Lituites perfectus Wahlenberg 1818
Creators: name: Aubrechtová, Martina
name: Korn, Dieter
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Orthocerida
Lituitidae
Lituites
Lituites perfectus

description: Lituites perfectus Wahlenberg, 1818
Figs 37–42, Tables 9–11
Lituites perfectus Wahlenberg, 1818: 83.
Lituites perfectus – Remelé 1880: pl. 1 fig. 2; 1890: pl. 1 fig. 2, pl. 6 fig. 3. — Holm 1891: 12, pl. 2 figs 1–5. — Hardt 1953: 45, text-fig. 10.
Lituites lituus? – Aubrechtová & Meidla 2020: 286, text-fig. 14l.
? Lituites perfectus – Balashov 1953: pl. 14 fig. 4. — Sweet 1958: 144, pl. 16 fig. 4.
Diagnosis
Species of the genus Lituites with coiled part ca 29–40 mm in diameter; coiling open, eccentric, only innermost whorls contiguous, end part of the last whorl might be in the proximity or in contact with preceding whorl; whorl expansion rate ca 2.00. Backcoiled part of the conch weakly curved, expansion angle ca 1°, later up to 4°. Shell ornament with growth lines and annuli or ribs; rectiradiate in the coiled part and prorsiradiate in the backcoiled part. Ventral sinus deep with a ventral band, shallow lateral sinus just in front of the moderately high ventrolateral projection.
Type material
Neotype GERMANY • Mecklenburg-Vorpommern, Lansen (Malchin); Ordovician (late Lasnamägi or Uhaku regional stages, late Darriwilian), Upper Grey Orthoceratite Limestone; Krueger Coll.; MB.C.30544 (illustrated in Fig. 38A).
Additional material
GERMANY • 2 specs; Brandenburg, Eberswalde; Ordovician, Upper Grey Orthoceratite Limestone; Kgl. Forstakademie Eberswalde Coll.; MB.C.11622, MB.C.11646 • 1 spec.; Brandenburg, Niederfinow; Ordovician, Upper Grey Orthoceratite Limestone; Neben Coll.; MB.C.30542 • 1 spec.; Brandenburg, Oderberg (Bralitz); Ordovician, Upper Grey Orthoceratite Limestone; Krueger Coll.; MB.C.30543.
POLAND • 1 spec.; Kujawi-Pomerania, Bydgoszcz (former Bromberg); Ordovician, Upper Grey Orthoceratite Limestone; MB.C.30545.
Description
Neotype MB.C.30544 (Fig. 38A) consists of the coiled part (dm = 39 mm, 2.5 openly, eccentrically coiled volutions not touching each other, Fig. 39A–E) and a short part of the backcoiled part (length = 32 mm; wh = 11.4 mm; EA <1°). The shell ornament is best preserved at the transition of the coiled part to the backcoiled part of the conch. Here, it consists of narrow annuli (1.8–2.4 mm apart) and delicate growth lines (up to 0.2 mm apart). They extend with a broad and shallow lateral sinus across the flanks and then turn forward for a moderately high ventrolateral projection. On the venter they form a deep sinus. The close approximation of the growth lines leads to the formation of a ventral band (Fig. 42). The dorsal projection is very low. The ornament elements are concavo-convex and change from rectiradiate to prorsiradiate towards the backcoiled part of the conch. The phragmocone chambers are 0.60 of whorl height.
Specimen MB.C.30542 (Figs 38B, 39F–J) consists of a coiled and uncoiled part of the conch and has essentially the same dimensions as the neotype. The shell ornament, however, differs as it possesses much coarser growth lines that stand in distances of 0.3–0.6 mm at the beginning of the backcoiled part. In the coiled part, at 18 mm diameter, there are sharp annuli standing about 1.2 mm apart (mid-flank area); they weaken out in the outer flank area. Sharp growth lines (irregularly spaced 0.05–0.2 mm) occur between and on the crests of the annuli. In the backcoiled part, the shell wall is mostly not preserved; ornament is visible only as imprints of narrow annuli. The ornament elements extend straight across the flank with a very shallow sinus close to the ventrolateral projection. The CLR is ~ 0.57, with an increasing trend during ontogeny; however, a rapid decrease in the CLR followed by a rapid increase occurs at the end of the coiled part (Fig. 41A–B).
