The sentinel oropede replaced its ancestor, the oropede. It no longer waits for creatures to die, it actively hunts them. It is an ambush predator who sit and waits for prey to swim by. When one does it will snatch it with its 6 "foot-mouths". Each leg has developed another joint, thus increasing the joints from 3 to 6 on each "foot-mouth" limb. It will eat iron in the rusty sands to help it grow its iron exoskeleton.
Its body shape has changes a lot to where all 4 eye stalks face forward looking from prey how they can still rotate around to see behind them. But when working together they can better focus on prey. They eyes themselves have also improved. They can see shapes now and not just light and dark. They cannot see in color. It can still use its many nostrils to sniff out dead prey.
Like their ancestors they will dig small aquatic burrows in the coastal sands. Their tails bud off small larva which will grow into adults as they eat iron. They can also reproduce via fragmentation if they get broken apart. As long as they have a leg with a mouth intact they can regrow their whole body. When they grow larger they will shed their old iron exoskeleton and then eat it for iron. New shells are gray while old have turned rusty-red.