the species is the form of the umbilical wall, which in C. formosa is steep, but oblique in C. subvexa (about 45 ◦). C. serotina differs from C. formosa in the almost smooth shell surface.

C. subcompressa Nikolaeva and Bogoslovsky, 2005 and C. pseudocompressa Nikolaeva and Bogoslovsky, 2005 have a similar shape, but the first species has an almost smooth shell and the second has lamellar growth lines, much coarser than in C. formosa View in CoL .