Trilacinoceras knoefleri, Aubrechtová & Korn, 2022

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 : 89-92

Trilacinoceras knoefleri sp. nov.

urn:lsid:zoobank.org:act:F32CE3ED-2AF5-4959-9E5D-B97ECB7AB8B4

Figs 66C–D, 67–68, Tables 12–13

Diagnosis

Species of the genus Trilacinoceras with coiled conch 38 mm in diameter; 2.50 to 3 tightly coiled volutions; whorl expansion rate ca 2.30. Whorl profile compressed in coiled part, weakly compressed or almost circular early after uncoiling. Backcoiled part moderately curved, expansion angle 2–5°; ventral side rounded. Shell surface with growth lines and raised lirae in the coiled part; wide, flat annuli and lirae present in the backcoiled part. Ornament elements slightly irregular in distance and thickness; in the coiled part rectiradiate, in the backcoiled part prorsiradiate. Lateral sinus shallow, located between the mid-flank and the ventrolateral projection. Ventral sinus wide and rounded.

Etymology

After Hans-Rudolf Knöfler (Museum für Naturkunde, Berlin), preparator and collector of the holotype.

Type material

Holotype

GERMANY • Brandenburg, Teschendorf (Löwenberg); Ordovician (late Lasnamägi Regional Stage, late Darriwilian), Upper Grey Orthoceratite Limestone ; Knöfler Coll.; MB.C.11658 (illustrated here in Fig. 66C).

Paratype

GERMANY • Mecklenburg-Vorpommern, Mukran (Sassnitz, Island of Rügen ); Ordovician , Upper Grey Orthoceratite Limestone ; Krueger Coll.; MB.C.30559 (illustrated in Fig. 66D) .

Description

Holotype MB.C.11658 ( Fig. 66C) consists of the almost complete coiled part (dm = 38 mm; 2.75 tightly coiled whorls; WER = 2.20; initial chamber does not appear to be preserved; Fig. 67A–E) and a portion of the uncoiled part (length = 87 mm; EA ~ 2°). The shell ornament is preserved along the whole length of the specimen. In the first 1.5 whorls, the ornament has fine growth lines and closely spaced annuli. In the rest of the coiled part, the shell bears growth lines (0.25–0.3 mm apart) and raised lirae (up to 1.7 mm apart) lirae. The lirae are rather irregularly developed, at conch diameters 24 mm and 28 mm, they are very fine and barely visible. In the backcoiled part of the specimen, wider and lower annuli (3 mm apart) appear; lirae are up to 0.5 mm apart. The distance of lirae increases during ontogeny, while the distance of annuli shows a decrease (up to about 7 mm wh) followed by an increase ( Fig. 68B–C). In the coiled part, the ornament elements are rectiradiate with a lateral sinus between the mid-flank and the ventrolateral projection, while in the backcoiled part, the ornament elements change into prorsiradiate and form a flat lateral sinus. Between coiled conch diameters 25 and 31 mm, the ornament elements are biconvex in shape.

Paratype MB.C.30559 ( Fig. 66D) consists of a coiled part (dm = 30 mm; 2.5 tightly coiled whorls; WER = 2.40; Fig. 67F–J) and a portion of the moderately curved backcoiled part (length = 45 mm; EA ~ 4.5°); the whorl profile is almost circular at the beginning of uncoiling. The chamber length can be measured near the end of the specimen, where the CLR is 0.48. The shell ornament is preserved along the whole length of the specimen, except for the innermost whorls. In the coiled part of the conch, it consists of growth lines and more or less regularly raised lirae (up to 1 mm apart). After uncoiling, the lirae become wider and very flat annuli appear (ca 3 mm apart); the lirae are up to 1 mm apart. The ventral sinus of ornament elements is broad and rounded ( Fig. 68A). The lateral sinus is shallow and located between the mid-flank and the ventrolateral projection. The dorsal sinus is very shallow.

Remarks

The aperture is not preserved in the specimens but they are assigned to Trilacinoceras because of the combination of a large coiled portion consisting of almost three whorls, the slowly expanding and moderately curved backcoiled conch part and ornament that changes from narrow annuli/raised lirae to wider annuli during ontogeny. Trilacinoceras knoefleri sp. nov. differs from the type species T. discors in the larger size and lower expansion angle. Also, the ventral sinus of the ornament elements is broader and the whorl profile in the uncoiled part of the conch is less compressed and ventrally not flattened.

Trilacinoceras knoefleri sp. nov. is very similar to T. cf. hunanense , which is, however, more finely ornamented along the whole conch length and has a greater expansion angle of the uncoiled part; T. hunanense possesses a straight uncoiled part of the conch.

Geographic and stratigraphic occurrence

Northern Germany (in erratics within Pleistocene gravels); late Lasnamägi Regional Stage, late Darriwilian, Middle Ordovician).