Lutonautilus cymus, Korn & Hairapetian, 2025

Lutonautilus cymus gen. et sp. nov.

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Fig. 22 View Fig ; Table 16 View Table 16

Diagnosis

Species of Lutonautilus gen. nov. with thinly discoidal, subinvolute conch (ww/dm ~ 0.35; uw/dm ~ 0.35), nearly quadrate whorl profile (ww/wh ~ 0.95) and high to very high coiling rate (WER ~2.30) at a conch diameter of 70–80 mm. Whorl profile with nearly parallel flanks; venter flatly rounded, flanks flattened, umbilical margin rounded, umbilical wall rounded. Sculpture with about 20 blunt lateral ribs per volution; they begin at the umbilical margin and are strengthened on the inner and outer flank to form elongate nodes. Suture line with a moderately deep external lobe and a moderately deep, broadly rounded lateral lobe.

Etymology

From the Greek ‘κῦμα’= ‘wave’; because of the undulated suture line.

Type material

Holotype

IRAN – Esfahan Province • Baghuk Mountain ; Hambast Formation, Vedioceras beds ( late Wuchiapingian); 2010; Korn et al. leg.; illustrated in Fig. 22 View Fig ; MB.C.32131 .

Paratypes

IRAN – Esfahan Province • 1 specimen; same data as for holotype; MB.C.32132 • 1 specimen; same data as for holotype; 2010; Ghaderi leg.; MB.C.32133.

Description

Holotype MB.C.32131 is an incomplete specimen with a conch diameter of 71 mm; it is almost completely chambered ( Fig. 22A View Fig ). The conch is thinly discoidal and subevolute (ww/dm = 0.35; uw/ dm =0.36) with a very high coiling rate (WER =2.29). The whorl profile is almost as wide as high (ww/ wh =0.97) and shows a flatly rounded venter and broadly rounded ventrolateral shoulders. The flanks are flattened and nearly parallel; the umbilical margin is continuously rounded ( Fig. 22B View Fig ). The sculpture consists of low, blunt ribs that start at the umbilical margin and extend with a shallow sinus across the flank. Most of these ribs are most coarsely developed on the inner and outer flank, where they form conical nodes, which are as wide as their interspaces. The suture line has a moderately deep, broadly rounded external lobe and a lateral lobe that is about twice as deep and broad ( Fig. 22C View Fig ). There are 10 septa on the last half whorl (CLI=18).

Remarks

Lutonautilus cymus gen. et sp. nov. differs from L. cratus gen. et sp. nov. and L. elachus gen. et sp. nov. in the shape of the ribs, which in L. cymus extend with a concave curve across the flanks, but in the other two species are almost straight. Furthermore, the ribs of L. cymus are weakly developed in the middle of the flank and strengthened and forming nodes on the outer and inner flanks, while those of L. cratus and L. elachus do not form nodes and are strongly developed in the middle of the flank.