Darwin’s theory of evolution is incomplete; evolution by random mutation is a slow and precarious process. The leafy Sea dragon evolved into a seaweed shape for protective camouflage, to look a bit like seaweed might increase conspicuousness and be dangerous.
Leafy Sea dragon Phycodurus eques (on the left) and Seaweed (on the right).
With kind permission from Jeffrey Jeffords (Copyright), http://divegallery.com
The Indonesian-mimic-octopus is an even more unlikely creature of random mutation. Perhaps unsurprisingly undocumented until 1998 it transmogrifies into at least 17 different life forms. On meeting an enemy it metamorphoses into a creature unpalatable to that predator.