Lituites baculus, 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 : 75

Lituites baculus sp. nov.

urn:lsid:zoobank.org:act:4683F88A-1A93-436C-87E0-6A8E2996F9A8

Figs 54A , 55 , Tables 9–11

Diagnosis

Species of the genus Lituites with a small coiled part (ca 21 mm in diameter); 1.5 tightly coiled volutions (only the last half volution slightly detached). Whorl expansion rate 2.70. Uncoiled part weakly curved, expansion angle 4°. Shell ornament with rectiradiate lirae in the coiled part and lirae (up to 0.5 mm distance) and annuli (up to 4 mm apart) in the uncoiled part. Ornament elements in the backcoiled part prorsiradiate with shallow lateral sinus.

Etymology

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

Type material

Holotype SWEDEN • Island of Öland , Gärdslösa; Middle Ordovician; Bottke Coll.; MB.C.29654 (illustrated in Fig. 54A ).

Description

Holotype MB.C. 29654 ( Fig. 54A ) consists of the complete coiled part (dm = 20.8 mm; 1.5 tightly coiled volutions, of which the last half volution is slightly detached from the preceding; WER ah = 2.70; Fig. 55 ) and the weakly curved backcoiled and straight parts (length = 110 mm; wh = 15.6 mm; EA ~ 4°). The whorl profile is compressed (WWI = 0.88). The initial chamber of the phragmocone is 0.46 mm in length and the whorl height at the first septum is 0.94 mm. The ornament is rather coarse and regular. In the coiled part, only transverse, rectiradiate lirae are visible (<0.5 mm apart). In the backcoiled and straight part, coarse annuli are added and are up to 4 mm apart with lirae of up to 0.5 mm distance; the ornament elements are prorsiradiate with a shallow lateral sinus. The chamber length ratio is ca 0.44 and increases during ontogeny.

Remarks

Lituites baculus sp. nov. is most similar to Lituites toernquisti because of the small overall size, the weak curvature of the backcoiled part and relatively low expansion angle of the backcoiled part. However, the new species has only 1.5 volutions, which expand rather rapidly (WER 2.70). The shell ornament is also different: L. baculus sp. nov. lacks annuli in the coiled conch part and in the backcoiled part, the ornament elements have prorsiradiate direction.

Figures

Fig. 54. Species of Lituites from the Middle Ordovician of Gärdslösa (Island of Öland, Sweden). A. Lituites baculus sp. nov., holotype MB.C.29654 (Bottke Coll.). B. Lituites bottkei sp. nov., holotype MB.C.29651 (Bottke Coll.). Scale bar units = 1 mm.

Fig. 55. Lituites baculus sp. nov. A. Outline of coiled conch part of holotype MB.C.29654. B–E. Conch proportions and coiling rates of holotype MB.C.29654. Scale bar units = 1 mm.