Arthrotheriformes

Arthrotheriformes are the ancestral, primarily oceanic arthrotheres. Like other arthrotheres, they have articulated legs, fused gonopodia, and beak-like jaws.

Family Arthrotheriidae
Benthic arthrotheres which walk about on the ocean floor.

Family Crocoscorpiidae
Pelagic, predatory, Eurypterid-like arthrotheres.