Kazakhstania evoluta

Kazakhstania evoluta (Vöhringer, 1960)

Figs 10E, 87–88; Tables 83–84

Gattendorfia evoluta Vöhringer, 1960: 159, pl. 5 fig. 4.

Gattendorfia evoluta – Korn 1994: 74, text-figs 65i, 66l, 67h, 68f. — Sprey 2002, pl. 4 fig. 3.

non Gattendorfia evoluta – Bockwinkel & Ebbighausen 2006: 112, text-figs 29, 30e –h.

Species of Kazakhstania with a conch reaching 30 mm diameter. Conch at 15 mm dm thinly discoidal, very evolute (ww/dm ~0.40; uw/dm ~0.65). Whorl profile at 15 mm dm moderately depressed (ww/wh ~1.80); coiling rate very low (WER ~1.48). Venter weakly flattened. Growth lines very fine, narrow-standing, with convex course. Without constrictions on the shell surface. Suture line with very narrowly lanceolate external lobe.

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, loose material; Vöhringer Coll.; illustrated by Vöhringer (1960: pl. 5 fig. 4), Korn (1994: text-fig. 65i) and Sprey (2002: pl. 4 fig. 3); re-illustrated here in Fig. 87; GPIT-PV-63963.

Paratype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2; Vöhringer Coll.; GPIT-PV-63965.

Additional material

GERMANY • 2 specimens; Rhenish Mountains, Oese, old quarry; Hangenberg Limestone, bed 30; Weyer & Korn 2000 Coll.; MB.C.5258.1, MB.C.5258.6.

Holotype GPIT-PV-63963 is a moderately well-preserved specimen with 23 mm conch diameter (Fig. 87). It displays the characteristic conch geometry with a very wide umbilicus (uw/dm = 0.63) and a depressed rectangular whorl profile (ww/wh = 1.88) with a flattened venter and uniformly convex flanks. Shell remains are present in some places; they show very fine growth lines, standing approximately 0.2 mm apart. They are clearly directed backwards from the umbilicus and form a broad ventral sinus (Fig. 88C). The suture line has a very narrow, lanceolate external lobe (Fig. 88B).

The sectioned paratype GPIT-PV-63965 shows only minor ontogenetic changes in conch geometry up to a conch diameter of 14 mm (Fig. 88A). The whorl profile of all whorls larger than 4 mm conch diameter is rounded trapezoidal with a flattened venter. The ontogenetic trajectories are monophasic (Fig. 88D– F); the umbilical width increases slightly in early ontogeny and remains at a very high value above 0.60 from a conch diameter of 5 mm.

Kazakhstania evoluta can be distinguished from almost all other species of the genus by the absence of constrictions. Similar in this respect is only E. kana sp. nov. from the Anti-Atlas of Morocco; this species, however, has a pouched external lobe that is about twice as wide and is thus clearly different from K. evoluta.