Araeonema cf. tenuistriata ( Netchaev, 1894 )

Ketwetsuriya, Chatchalerm, Karapunar, Baran, Charoentitirat, Thasinee & Nützel, Al- Exander, 2020, Middle Permian (Roadian) gastropods from the Khao Khad Formation, Central Thailand: Implications for palaeogeography of the Indochina Terrane, Zootaxa 4766 (1), pp. 1-47 : 26

Araeonema cf. tenuistriata ( Netchaev, 1894)

( Fig. 18K )

cf. Turbo tenuistriata Netchaev, 1894 ; 349, pl. 11, fig 17.

cf. Araeonema tenuistriata ( Netchaev, 1894) ; Mazaev 2015: 954, pl. 31, figs 1–8.

Material. One specimen: ESKU-19- LP 99.

Dimensions (mm): ESKU-19- LP 99: height = 4.2; width = 2.9; apical angle = 80º.

Description. Shell small, turbiniform; blunt apex; whorls weakly convex, evenly rounded; whorls ornamented by 4 strong spiral cords, and fifth emerging at abapical suture; spiral cords equally spaced with concave interspaces; base convex with rounded transition to whorl face, bordered by a strong spiral cord; base ornamented with 12 narrowly spaced spiral cords; sutures deep, distinct; aperture seemingly circular.

Remarks. The single specimen at hand closely resembles Araeonema tenuistriata ( Netchaev, 1894) as reported by Mazaev (2015, p. 954, pl. 31, figs 1–8) from the Middle Permian of the Volga-Ural Region, Russia in shell shape, size and principal ornamentation. However, A. tenuistriata has a broader shell, more and weaker spiral cords and more convex whorls. A. tenuistriata is narrowly phaneromphalous but the umbilical area is not visible in the specimen at hand. A. tenuistriata is similar to A. panthalassica Nützel in Nützel & Nakazawa, 2012 from the Upper Middle Permian Akasaka Limestone, Japan but A. panthalassica is smaller, weaker spiral cords and a flatter apex. A. virgatum Knight, 1933 a (p. 52, pl. 9, fig. 3) from the Pennsylvanian of the Labette Shale, Missouri, USA has more and much finer spiral cords and its whorl are less convex. Both, A. novamexicanum Kues, 2004 from the Laborcita Formation, New Mexico and A. microspirulata Yoo, 1994 from the Early Carboniferous of Australia are similar to the present specimen but those species are broader and have very fine and many more spiral cords. A. problematicum Wang in Wang & Xi, 1980 from the Permian of China is similar in shell shape but the ornamentation cannot be compared meaningfully because of its poor preservation. A. cf. tenuistriata resemble Amaurotoma ? sp. as illustrated by Ketwetsuriya et al. (2016, p. 494, fig. 12A–C) from the Middle Permian Tak Fa Limestone, Thailand in having strong spiral cords, but differs in having a higher spire, steeper ramp and an angulated whorl profile. This is the first species which is referred to the genus Araeonema from Thailand and Southeast Asia.

Figures

FIGURE 18. A–J, Yunnania inflata sp. nov. A–B, ESKU-19-LP 9, holotype; C–G, ESKU-19-LP 65, paratype. H–J, juvenile specimens, H–I, ESKU-19-LP 205. J, ESKU-19-LP 215. K, Araeonema cf. tenuistriata (Netchaev, 1894), ESKU-19-LP 99. All scale bars represent 1 mm.