Acanthodes is an extinct genus of spiny shark

Acanthodii

Acanthodii is a class of extinct fishes, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans...

. Fossils have been found in Europe, North America, and Australia.

Compared with other spiny sharks, Acanthodes was relatively large, at 30 centimetres (11.8 in) long. The genus had no teeth, instead gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s. Because of this, it is presumed to have been a filter feeder

Filter feeder

Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...

, filtering plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

 from the water.

It also had fewer spines than many of its relatives. Each of the paired pectoral and pelvic fins had a spine, as did the single anal and dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

s, giving it a total of just six, less than half that of many other species.