Rhynchorthoceras rugium, 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 : 24-25

Rhynchorthoceras rugium sp. nov.

urn:lsid:zoobank.org:act:3285F969-0E64-45B9-87BA-52BECCB14B9E

Fig. 15A , Table 2

Diagnosis

Species of the genus Rhynchorthoceras with an expansion angle of 10°; whorl profile circular. Shell surface with transverse striae, which are arranged conspicuously far apart from each other (up to 4 mm at wh = 22 mm), distance increasing more or less regularly during ontogeny. Striae oblique but straight laterally, directly transverse and straight ventrally, with a low projection dorsally.

Etymology

From Rugia, the Latin name of the Island of Rügen, from which the holotype originates.

Type material

Holotype GERMANY • Mecklenburg-Vorpommern, Mönchgut Penninsula (Island of Rügen); Ordovician, Upper Red Orthoceratite Limestone (Kunda Regional Stage, middle Darriwilian); Hoffmann 1972 Coll.; MB.C.11728 (illustrated in Fig. 15A ).

Description

Holotype MB.C.11728 ( Fig. 15A ) is an orthoconic but apically weakly curved phragmocone of 125 mm length. At its maximum whorl height of 22 mm, the conch has a circular cross section; the expansion angle is 10°. The shell ornament is preserved in more than half of the specimen and consists of transverse striae. The distances of these increase gradually along the conch and stand conspicuously far apart (up to 4 mm). Only at a whorl height of 18 mm, the striae stand closer together. They extend in oblique direction with straight course across the flanks and are straight on the venter; on the dorsum they form a low projection.

Remarks

Rüdiger (1889) was the first to recognise striated forms of Rhynchorthoceras and considered them as representing a separate species. Patrunky (1926) named these forms R. ruedigeri but did not provide any further description or figures. The name Rhynchorthoceras ruedigeri is thus a nomen nudum and two striated species of Rhynchorthoceras are newly defined here (see also the text below).

Rhynchorthoceras rugium sp. nov. might be confused with R. angelini (described above), if lirae in the latter are very flat or poorly preserved. However, the ornament elements are apparently more widely spaced in R. rugium sp. nov. The other striated species, R. kranepuhlense sp. nov. (described below), differs from R. rugium sp. nov. in its finer, more irregularly spaced striae; furthermore, the conch is locally slightly constricted in R. kranepuhlense sp. nov.

Figures

Fig. 15.Species of Rhynchorthoceras from the Upper Red Orthoceratite Limestone.A. Rhynchorthoceras rugium sp. nov., holotype MB.C.11728 (Hoffmann & Gager 1972 Coll.) from Mönchgut (Island of Rügen); lateral, dorsal and ventral views. B. Rhynchorthoceras kranepuhlense sp. nov., holotype MB.C.11730 (Kummerow Coll.) from Kranepuhl (Brandenburg); ventral, lateral and dorsal views. Scale bar units = 1 mm.