I do suggest they have seashell hats as headdress, but not as a thing part of their body, though. Also coconut crabs are terrestrial crabs, they only spend time in the water as larvae before moving onto land for the greater part of their life.
Because people are so awesome and decided to help out with the race I've updated the OP with some new stuff. Check the OP for the new content! Weapon art by Sabre http://community.playstarbound.com/index.php?members/sabre.56279/ Majority of writing by Chamomileable http://community.playstarbound.com/index.php?members/chamomileable.46631/ Thanks guys, I might work a little a bit more on this idea if it gets a little more attention.
We would all love to play as a crab but the crystal thing is overused. Many other races like the Drale have crystals in their story. I suggest a giant waterless reef with scattered huts or something of the sort, but it's your decision. But otherwise I love this space-fareing roman crabs thing. 1 like for you!
Watch any documentary about crabs, and you will wonder whether they aren't already a space-faring exosuit biorobot race. They regenerate limbs, they shed their shells, they act very machine-like. Hell, if their arm or leg is hurt, they pluck it out and wait for a new one to grow. Arthropods are probably the closest to what we'll see of an alien organism in our lifetimes. I'd very much welcome a no-nonsense crustacean machine race that is feared by other Starbound races for their brutal efficiency. Wonder would it be possible for Chucklefish or anyone to add a multipedal race with their own armor, equipment, special abilities and animations. So far every race feels like a little more than a mere reskin of one bipedal species. I crave for some serious sci-fi diversity since Master of Orion days.
Those are Tachidi, Insecta subspecies from generally unloved Master of Orion III (it was radically different compared to first two installments). In my case however, it was my first turn-based space game which I played on and off over several years until I understood it well enough to enjoy it. Its interface, lore, steep learning curve and brutally serious tone, still hold a place in my heart.
So, the theme of these guys is Roman/Greek, then? I really like this suggestion. A lot of races seem to be trying to occupy the crystal niche as of late, though. They could use some more backstory.