Crabs are SF0 creatures that show up in GearHead 1 dungeons; they tend to be giant, and unfriendly. They are decently armored and have strong claws that can inflict a lot of damage to beginning adventurers, but they move at a low speed. Dead crabs are a source of sashimi.
In the ASCII version of GearHead 1, crabs show up as w.
Crab[]
Your typical giant crab.
Iron crab[]
Iron crabs are more heavily armored and so take longer to kill. Even using a high-DC weapon may require several hits.
They can be made into sashimi like ordinary crabs. Apparently only their armor is made of iron, not the tasty inside parts.