Alibashinautilus vetus Korn & Ghaderi, 2025, gen. et sp. nov.

Alibashinautilus vetus gen. et sp. nov. urn:lsid:zoobank.org:act: 4C7D84B1-4455-4069-A54B-3033FEB384A0 Figs 25–27; Table 15 Diagnosis Species of Alibashinautilus gen. nov. with thinly discoidal, evolute conch (ww/dm ~0.35; uw/dm ~0.50), equidimensional or weakly depressed whorl profile (ww/wh ~ 1.10–1.30) and moderately high coiling rate (WER ~1.85) at a conch diameter of 100–140 mm. Whorl profile nearly circular with continuously rounded venter and flanks; whorl overlap very small. Sculpture with short, coarse ribs on the outer flank. Suture line with wide and very shallow external lobe, very shallow lateral lobe and rather narrow, deep internal lobe. Etymology From the Latin ‘ vetus ’ (adj., m.) = ‘old’; since the species has a morphology similar to that of much older nautiloids. Type material Holotype IRAN – West Azerbaijan • Aras Valley; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Figs 25, 26A–B; MB.C.32053. Paratypes IRAN – East Azerbaijan • 1 specimen; Ali Bashi, main valley; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 26C–E; MB.C.32054 • 1 specimen; Ali Bashi; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); illustrated in Fig. 27; GLM # GH1006. Description Holotype MB.C.32053 is an incomplete internal mould with a diameter of almost 140 mm (Fig. 25). The study of conch shape and sculpture is only possible for about three quarters of the last volution, as the inner whorls are poorly preserved due to recrystallisation. The conch is thinly discoidal and evolute (ww/dm=0.30; uw/dm =0.50) and the whorl profile is nearly circular and slightly depressed (ww/ wh= 1.09). The overlap zone of the whorls is very small (Fig. 26A) and the coiling rate is moderately high (WER= 1.85). The sculpture consists of prominent ribs, which are coarsest in the ventrolateral region and gradually decrease in strength towards the umbilicus. On the body chamber, these ribs become weaker, and at the greatest diameter of the specimen, only shallow radial folds remain. Half a volution has thirteen ribs. The suture line shows shallow undulation with broadly rounded lobes and saddles and a rather narrow, rounded internal lobe (Fig. 26B). Paratype MB.C.32054 is a whorl segment of nearly half a volution and comprising of two chambers of the phragmocone and a long portion of the body chamber (Fig. 26C). Its conch diameter can be estimated with about 132 mm. The conch is serpenticonic with a wide umbilicus (uw/dm ~ 0.52) and a weakly depressed subcircular whorl profile (ww/wh=1.28). The coiling rate is moderate (WER ~1.91) and the whorl overlap zone very small (Fig. 26D). The sculpture is composed of low ribs confined to the flanks. They are coarsest in the ventrolateral area and become continuously weaker across the flanks before they disappear near the umbilicus. The siphuncle has a subcentral position on the dorsal side at about a quarter of the whorl heigh. Remarks Alibashinautilus vetus gen. et sp. nov. can be easily distinguished from A. ambiguus gen. et sp. nov. by the coarser ribs on the outer flank. Other differences are the greater width of the umbilicus (uw/dm ~ 0.50 in A. vetus, but only ~ 0.37 in A. ambiguus) and the lower coiling rate (WER ~ 1.85 in A. vetus in contrast to ~ 2.30 in A. ambiguus).