A Creatures environment can determine how it will evolve, and in this sub-species of Giant Crabs case, it required two evolutionary traits; deception and intimidation. An extended mouth/neck mandible fooled coastal folk for centuries into believing this crab was an actual dragon, and actual dragons fooled as well! Dragons will not invade its shored-territories, thus creating a safe haven for its smaller cousins.
-note. the wings are purely aesthetics, and cannot function. perhaps if they’re modified through magic…
