Ocunautilus diplodocus Korn & Hairapetian, 2025, gen. et sp. nov.

Ocunautilus diplodocus gen. et sp. nov. urn:lsid:zoobank.org:act: 46279074-DA8A-42D6-B45C-8C639250C01A Fig. 8; Table 4 Diagnosis Species of Ocunautilus gen. nov. with thinly discoidal, subinvolute conch (ww/dm ~0.42; uw/dm ~0.20), weakly compressed whorl profile (ww/wh ~ 0.85) and extremely high coiling rate (WER ~2.95) at a conch diameter of 100 mm. Whorl profile inverted trapezoidal with deeply concave venter, angular ventrolateral shoulder, flattened and weakly convergent flanks, angular umbilical margin and steep and weakly concave umbilical wall. Whorl overlap small (IZR ~ 0.12). Without sculpture. Suture line with a very deep, rounded V-shaped external lobe, an angular ventrolateral saddle, a shallow and broadly rounded lateral lobe and a very small umbilical lobe. Etymology From the Greek ‘διπλόος’=‘double’ and ‘ὀξύς’=‘sharp’; because of the double-keeled venter. Type material Holotype IRAN – Esfahan Province • Baghuk Mountain; Hambast Formation, Araxoceras beds (early Wuchiapingian); 2013; Korn et al. leg.; illustrated in Fig. 8; MB.C.32110. Paratypes IRAN – Esfahan Province • 2 specimens; same data as for holotype; 2010; Korn et al. leg.; MB.C.32111, MB.C.32112. Description Holotype MB.C.32110 is a fragment showing slightly more than a quarter whorl of the phragmocone and a poorly preserved piece of the penultimate whorl (Fig. 8A). The fragment has a maximum whorl height of 51 mm; from this, a diameter of 105 mm can be reconstructed. On the basis of this calculated diameter, the conch parameters can be determined. The conch is thinly discoidal and subinvolute (ww/ dm ~ 0.42; uw/dm ~ 0.21) with an extremely high coiling rate (WER ~ 2.96). The whorl profile is weakly compressed (ww/wh= 0.87) with a deeply concave venter that is bordered by a sharp, skid-like ventrolateral shoulder; the flanks are flattened and convergent. Most conspicuous is the angular umbilical margin, which borders the weakly concave, incurved umbilical wall (Fig. 8B). The whorl overlap is small (IZR =0.14). The specimen does not show any sculpture. The suture line is strongly influenced by the outline of the whorl profile; it is characteristic because of the narrow and deep, V-shaped external lobe, which is separated from the broadly rounded lateral lobe by a subangular ventrolateral saddle (Fig. 8C). The last quarter volution of the phragmocone consists of seven chambers (CLI = 13); there occurs weak septal approximation toward the aperture. Remarks Ocunautilus diplodocus gen. et sp. nov. differs from the other two species O. coelodesmus gen. et sp. nov. and O. tachytrephus gen. et sp. nov. from Baghuk Mountain by the much more deeply concave venter; accordingly, the external lobe of O. diplodocus is also much deeper and narrower.