Ancistroceras Boll, 1857

Aubrechtová, Martina & Korn, Dieter, 2022, Taxonomy and ontogeny of the Lituitida (Cephalopoda) from Orthoceratite Limestone erratics (Middle Ordovician), European Journal of Taxonomy 799 (1), pp. 1-108 : 28-29

Genus Ancistroceras Boll, 1857

Type species

Lituites undulatus Boll, 1857 ; by monotypy.

Diagnosis

Genus of the family Lituitidae with 1.5–2 tightly coiled or only slightly separated early volutions; long, rapidly expanding straight part; umbilical window small. Whorl profile elliptic or circular in the coiled stage, circular in the uncoiled stage. Uncoiled part expands with an angle of 18–35° and is straight in longitudinal profile. Shell surface with sinuous growth bands and annulations, which form five projections in the coiled part, three and finally two in the straight part. Aperture of mature conch with broad dorsal and ventral projections and shallow lateral sinus (after Aubrechtová & Meidla 2020).

Species included

Ancistroceras Barrandei Dewitz, 1880 ; Ancistroceras Bollii Remelé, 1882 ; Ancistroceras clinotum Xu & Lai, 1987 ; Ancistroceras densum Qi, 1980 ; Sinoceras fengxiangense Chang, 1964 ; Ancistroceras magnum Flower, 1975; Ancistroceras ristnensis Aubrechtová & Meidla, 2020 ; Ancistroceras subcurvatum Qi, 1980 ; Strombolituites Torelli Remelé, 1881; Lituites undulatus Boll, 1857 ; Ancistroceras vahikuelaensis Aubrechtová & Meidla, 2020 .

Remarks

The authorship of Ancistroceras is a confusing matter. Boll (1857: 87) stated in the description of his new species Lituites undulatus that he originally planned to define a new genus Ancistroceras for this species, but then changed his mind. However, Boll (1857: 3, fig. 25) presented the species as Ancistroceras undulatum . Dewitz (1880: 387) restored the genus name and designated L. undulatus as the type species. Boll (1857) was then accepted throughout the literature as the author of the genus Ancistroceras . This view is also followed here.

In contrast to Rhynchorthoceras , species of the genus Ancistroceras are characterised by a coiled early juvenile conch, a greater expansion angle, a larger chamber length ratio and a strongly annulated shell surface. Representatives of the genus Holmiceras are similar to species of Ancistroceras , but the former are distinguished by an openly coiled juvenile conch part and a sigmoidally shaped backcoiled part with a smaller expansion angle.

Geographic and stratigraphic occurrence

North America, Wales (?), Baltoscandia, northern Germany, the Kaliningrad Region of Russia, northern Poland and China; Middle to Late Ordovician. The stratigraphically oldest species of Ancistroceras were described from early Dapingian strata of China and hence belong to the earliest lituitids known to date ( Kröger et al. 2007; Fang et al. 2021).