Antiarchi

The Antiarchi "Opposite anus" is an order of heavily armored placoderms. The antiarchs were the second-most successful group of placoderms (after the arthrodires) in terms of numbers of species and range of environments.  

The front part of their bodies were heavily armoured. The rear parts were sometimes scaled, sometimes naked. The pectoral fins were modified.  In primitive forms, such as Yunnanolepis, the limbs were thick and short, while in advanced forms, such as Bothriolepis, the limbs were long and had elbow-like joints. Probably they helped the fish pull themselves across the substrate, or allow their owners to bury themselves into the substrate.

 References 

 Other websites 
 Review of Antiarcha at Paleos

Category:Fossils
Category:Placoderms