Lituites toernquisti Holm, 1891

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 : 64-66

Lituites toernquisti Holm, 1891

Figs 43–44 , Tables 9–10

Lituites Törnquisti Holm, 1891: 9 , pl. 1 figs 1–4.

Lituites törnquisti – Sweet 1958: 124, 147.

? Lituites lituus – Hucke 1967: 56, pl. 17 fig. 5.

Lituites sp. – Neben & Krueger 1971: pl. 21 fig. 7.

Lituites toernguisti – Chen 1987: 77.

non Lituites tornquisti – Jaanusson & Mutvei 1953: text-fig. 3a.

non Lituites törnquisti – Neben & Krueger 1971: pl. 21 fig. 8.

Diagnosis

Species of the genus Lituites with coiled conch diameter of 16–20 mm; whorls contiguous but not in contact. Uncoiled part moderately curved, expansion angle of 3–5.5° in early growth stages and 7° in later growth stages; whorl height at maturity of ca 25 mm. Mature aperture with broad lateral sinuses and a deep ventral sinus; dorsolateral lappets not indicated by the shape of ornament elements (after Holm 1891 and Sweet 1958).

Type material

Not available for study; Holm (1891: pl. 1 figs 1–4) illustrated one specimen (reproduced here in Fig. 43A ), it is from Sollerön (Dalarna, Sweden), Red Lituites Limestone ( Lituites tornquisti Zone, Segerstad Limestone , upper part of the Upper Red Orthoceratite Limestone, Aseri Regional Stage, middle Darriwilian, Middle Ordovician).

Material examined

GERMANY • 1 spec.; Brandenburg, Niederfinow; Ordovician, Upper Red Orthoceratite Limestone; Neben Coll.; MB.C.30532 • 3 specs; Brandenburg, Niederfinow; Ordovician, Upper Red Orthoceratite Limestone; Neben and Krueger Coll.; MB.C.30533 to MB.C.30535 .

Description

Specimen MB.C.30533 ( Fig. 43C ) is a fragment of a coiled part (last half of a coiled volution preserved) and a short part of the moderately curved backcoiled part (length = 20 mm; wh = 12.4 mm; EA ~ 4°) of a conch with a compressed whorl profile (WWI = 0.85). The shell surface is weathered but coarse annuli are well-discernible even in the coiled part of the conch; just behind the coiled part of the conch, fine lirae or growth lines are preserved between the annuli.

Additional information about the ornament is provided by the specimens MB.C.30532 ( Fig. 43B ) and MB.C.30534 ( Fig. 44 ), which have coarse, prorsiradiate annuli and lirae; the elements form a relatively deep and sharp ventral sinus, while the lateral sinus and dorsal projection are not developed.

Remarks

Specimen MB.C.30533 corresponds to the species description given by Holm (1891) in the very small dimensions, the low expansion angle of the backcoiled part and a relatively coarse ornament. The other three specimens differ in larger expansion angles (5.3° in MB.C.30534, and 5.4° in MB.C.30532 and MB.C.30535), but they are also assigned to L. toernquisti here, since they correspond to specimen MB.C.30533 both in size and ornament.

On the contrary, specimen MB.C.30568 ( Neben & Krueger 1971: pl. 21 fig. 8) and also the specimen figured by Jaanusson & Mutvei (1953: text-fig. 3a) are not included in L. toernquisti here because they

are much larger in overall proportions (diameter of the coiled part ~ 30 mm) and have greater expansion angles (7°).

Lituites toernquisti may be difficult to distinguish from Trilacinoceras discors when the body chamber is not completely preserved. However, L. toernquisti belongs to Lituites because it possesses a fivelappeted aperture ( Fig. 43A ), i.e., not three-lappeted as is diagnostic for Trilacinoceras (for further discussion, see Holm 1891; Sweet 1958; Aubrechtová & Meidla 2020). Lituites toernquisti differs from other species of the genus Lituites chiefly by the small size of its conch (coiled part diameters up to 20 mm, whorl height at maturity about 25 mm). The only exception to this is L. baculus sp. nov., which is comparable in overall size to L. toernquisti ; however, the coiled part in the former species is composed of only 1.5 rapidly expanding volutions and the shell ornament is different (annuli in the coiled part are absent and ornament elements in the backcoiled part have prorsiradiate direction).

Geographic and stratigraphic occurrence

Sweden (in situ) and northern Germany (in erratics within Pleistocene gravels); Aseri and possibly Lasnamägi regional stages, Darriwilian, Middle Ordovician.

Lituites toernquisti is a stratigraphically significant species in the Upper Red Orthoceratite Limestone of Baltoscandia indicating the late Aserian Lituites toernquisti Zone ( Jaanusson & Mutvei 1953; Evans et al. 2014).

Figures

Fig. 43. Lituites toernquisti Holm, 1891 from the Upper Grey Orthoceratite Limestone. A. Reproduction of the illustration by Holm (1891: pl. 1 figs 1–3); from left to right – lateral, dorsal and ventral view of specimen (mature aperture). B. Specimen MB.C.30532 (Neben Coll.) from Niederfinow (Brandenburg); previously figured by Neben & Krueger (1971: pl. 21 fig. 7); lateral view of specimen. C. Specimen MB.C.30533 (Neben & Krueger Coll.) from Niederfinow (Brandenburg); lateral view of specimen. Scale bar units = 1 mm.

Fig. 44. Lituites toernquisti Holm, 1891 from the Upper Grey Orthoceratite Limestone; lirae in specimen MB.C.30534 (Neben & Krueger Coll.) from Niederfinow (Brandenburg), at wh = 11 mm. Scale bar units = 1 mm.