stonefish
the stonefish look like a stone, just like the reet that it live on. it also likes to sit on the sandy seabed. it has spines, though, that it uses to defend itself. they are very sharp and contain a nasty venom which can be very painful and sometimes lethal.
to avoid the stonefish's nasty sting, you mustn't touch the reef while swimming and you should make sure you always wear shoes or sandals when walking in shallow, sandy water.