Skill level, experience, budget, time, what must it do lots of information needed before anyone can do much other than suggest google yourself.
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Websearching "robotic arm" or "robotic hand" (or maybe "remote handler" or "remote manipulator") is more likely to find designs than "robotic claw" would be.
step 1: make a robotic claw step 2: attach it to your rov. Your design constraints are vague. I presume it has to be waterproof... degrees of freedom of movement/how articulated it is makes a difference... directly controlling joints, or keeping the actuators in the waterproof section while using cables to transfer mechanical strength is an option.