Tainoceras unitum Korn & Ghaderi, 2025, sp. nov.

Tainoceras unitum sp. nov. urn:lsid:zoobank.org:act: 1F60FF8F-3ABB-4B98-ABED-853626335165 Fig. 36 Diagnosis Species of Tainoceras with thinly pachyconic, subevolute conch and nearly quadrate whorl profile (ww/wh ~ 1.10) at a conch diameter of about 80 mm. Whorl profile with weakly convergent flanks; venter flattened with a broad longitudinal midventral groove, flanks sinuous, umbilical margin narrowly rounded. Sculpture with five coarse ribs per quarter volution, extending from the umbilical margin to the midventral groove, strengthened to form small, longitudinally elongated nodes on the ventrolateral shoulder and the venter. Suture line with a very shallow external lobe and a broadly rounded, very shallow lateral lobe. Etymology From the Latin ‘ unitum ’ (verb in participle) =‘united’; because of the amalgamated ventrolateral and ventral nodes. Type material Holotype IRAN – West Azerbaijan • Zal; Zal Member of the Ali Bashi Formation (early Changhsingian); 2018; Ghaderi leg.; illustrated in Fig. 36; MB.C.32062. Description The fragmentary holotype MB.C.32062 has a whorl height of 30 mm and thus may belong to a specimen with a conch diameter of about 80 mm (Fig. 36A). Its whorl profile is almost quadrate but slightly depressed (ww/wh = 1.06) with narrowly rounded umbilical margin, flattened slowly converging flanks, rounded ventrolateral shoulders and a flattened venter with a shallow and broad longitudinal groove (Fig. 36B). The sculpture of the fragment shows five rounded ribs on the whorl segment of 90 degrees. These ribs are slightly concave in their course; they begin on the inner flanks and become more prominent to terminate in pronounced ventrolateral nodes, which have a position on the outer flank. On the venter, another row of nodes is present adjacent to the ventral groove. The ventrolateral and ventral nodes are corresponding and connected by a blunt rib. The suture line is weakly undulate with very shallow, broadly rounded external and lateral lobes (Fig. 36C). Remarks Tainoceras unitum sp. nov. has a similar conch shape and sculpture to that of T. latecostatum sp. nov., but differs in the blunt flank ribs (which are sharp in T. latecostatum) and the much thicker ventral nodes, which are very weakly developed in T. latecostatum. Another difference between the two species is the rib-like connection of the ventrolateral and ventral nodes in T. unitum, whereas these are separate in T. latecostatum. Tainoceras unitum sp. nov. differs from many other species of the genus in the presence of flank ribs. In addition, the almost complete fusion of the ventrolateral and ventral nodes is not developed in the other species.