Silurian cartilaginous fish

Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes). They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and chimaeras. Acanthodians possess a mosaic of features shared with both osteichthyans (bony fish) and chondrichthyans (cartilaginous fish). In general body shape, they were similar to modern sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteians (gars, bowfins).

Nostolepis is an extinct genus of acanthodian fish which lived from the Silurian (Wenlock) to the Middle Devonian (Givetian). Members of the genus include Nostolepis gracilis and Nostolepis striata.