Halimeda algae is a smart object to mimic since very few organisms enjoy dining on this hard algae.
To be honest, H.heraldica cheats a little bit with its camouflage. This species is a decorator crab; The halimeda crab attaches rigid fronds of halimeda algae to its rostrum (the forward extension in front of the eyes) to enhance its camouflage. It really appears as if giant green calcareous horns are growing out of the crab’s head.
But the rest of its green, halimeda-like carapace is au naturel. Simply awesome!