Antiarchs (the Antiarchi) were a type of (mosty) small placoderms that were abundant during mid- to late-Devonian. These armored fish ranged from 8-12 inches (20-30 cm) long. Instead of the pectoral fins that other fish have, these unusual tetrapods had segmented 'arms' that were covered by hard dermal bone, but these arms lacked an internal skelet
Found on http://www.enchantedlearning.com/subjects/dinosaurs/glossary/
Antiarchi (`Opposite anus`) is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments. The order`s name was coined by Edward Drinker Cope, who, when examining some fossils that he thought were armored tunicates relat...
Found on http://en.wikipedia.org/wiki/Antiarchi
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