Specimen MB.C.11646 (Figs 37B, 38C) is a coiled part of a conch with 29 mm diameter; only a very short portion of the uncoiled part preserved. The volutions are slightly more regularly coiled compared to the other specimens (Fig. 39K–O). The CLR is ca 0.38 with a general decreasing ontogenetic trend up to the end of the coiled part, where the CLR starts to increase (Fig. 41E–F). In specimen MB.C.30543, the CLR also appears to be relatively higher, where the conch uncoiling starts (Fig. 41C–D).
Remarks
The name Lituites perfectus was introduced by Wahlenberg (1818); the original work was then republished later (Wahlenberg 1821); this caused some later authors to erroneously use the latter year of the species description. Wahlenberg (1818) did not describe or illustrate any type material and only referred to a specimen depicted previously by Walch (1771: pl. 4 fig. 1) as “the best example” of L. perfectus. Later, Holm (1891) reviewed the species and identified two probable originals of Wahlenberg (1818) in the collections of the Uppsala University, Sweden. However, Holm (1891) concluded that both specimens are too poorly preserved to be determined and might even represent two different species. He also pointed out that the specimen figured by Walch (1771) contradicts the brief description of Wahlenberg (1818) because its apical part is loosely, not tightly coiled. Despite that, Holm (1891) and other authors regarded the specimen of Walch (1771) as the type of Lituites perfectus.
The illustration of the specimen of Walch (1771: pl. 4 fig. 1) is a drawing, which shows a section through a lituiticonic conch with loosely coiled apical portion and a slightly curved, almost tubular uncoiled portion. Based on this illustration, it is not possible to determine the species identity of the specimen because the shell ornament is not shown and the above combination of characters is present in several lituitid species, such as Lituites nebeni sp. nov., Trilacinoceras discors or T. filix sp. nov.
The ambiguous interpretation of Lituites perfectus led to an inconsistent use of the name and specimens with variable conch shapes were thus assigned to the species. Lituites perfectus was most commonly confused with L. lituus. The herein studied material enabled the recovery and re-definition of L. perfectus and selection of a neotype. For further discussion, see remarks under L. lituus above.
Lituites perfectus differs from L. lituus in the larger diameter of the coiled conch, openly coiled volutions (tightly or almost tightly coiled in L. lituus), in the backcoiled part being weakly curved or straight (moderately to strongly curved in L. lituus), in the lower expansion angle of the conch (less than 1°–4° but 5°–8° in L. lituus) and in the generally finer ornament of the shell (L. lituus has annuli along the whole conch length).
The species most similar to L. perfectus is L. kruegeri sp. nov.; the coiled part of both species is relatively large (more than 30 mm in diameter), the volutions are openly coiled and the uncoiled part is almost straight with a low expansion angle (~ 1°). However, L. perfectus, has a less regular (eccentric) coiling geometry and a more prominent shell ornament compared to L. kruegeri sp. nov.
Lituites bottkei sp. nov. is openly coiled but its conch diameter is smaller (26 mm) compared to L. perfectus, the coiling is regular (not eccentric) and the uncoiled part is moderately curved with a greater expansion angle (6°–7° vs 1–3° in L. perfectus). In L. dewitzi sp. nov., only the last half whorl is detached from the preceding (inner volutions are tightly coiled), the coiled part diameter is smaller (27 mm) than in L. perfectus, the uncoiled part has an expansion angle of 5° and the general character of ornament is different (especially in the prorsiradiate direction of ornament elements in the coiled part of the conch).
The variation in L. perfectus concerns mainly the conch diameter and the degree of eccentricity of coiling (Figs 39–40).
The illustration of specimen MB.C. 11622 in Remelé (1890: pl. 1 fig. 2; reproduced here in Fig. 37A) is an idealised reconstruction of a rather poorly preserved, fragmentary specimen. Re-study of the specimen revealed, however, that the diagnostic characters of L. perfectus are present and the assignment to this species is plausible.
Geographic and stratigraphic occurrence
Norway (?), Sweden (?), Estonia (in situ) and northern Germany and northern Poland (in erratics within Pleistocene gravels); late Darriwilian, Middle Ordovician.
Lituites perfectus is a stratigraphically significant species in Baltoscandia indicating the late Lasnamägian age (e.g., Jaanusson 1960; Evans et al. 2014).
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 58-64, DOI: 10.5852/ejt.2022.799.1681, http://zenodo.org/record/6341270