Ischnacanthiformes

Ischnacanthiformes is a prehistoric order of "acanthodian" stem-chondrichthyans found in Canada, Ukraine and United Kingdom. Members of this order were nektonic carnivores, eating animals that swim rather than plankton. They had slender builds, light armor, deeply inserted spines, shark-like teeth, and two dorsal fins. Some species were around 2 meters (6.56 feet) long. It was described by Berg in 1940.

Ischnacanthus is an extinct genus of acanthodian jawed fish. It lived from the Pridoli to the Lochkovian. The type species I. gracilis is only known from Lochkovian.