Trachyplax

Larsson, Cecilia M., Peel, John S. & Högström, Anette E. S., 2009, Trachyplax arctica, a new multiplated problematic fossil from the lower Cambrian of North Greenland, Acta Palaeontologica Polonica 54 (3), pp. 513-523 : 515

Genus Trachyplax nov.

Type species: Trachyplax arctica sp. nov., by monotypy.

Etymology: From Greek trachy, rough; plax, plate.

Diagnosis.—Large (up to 19. 3 mm), robust, calcareous sclerites growing by marginal accretion; external surfaces display concentric growth lines encircling the elevated apex and radial ridges originating from the apex and spreading over parts of, or the whole, sclerite, surface (new ridges being introduced between older ones). Eight sclerite types identified (A–H, see below) of which A is selected as the defining element: it is bilaterally symmetrical in presumed dorsal view, divided into an oval shield and an elongate, subrectangular rostrum, but strongly arched in lateral perspective.

Discussion.—The nature and form of the scleritome is not known. The holotype of the type species, and thus the defining element of the new genus, is selected from the most distinctive and most abundant sclerite morph, type A; all elements are described below.

Stratigraphic and geographic range.— Trachyplax arctica is currently known only from the Paralleldal Formation (Cambrian Series 2, Stage 4) of Paralledal, southern Peary Land, North Greenland.