High Quality Content by WIKIPEDIA articles! Rhenanida ("Rhine (fish)") was an order of primitive, lightly armored (relatively speaking) placoderms. Unlike most other placoderms, the rhenanids` armor was made up of a mosaic of unfused scales and tubercles. This "mosaic" corresponds to the plates of armor in other, more advanced placoderms, suggesting that the ancestral placoderm had armor made of unfused components, as well.