Astraspis is a species of jawless fish from the Ordovician period adout 450 mya. Astraspis is 6 in long and it's head was covered in plates.
Description[]
In Sea Monsters : A Walking with Dinosaurs Trilogy Nigel Marven uses a dead astraspis as bait to attract a sea scorpoin. It was identified as "an armor plated fish"