Yes, Years ago, MANY years ago, I caught some baby crabs on the beach. My Dad took them home, and put them on a paper plate ( after they died ) and covered them with table salt. After a few months he simply brushed off the salt and glued them onto a stained board. They hung on the wall for years. Sounds simple, but maybe it will work for you.
We did Starfish that way also.
Salt dehydration and laquer are what they used to preserve the shell fish in my Biology Lab. Really simple procedure. Once the crab is dead, submerge it in a pail of salt...table, sea, kosher it doesnt really matter. the NaCl will break down the enzymes in the crab and cause some equilibrium changes that will extract all liquids from the crab. Id give it a month or so in the salt. After fully dried out brush off the salt and give it a coat of lacquer or gloss or something to protect the fragile shell and other limbs.
I am thinking of preserving some big carpenter Ants that are walking around my yard. Anyone with ideas let me know. I am thinking maybe a head down to the left mount and maybe one on a branch about ready to get sucked up by an ant eater..
i would inject the crab with a leg injection kit you can find at wasco.com .....
its a substitute for formaldyhide. otherwise you can freeze dry them..that is what many people do to preserve reptiles/amphibians, flowers, pets, or even restore wet paper.