Video doesn't load, but from memory, this is the blue-ringed octopus, found in north Australian waters. Very small octopus with superb sand camouflage until it's disturbed, in which case the flashing blue rings warn that its saliva contains neurotoxins. Due to its size, the initial nip from its beak is nearly painless.

E: Video's back, I mistook north for south but was otherwise right. c: