Acanthacanthus Valiukevičius, 2003a

Valiukevičius, Juozas & Burrow, Carole J., 2005, Diversity of tissues in acanthodians with Nostolepis-type histological structure, Acta Palaeontologica Polonica 50 (3), pp. 635-649 : 644

Genus Acanthacanthus Valiukevičius, 2003a

Type and only species: Acanthacanthus ornatus Valiukevičius, 2003a ; Severnaya Zemlya Archipelago , Spokojnaya River , outcrop 41, bed 12; Lower Devonian , Lochkovian, Severnaya Zemlya Formation .

Diagnosis.—Vesperaliid acanthodian with flank scales of a large size (> 0.7 mm wide), having elongated, rhombic, flat crown plate distantly extending well beyond the base posteriorly, low neck and deep base; one or two symmetrical pairs of the longest low, flattened radial ridges run towards the posterior crown tip; longitudinally depressed medial area contains one or two pairs of short, acute ridgelets forming a separate part towards the anterior crown edge. The oldest two growth lamellae of the medial area grew superpositionally whereas the succeeding ones (up to four) attached as areal growth zones along the lateral edges, thus increasing only the breadth of scale. Scale crowns are entirely composed of stranggewebe producing very long and dense stranglacunae; only the superficial layer of this tissue weakly resembles odontocytic mesodentine in the lateral growth zones, with outwardly oriented and longer dentine tubules; unique wide knot−like chambers characterize the vascular canals in the scale primordium and junctions of the ascending and circular canals in the growth lamellae of crowns.