Lituites clavis, 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 : 79-80

Lituites clavis sp. nov.

urn:lsid:zoobank.org:act:717047ED-9C20-4AE7-B9F8-33C72291029F

Figs 58A , 59 , Tables 9–10

Lituites sp. Neben & Krueger 1971: pl. 31 fig. 3.

Diagnosis

Species of the genus Lituites with coiled part ca 34 mm in diameter; three tightly coiled whorls; whorl expansion rate ~ 2.00. Backcoiled part moderately curved, expansion angle ~ 2°. Shell surface in the coiled part with annuli and growth lines and in the uncoiled part with very flat annuli a lirae. Ornament elements in the uncoiled part prorsiradiate.

Etymology

From the Latin ‘ clavis ’ (nomen) = ‘a key’, referring to the shape of the holotype.

Type material

Holotype GERMANY • Brandenburg, Niederfinow; Ordovician (late Lasnamägi Regional Stage, late Darriwilian), Upper Grey Orthoceratite Limestone; Neben Coll.; MB.C.30537 (illustrated in Fig. 58A ).

Description

Holotype MB.C.30537 ( Fig. 58A ) consists of the nearly complete coiled part (dm = 34 mm; three tightly coiled volutions; WER = 1.90; Fig. 59 ) and the moderately curved backcoiled part (length = 100 mm; wh = 16 mm; EA ~ 2°). The ornament undergoes some ontogenetic change: (1) Up to 20 mm diameter of the coiled conch, annuli are the dominant ornament element; these are particularly coarse and sharp on the inner half of the flank. They stand at distances of about 1 mm and carry fine growth lines that are strengthened to sharp lirae on the crests of the annuli. Between the crests of the annuli, the growth lines are extremely fine and have distances of less than 0.1 mm. (2) On the last half whorl of the coiled part, the annuli become significantly weaker and are only recognisable as low undulations. The growth lines are now stronger and stand at distances of about 0.15 mm. They are periodically raised to sharp lirae at intervals of about 1 mm. (3) The backcoiled part of the conch shows some remains of the shell with lamellar radial elements. These are flat annuli (3–4 mm apart) and irregularly placed, flat lirae at distances of 0.5–1.0 mm; both ornament elements leave a faint impression on the internal mould. Lateral sinus is shallow, ornament elements in the uncoiled part are prorsiradiate. The ventral sinus is moderately deep and rounded. The chamber length declines from CLR = 0.50–0.23 during ontogeny.

Remarks

Lituites clavis sp. nov. has a relatively large coiled part, which consists of as many as three volutions. In these characters, the new species is similar to Trilacinoceras knoefleri sp. nov., which differs in the finer shell ornament and a greater expansion angle. Since the mature aperture is not preserved in L. clavis sp. nov., it cannot be decided whether the species is indeed a Lituites or a Trilacinoceras . However, the rather coarse shell ornament and the circular whorl profile of the backcoiled part of the conch justifies the classification of L. clavis sp. nov. in the genus Lituites .

Lituites clavis sp. nov. differs from L. lituus by a greater diameter of the coiled part (34 mm but only up to 30 mm in L. lituus ) and a lower expansion angle of the uncoiled part (2° but 5°–8°in L. lituus ); in addition, the annuli at the backcoiled part in L. clavis sp. nov. are flat, not prominent as in L. lituus . Lituites clavis sp. nov. differs from L. procerus because its coiled part is larger in diameter (34 mm but only up to 30 mm in L. procerus ) and its uncoiled part is moderately curved slightly curved or straight in L. procerus .

Figures

Fig. 58. Species of Lituites from glacial erratics. A. Lituites clavis sp. nov., holotype MB.C.30537 (Neben Coll.) from the Upper Grey Orthoceratite Limestone of Niederfinow (Brandenburg, Germany); previously figured by Neben & Krueger (1971: pl. 31 fig. 3). B. Lituites dewitzi sp. nov., holotype MB.C.30538 (Neben Coll.) from the Schroeteri Limestone of Boltenhagen near Gross Klütz Höved (Mecklenburg-Vorpommern, Germany). C. Lituites nebeni sp. nov., holotype MB.C.30541 (Neben Coll.) from Upper Grey Orthoceratite Limestone of Niederfinow (Brandenburg, Germany); previously figured by Neben & Krueger (1971: pl. 31 fig. 2). Scale bar units = 1 mm.

Fig. 59. Lituites clavis sp. nov. A. Outline of coiled conch part of holotype MB.C.30537. B–E. Conch proportions and coiling rates of holotype MB.C.30537. Scale bar units = 1 mm.