Here are some possibilities:
* The Rainbow Runner: This is a fish, not a crab, with bright, iridescent colors, often found in tropical waters.
* "Rainbow Crab" as a nickname: Some colorful crab species might be called "rainbow crabs" by local communities or online forums. This could refer to any species with vibrant colors, like:
* The Blue Land Crab: Found in the Caribbean, this crab has bright blue claws and a colorful body.
* The Porcelain Crab: These small crabs have a variety of colors and patterns, including some with "rainbow" like hues.
* The Coconut Crab: These land crabs are large and have a colorful shell, though not necessarily "rainbow" in color.
To find out more, you might need to:
* Provide more context: What region or environment were you thinking of?
* Share a picture: If you have a picture of the crab, it might be easier to identify it.
Once you provide more information, I can help you find the specific crab you're thinking about!