And heterostracans, osteostracans and placoderms have been found in both salty AND fresh water environments.

在咸水和淡水环境中都发现了 heterostracans、osteostracans 和 placoderms。

Because, osteostracans are among the few jawless fish to have a bony internal skeleton, or endoskeleton.

因为，osteostracans 是少数具有骨质内部骨骼或内骨骼的无颌鱼之一。

And scientists have seen signs of those changes in the armor of heterostracans, osteostracans and placoderms.

科学家们已经看到了异类动物、骨类动物和盾皮动物的盔甲发生这些变化的迹象。