Serometacoceras arasense, Korn & Ghaderi, 2025

Serometacoceras arasense gen. et sp. nov.

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Fig. 24 View Fig ; Table 14 View Table 14

Pleuronautilus sp. – Gliwa et al. 2020: text-fig. 17d.

Diagnosis

Species of Serometacoceras gen. nov. with thinly discoidal, subinvolute conch (ww/dm ~0.45; uw/dm ~0.28), nearly quadrate whorl profile (ww/wh ~0.90) and extremely high coiling rate (WER ~2.70) at a conch diameter of 80 mm. Whorl profile flattened, parallel flanks; venter broadly rounded, flanks slightly flattened, umbilical margin subangular. Sculpture with about 15 short lateral plications per volution.

Etymology

Named after the type locality at the Aras River ( West Azerbaijan, Iran).

Type material

Holotype

IRAN – West Azerbaijan • Aras Valley ; Zal Member of the Ali Bashi Formation ( 9.50 m below top) ( early Changhsingian); 2011; Korn et al. leg.; illustrated in Fig. 24 View Fig ; MB.C.29349 .

Description

Holotype MB.C.29349 is rather complete and has a conch diameter of 82 mm ( Fig. 24B View Fig ). It is preserved with adherent shell material but does not show the suture line. The conch is thinly discoidal and subinvolute (ww/dm ~ 0.43; uw/dm =0.28); the whorl profile is slightly compressed and subquadrate (ww/wh = 0.92) with flattened, parallel flanks, a pronounced ventrolateral shoulder and a broadly rounded venter ( Fig. 24A View Fig ). The umbilical margin is subangular in the last half of a volution with an obliquely oriented umbilical wall. In contrast, the penultimate volution (up to about 30 mm dm) has a very pronounced umbilical margin and an almost vertical umbilical wall.

The sculpture of the last volution is dominated by weakly protracted radial plications. They begin at the umbilical margin, where they bear small tubercles, and gain in strength across the flanks. They terminate at the ventrolateral shoulder where they are coarsest and bear another row of tubercles. The umbilical opening allows the study of the sculpture in the preceding whorl, in which the ribs are much coarser than in the last and the umbilical margin is more pronounced and bears a ridge occupied with small tubercles.

Remarks

Serometacoceras arasense gen. et sp. nov. differs from S. costale (Shimansky, 1965) gen. et comb. nov. in the shape of the whorl profile; in S. arasense the ww/wh ratio is about 0.90 and in S. costale only 0.60– 0.70 ( Shimansky 1965b). In addition, S. arasense has significantly coarser radial ribs than S. costale .

Serometacoceras arasense gen. et sp. nov. differs from the other species of the genus Serometacoceras gen. nov. of Julfa by the prominent umbilical margin in the adult stage.