I'm designing the crab claws to go with the crab project. My plan is to have a flexible arm, similar to the trunk on the Flexiphant. The claw will be closed using the same tendon that bends the arm.

Here's a first draft. The smaller part of the claw, at the top of the picture, is fixed to the arm. The larger part of the claw falls open under its own weight. 

The tendon is fixed to the inside of the larger claw then threaded through each of the arm sections. 

When the tendon is pulled the claw closes and the arm bends upwards.

I need to modify the arm sections so that they stick out horizontally like this when the tendon is relaxed.

Pull the tendon and the arm raises like this. Another arm on the other side, a set of legs and a scotch yoke to drive everything – all together should make a rather fun model!