Ancistroceras torelli
Creators: name: Aubrechtová, Martina
name: Korn, Dieter
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Orthocerida
Lituitidae
Ancistroceras
Ancistroceras torelli

description: 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.
description: Published as part of Aubrechtová, Martina & Korn, Dieter, 2022, Taxonomy and ontogeny of the Lituitida (Cephalopoda) from Orthoceratite Limestone erratics (Middle Ordovician), pp. 1-108 in European Journal of Taxonomy 799 (1) on pages 36-40, DOI: 10.5852/ejt.2022.799.1681, http://zenodo.org/record/6341270