Trocholites triangulus, Aubrechtová & Korn, 2025

Trocholites triangulus sp. nov.

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Fig. 23 View Fig ; Table 14 View Table 14

Diagnosis

Species of the genus Trocholites with an adult conch diameter of 26 mm. Conch in the last whorl thinly discoidal (CWI ~ 0.33) and evolute (UWI ~ 0.55). Whorl profile depressed (WWI ~ 1.50) with rounded flanks, venter narrowed down, whorl widest dorso-laterally. Whorl width and whorl height increasing in last quarter volution. Phragmocone chambers moderately long (RCL ~ 0.38). Suture line straight.

Etymology

From the Latin ‘ triangulus ʼ (nomen) = ‘a triangle’, referring to the shape of the apertural whorl profile of the holotype given by the narrowed venter.

Material examined

Holotype

GERMANY – Mecklenburg-Vorpommern • Göhren (Isle of Rügen); Lasnamägi Regional Stage ; 1968; Krueger Coll.; illustrated in Fig. 23 View Fig ; MB.C. 32176.

Description

Specimen MB.C.32176 ( Fig. 23 View Fig ) is a small adult conch with only 25 mm diameter; it is extremely discoidal (CWI = 0.33) and evolute (UWI = 0.57) with a depressed last whorl (WWI = 1.50). The venter of the outer whorl is not rounded but is narrowed down and the whorl appears to be widest dorso-laterally. The relative chamber length (RCL) is 0.38. The body chamber has a length of slightly more than half a volution and its aperture possesses lateral and ventrolateral flares (the ventral part cannot be seen).

Remarks

The holotype of Trocholites triangulus sp. nov. is similar to specimens MB.C.32161 and MB.C.32160, which belong to T. depressus , and specimen MB.C.32182 (T. sp. 4) ( Fig. 7 View Fig ). However, the former differs by the ventrally narrowed external volution. The arched, keel-like shape of the outer ventral side of the conch is known in specimens of Trocholites gracilis from the late Chazyan Valcour Limestone of New York ( Flower 1943); the adult conch size (dm 24 mm) is similar to Trocholites triangulus and suture line in both species is essentially straight. The last half a whorl in the latter is, however, depressed, instead of slightly compressed (WWI = 1.50 vs 0.93).