Hook Saltwater hook (Gamakatsu SL11-3H or similar), 2-6
Thread Tan GSP 100 or 210 denier
Materials
Claws/legs Rubber or silicone legs and craft fur (several)
Body Flexi/body tubing tied at both ends (1 length)
Eyes Mono or bead-chain, weighted to match depth (1 pair)
Flash A few strands of pearl or tan flash (sparse)
How to tie it
Start thread at the bend. Tie in a splayed bunch of rubber legs and a wisp of craft fur to form the claws and trailing legs.
Tie in a length of hollow body tubing at the rear, over the claw base.
Advance the thread to the eye. Pull the body tubing forward, tie it down at the front, and secure both ends so the tubing balloons into a hollow, light, realistic crab body; the hollow tubing makes it land softly and sink slowly.
Add a few strands of flash and additional rubber legs at the sides for triggering movement.
Tie in weighted mono or bead-chain eyes to control the sink rate for the depth you are fishing.
Whip finish, cement, and trim the body tubing to a compact crab shape.