Baghuknautilus aplomorphus Korn & Hairapetian, 2025, gen. et sp. nov.

Baghuknautilus aplomorphus gen. et sp. nov. urn:lsid:zoobank.org:act: 0E6D1116-BB35-4615-832A-A52849FB4934 Fig. 29; Table 22 Diagnosis Species of Baghuknautilus gen. nov. with thinly discoidal, involute conch (ww/dm ~0.40; uw/dm ~0.10), weakly compressed whorl profile (ww/wh ~ 0.65) and extremely high coiling rate (WER ~2.55) at a conch diameter of 60 mm. Whorl profile with convex venter, convex and convergent flanks, narrowly rounded umbilical margin, a steep umbilical wall and moderately wide imprint zone (IZR ~ 0.30). Suture line with a very shallow external lobe and an asymmetric, broadly rounded lateral lobe. Etymology From the Greek ‘ἁπλόος’=‘simple’ and ‘μορφή’= ‘form’; because of the rather simple conch morphology. Type material Holotype IRAN – Esfahan Province • Baghuk Mountain; Hambast Formation, Vedioceras beds (late Wuchiapingian); 2011; Korn et al. leg.; illustrated in Fig. 29A–C; MB.C.32146. Paratype IRAN – Esfahan Province • 1 specimen; Baghuk Mountain; Hambast Formation, Vedioceras beds (late Wuchiapingian); 2011; Korn et al. leg.; illustrated in Fig. 29D–E; MB.C.32147. Description Holotype MB.C.32146 is an incomplete, but on the left side rather well-preserved fully chambered specimen with a conch diameter of 83 mm (Fig. 29A). Some conch parameters can only be reconstructed. The conch is thinly discoidal and involute (ww/dm ~0.40; uw/dm=0.10). The whorl profile is weakly compressed (ww/wh ~0.64) with a convex venter and convex, convergent flanks. The umbilical margin is narrowly rounded and the umbilical wall is steep and convex (Fig. 29B). The last volution possesses about 22 phragmocone chambers (CLI=16.5) with an indication of crowding at the end. The siphuncle has a dorsocentral position. The suture line shows a small and very shallow lobe on venter, a broadly rounded asymmetric lateral lobe with steeper dorsal flanks and a shallow umbilical lobe (Fig. 29C). Paratype MB.C.32147 is a bilaterally corroded, fully chambered specimen with a conch diameter of 60 mm (Fig. 29E). Some conch parameters on the last half volution can only be reconstructed. The conch is thinly discoidal and involute (ww/dm=0.42; uw/dm =0.12) with an extremely high coiling rate (WER=2.54) and a deep whorl overlap (IZR = 0.32). The whorl profile is moderately compressed (ww/wh =0.76) with a convex venter and convex convergent flanks (Fig. 29D). The suture line shows a shallow, rounded lobe on venter and a broadly rounded slightly asymmetric lateral lobe with steeper dorsal flanks. Remarks Baghuknautilus aplomorphus gen. et sp. nov. differs from Shahrezanautilus ghaderii gen. et sp. nov. by the considerably slenderer conch; the ww/dm ratio is about 0.40 in B. aplomorphus but about 0.60 in S. ghaderii. The coiling rate is much lower in B. aplomorphus (WER higher about 2.50 in comparison with more than 3.00 in S. ghaderii).