Arthrotheria

Arthrotheria, better known as Arthrotheres, are a class of hexapodal arthropod-like organisms with articulated legs, fused gonopodia, and beak-like jaws They are a large, diverse clade which has representatives in the ocean and on land.

Order Arthrotheriformes
The ancestral group of Arthrotheres, which are generally predatory and fully aquatic.

Order Bistratiformes
Often terrestrial or amphibious Arthrotheres which posses both an endoskeleton and an exoskeleton.