Ancistroceras torelli ( Remelé, 1881 )

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 : 36-40

Ancistroceras torelli ( Remelé, 1881)

Figs 23D–E , 24–25 , Tables 4–5

Strombolituites Torelli Remelé, 1881: 192, text-fig. 2.

Ancistroceras Torelli – Noetling 1884: pl. 18 fig. 7. — Holm 1885: pl. 4 fig. 2. — Remelé 1890: pl. 4 fig. 1.

Ancistroceras torelli – Balashov 1962: pl. 9 fig. 8. — Neben & Krueger 1971: pl. 17 figs 2, 7.

? Ancistroceras torelli – Foerste 1930: pl. 41 fig. 2a–b. — Dzik 1984: pl. 39 figs 8–9, pl. 40 figs 1–2.

Diagnosis

Species of the genus Ancistroceras with strongly curved end of the coiled part of the conch; uncoiled part of the conch straight; expansion angle ca 30°. Whorl profile slightly depressed in the coiled part and circular in the uncoiled part of the conch. Ornament with distinct, narrow annuli and lirae, welldeveloped even in the coiled part of the conch. Ornament with shallow lateral sinus, low dorsal projection and ventral sinus; the latter deep at the coiled part and flattened out in the uncoiled part of the conch.

Type material

Lectotype (designated here) GERMANY • Brandenburg, Heegermühle; erratics in Pleistocene gravel, Ordovician, Upper Grey Orthoceratite Limestone; illustrated by Remelé (1881: text-fig. 2; 1890: pl. 4 fig. 1) and Neben & Krueger (1971: pl. 17 fig. 7); re-illustrated here in Fig. 23D , 24 , 25A ; MB.C.22575 .

Paralectotype GERMANY • Brandenburg, Schmetzdorf; Ordovician, Upper Grey Orthoceratite Limestone; Neben and Krueger Coll.; MB.C.30519 .

Description

Lectotype MB.C.22575 ( Figs 23D , 24 , 25A ) is undeformed but some measurements are difficult to obtain because of an imprecise, oblique section that was ground by a previous researcher. The conch consists of the coiled part (dm = 20.5 mm; tightly coiled; WER>3) and the straight uncoiled part (length = 33 mm long; wh ~ 32 mm; EA ~ 32°). The shell ornament consists of raised lines in the coiled part of the conch, but towards the uncoiled part of the conch, these lines grade into narrow but clearly marked annuli (2.5 mm apart) with lirae 0.5 mm apart. The chamber length can be measured precisely only at the end of the uncoiled part of the specimen (CLR = 0.18 at wh = 28 mm). The siphuncle has a central position and measures ca 0.12 of the whorl height.

Paralectotype MB.C.30519 ( Figs 23E , 25B ) is similar in size to the lectotype. The conch consists of the coiled part (dm = 19.7 mm; tightly coiled; WER ~ 5) and the straight uncoiled part (length = 41 mm; wh = 31 mm; EA ~ 29°). The shell ornament consists of narrow annuli that are clearly visible along the whole extension of the conch including the coiled part. Their distances increase gradually from 0.7 mm to 2.5 mm. The annuli are accompanied by lirae (0.5 mm apart). The ornament elements form a low dorsal projection, a shallow lateral sinus and a ventral sinus, which is deep in the coiled part and flattens out in the uncoiled part.

Remarks

Unlike the other species of the genus, Ancistroceras torelli has distinctly developed annuli even in the coiled part of the conch. Additionally, the species differs from the above described A. undulatum in the stronger curvature at the end of the coiled part and from A. barrandei in a much larger expansion angle (ca 30°). Ancistroceras bollii ( Remelé, 1882) from the Darriwilian erratics of northern Germany has a more bulbous conch than A. torelli and it is generally smaller, ventrally curved and retains the circular whorl profile during ontogeny.

Geographic and stratigraphic occurrence

Northern Germany and northern Poland (in erratics within Pleistocene gravels); late Darriwilian, Middle Ordovician.

According to Remelé (1881), the lectotype originated from the “light grey orthoceratite limestone”, where it co-occurs with Lituites perfectus and the trilobites Asaphus sp., Illaneus sp. and Hoplolichas tricuspidatus Beyrich, 1846. This co-occurrence suggests a late Darriwilian (probably Lasnamägian) age of the lectotype.

Figures

Fig. 23. Comparison of the coiled parts of species of Ancistroceras Boll, 1857 from the Upper Grey Orthoceratite Limestone. A. Ancistroceras barrandei Dewitz, 1880, specimen MB.C.30518 (Neben & Krueger Coll.) from Rerik (Ostsee). B. Ancistroceras barrandei Dewitz, 1880, specimen MB.C.30516 (Neben & Krueger Coll.) from Rerik (Ostsee). C. Ancistroceras barrandei Dewitz, 1880, specimen MB.C.11991 (Helms 1966 Coll.) from Gross Zicker (Island of Rügen). D. Ancistroceras torelli (Remelé, 1881), lectotype MB.C.22575 from Heegermühle (Brandenburg). E. Ancistroceras torelli (Remelé, 1881), specimen MB.C.30519 (Neben & Krueger Coll.) from Schmetzdorf (Brandenburg). Scale bar units = 1 mm.

Fig. 24. Ancistrocerastorelli(Remelé, 1881)from the Upper Grey OrthoceratiteLimestone.Reproduction of the illustration of lectotype MB.C.22575 from Heegermühle (Brandenburg) from Remelé (1890: pl. 4 fig. 1). Scale bar units = 1 mm.

Fig. 25. Ancistroceras torelli(Remelé, 1881) from the Upper Grey Orthoceratite Limestone. A. Lectotype MB.C.22575 from Heegermühle (Brandenburg); dorso-lateral view. B. Specimen MB.C.30519 (Neben & Krueger Coll.) from Schmetzdorf (Brandenburg); dorsal, lateral and ventral views. Scale bar units = 1 mm.