New information on two jawless vertebrates from the Middle Devonian (Eifelian) Orcadian Basin of Scotland

Two Middle Devonian (Givetian) jawless fish, Cornovichthys blaauweni Newman & Trewin, 2001 and Achanarella trewini Newman, 2002 are redescribed based on new material. It can now be demonstrated that C. blaauweni has paired anal fins and a median lobe of the caudal fin. This indicates a close relationship to the Late Devonian (Frasnian) jawless fish Euphanerops longaevus Woodward, 1900. Cornovichthys blaauweni is shown to have possessed a short nasohypophyseal system (olfactory organ) supported by two supporting rings, the anterior of which supported a solitary nasohypophyseal aperture (nostril). Achanarella trewini is shown to be a distinct species to C. blaauweni, which is in the same size range for the largest individuals. Achanarella trewini possessed no anal or dorsal fins with only a caudal fin and possibly paired lateral fin folds. The snout is unusual being place quite far forward of the branchial basket. At the anterior end is a short nasohypophyseal system with a large nasohypophyseal aperture with four barbels surrounding it.