Meet the SherpaUW: a hybrid rover for subsea applications. It has 4 legs with 5 DOF and a 6DOF manipulation arm for prolonged missions on the sea floor. The joints on the legs and arm are sealed against water. The actuators are rated to a depth of up to 100m.
This robot can be used for surveillance, research on deep sea life, and other comparable missions. The above video shows it in action.