poorly defined; symmoriids are thought to lack a spine-brush complex but are otherwise identical to stethacanthidae. Stethacanthids are identified by the presence of a spine-brush complex, which is in some cases non-existent (e.g. juvenile males), making the certain classification of stethacanthids and symmoriids difficult. More recently, Symmoriida as a whole has been reclassified as part of Holocephali, meaning that Stethacanthus is more closely related to modern chimaeras than to sharks. See also Stethacanthidae Symmoriiformes Akmonistion References External links Symmoriiformes Paleozoic fish of Europe Devonian fish Carboniferous fish Paleozoic fish of North America Fossil taxa described in 1889