Permonautilus adelphidus Korn & Hairapetian, 2025, sp. nov.

Permonautilus adelphidus sp. nov. urn:lsid:zoobank.org:act: C05CE182-FAC1-48A2-8930-80AC19A205B6 Figs 27–28; Table 21 Permonautilus sp. – Korn et al. 2021: text-fig. 17d. Diagnosis Species of Permonautilus with thinly globular, subinvolute conch (ww/dm = 0.90–1.00; uw/ dm =0.18–0.25), strongly depressed whorl profile (ww/wh =2.00–2.20) and extremely high coiling rate (WER =2.50–2.70) at a conch diameter of 20–60 mm. Whorl profile with broadly arched venter and flanks, broadly rounded umbilical margin, convex umbilical wall and moderately wide imprint zone (IZR ~ 0.20). Without sculpture. Suture line nearly straight. Etymology From the Greek ‘ἀδελφή’= ‘sister’ and ‘εἶδος’= ‘species’; because of its close relationship with P. abichi. Type material Holotype IRAN – Esfahan Province • Baghuk Mountain; Hambast Formation, Araxoceras beds (early Wuchiapingian); 2011; Korn et al. leg.; illustrated in Fig. 27; MB.C.30226. Paratypes IRAN – Esfahan Province • 1 specimen; same data as for holotype; 2011; Korn et al. leg.; illustrated in Fig. 28A–C; MB.C.32143 • 1 specimen; same data as for holotype; 2011; Ghaderi leg.; illustrated in Fig. 28D; MB.C.32144 • 1 specimen; same data as for holotype; 2011; Korn et al. leg.; illustrated in Fig. 28 E-F; MB.C.32145. Description Holotype MB.C.30226 is a strongly corroded, fully chambered specimen with a conch diameter of 48 mm (Fig. 27A). The conch is globular and subinvolute (ww/dm= 0.91; uw/dm = 0.25) with an extremely high coiling rate (WER = 2.62) and a moderately wide whorl overlap (IZR =0.16). The whorl profile is reniform and very strongly depressed (ww/wh = 2.02) with a broadly convex venter that merges continuously with the flanks. The umbilical margin is broadly rounded and the umbilical wall is steep and convex (Fig. 27B). The suture line describes an almost straight line (Fig. 27C). The last volution possesses 18 phragmocone chambers (CLI =20). Paratype MB.C.32143 is an incomplete, in part strongly corroded specimen with a conch diameter of 58 mm (Fig. 28B). About 135° of the final whorl belong to the body chamber. It has similar conch proportions to holotype MB.C.30226, but it is stouter; the conch is thickly globular and subinvolute (ww/dm= 1.02; uw/dm=0.21) with an extremely high coiling rate (WER =2.69) and a moderately wide whorl overlap (IZR =0.18). The whorl profile is very strongly depressed (ww/wh =2.15) with a broadly convex venter that merges continuously with the flanks. The umbilical margin is broadly rounded and the umbilical wall is steep and convex (Fig. 28A). The suture line extends almost linearly across flanks and venter (Fig. 28C). The last half volution possesses 8 phragmocone chambers (CLI =22.5). Paratype MB.C.32144 is a small, incomplete phragmocone specimen with a conch diameter of 38 mm (Fig. 28D). Part of the final whorl is missing; therefore, it allows an insight into the earlier ontogenetic conch growth. It shows that the basic conch proportions seem to change little during ontogeny; only the umbilicus becomes narrower. The conch is, at 38 mm diameter, globular and subinvolute (ww/dm = 0.95; uw/dm =0.22) with an extremely high coiling rate (WER =2.59) and a moderately wide whorl overlap (IZR =0.17). The whorl profile is very strongly depressed (ww/wh =2.08) with a broadly convex venter that merges continuously with the flanks. The geometry is almost identical at a conch diameter of 21 mm. Paratype MB.C.32145 is the largest individual with a conch diameter of 77 mm. It is a rather strongly weathered fragmentary specimen, but it allows the study of conch geometry at the transition to the adult stage, which is characterised by flattening of the venter (Fig. 28E). The conch is, with a ww/dm ratio of 0.83, slenderer than the other specimens. Its suture line extends almost linearly across flanks and venter (Fig. 28F). Remarks Permonautilus adelphidus sp. nov. is very similar to P. abichi, but differs in that it has a significantly higher whorl expansion rate at apparently all ontogenetic stages. In the growth interval between a conch diameter of 20 and 60 mm, the whorl expansion rate for P. adelphidus is always higher than 2.50, while for P. abichi it is only about 2.25–2.35. Another distinguishing feature is the shape of the shell: The ww/ dm ratio in P. adelphidus is higher than 0.90 in the interval between 20 and 60 mm shell diameter, while in P. abichi it is somewhat lower (0.80–0.90).