Tainionautilus deinceps Korn & Ghaderi, 2025, sp. nov.

Tainionautilus deinceps sp. nov. urn:lsid:zoobank.org:act: C3803C00-1BBD-42EF-B58A-FDD573CCE5C5 Fig. 38; Table 23 Tainionautilus sp. – Shimansky 1965b: 158, pl. 15 fig. 8. ? Tainionautilus sp. indet. – Teichert & Kummel 1973: 419, pl. 3 figs 9–10. Diagnosis Species of Tainionautilus with thinly pachyconic, subinvolute conch and nearly quadrate whorl profile at a conch diameter of about 50 mm. Whorl profile with nearly parallel flanks; venter flattened with a very shallow longitudinal midventral groove, flanks slightly convex and weakly convergent, umbilical margin and ventrolateral shoulder broadly rounded. Sculpture with five rounded ribs per quarter volution, extending in forward direction from the umbilical margin and turn back on the flank. Occasionally, ribs are intercalated on the midflank. Venter almost smooth. Etymology From the Latin ‘ deinceps ’ (adj.) =‘forward’; because of the course of the ribs on the inner flank. Type material Holotype IRAN – East Azerbaijan • Ali Bashi N; Paratirolites Limestone (3.15 m below top) of the Ali Bashi Formation (late Changhsingian); 2012; Korn et al. leg.; illustrated in Fig. 38; MB.C.32064. Description Holotype MB.C.32064 is a segment of slightly over a quarter whorl, with a whorl height of 21 mm (Fig. 38A). Its whorl profile is weakly depressed and almost quadrate. The flanks are nearly parallel, while the umbilical margin and ventrolateral shoulder are rounded. The venter is flattened and has a shallow median groove (Fig. 38B). The sculpture is composed of low, fold-like ribs that are coarsest on the inner half of the flank. The ribs originate from the outer area of the umbilical wall and extend forward. As they reach the middle of the flank, they bend backwards and gradually weaken. They are hardly visible on the venter. Secondary ribs may occasionally appear between the primary ribs on the middle of the flank. Remarks Shimansky (1965b: 158) illustrated a specimen that likely belongs to this species, but kept it in open nomenclature. He listed four specimens, which came from the Paratirolites Limestone. It is less clear whether the specimen of “ Tainionautilus sp. indet.” (MCZ 9760) described by Teichert & Kummel (1973: 419) also belongs to T. deinceps sp. nov. With a whorl height of 30 mm, it has a more depressed whorl profile (ww/wh ~1.35) than the holotype of T. deinceps (ww/wh ~ 1.25). However, this difference could be due to ontogenetic changes; the holotype has a whorl height of only 21 mm. The specimen illustrated by Shimansky (1965b: pl. 15 fig. 8) lies in between (ww/wh ~1.30) with a whorl height of 25 mm. Tainionautilus deinceps sp. nov. can be easily distinguished from the other species of the genus by the very prominent, anteriorly directed ribs on the inner half of the flank. In T. deinceps the ribs are weakly developed in the ventrolateral region, whereas in the other species they are most strongly developed there.