Serometacoceras pentagonum, Korn & Hairapetian, 2025

Serometacoceras pentagonum sp. nov.

urn:lsid:zoobank.org:act:

Fig. 15 View Fig ; Table 9 View Table 9

Diagnosis

Species of Serometacoceras with thickly discoidal, subevolute conch (ww/dm ~ 0.50; uw/dm ~ 0.32), weakly depressed whorl profile (ww/wh ~1.15) and extremely high coiling rate (WER ~2.65) at a conch diameter of 40 mm. Whorl profile weakly depressed with nearly parallel flanks; venter broadly convex, flanks weakly concave. Sculpture with pairs of about 20 low ventrolateral nodes and weak umbilical nodes per volution; the nodes are connected by weak ribs on the midflank. Suture line with a shallow external lobe and a broadly rounded lateral lobe.

Etymology

From the Greek ‘πέντε’=‘five’ and ‘γόνυ’=‘knee, angle’; because of the pentagonal whorl profile.

Type material

Holotype

IRAN – Esfahan Province • Baghuk Mountain ; Hambast Formation, Araxoceras beds ( early Wuchiapingian); 2011; Ghaderi leg.; illustrated in Fig. 15 View Fig ; MB.C.32122 .

Description

Holotype MB.C.32122 is a rather small phragmocone with a conch diameter of only 38 mm ( Fig. 15B View Fig ). The conch is thickly discoidal and subevolute (ww/dm = 0.49; uw/dm = 0.32) with an extremely high coiling rate (WER= 2.65). The whorl profile is weakly depressed (ww/wh= 1.16) with a slightly convex venter and a broadly rounded ventrolateral shoulder. The flanks are very slightly flattened and slowly divergent; the umbilical margin is narrowly rounded and the umbilical wall is steep and convex ( Fig. 15A View Fig ). The sculpture consists of very low, about ten conical ventrolateral nodes on a half volution, which show a very weak continuation across the flanks and are connected to barely visible umbilical nodes. The suture line has shallow, broadly rounded external and lateral lobes and a very small lobe on the umbilical wall ( Fig. 15C View Fig ).

Remarks

Serometacoceras pentagonum sp. nov. is similar to the Transcaucasian species S. verae in conch shape. However, the two species differ in the suture line (external saddle in S. verae , external lobe in S. pentagonum ) and the sculpture (midflank nodes in S. verae ). Serometacoceras pentagonum differs from the other Transcaucasian species in the more robust conch (ww/dm ~ 0.50 in contrast to 0.40–0.45), the narrower umbilicus (uw/dm ~ 0.30 in contrast to ~0.35) and the convexly rounded venter.