Black
Because the crab wants to fight.
A black finger crab is another term for a reef crab, a crab of the family Menippidae, Latin name Ozius truncatus, which is endemic to parts of Australia and New Zealand.
it will appear by and underneath the aquarium
yes
it is a little crab robot with water inside of it
crab, hermit crab, and lobsterHermit crab is a kind of crab, and it doesn't actually has its own shell. Oysters have shell and lives in water.
Trilobite+sand=crab
They get oxygen from the water and air depending on what species of crab they are
Well, the water has oxygen in the water so yes, the blue creek crab can live under water forever IF it has too. It usually goes up for oxygen, but the oxygen in the water is a secondary source.
Well this sort of crab (the camouflage crab) I've researched it and it scavenge's all the dead particles in the water
Most likely your crab overheated. A crab needs tepid (not hot, not cold) water to bath in and drink from. It does not take long to heat a crab to death.
if they are black and tiny they are probably mites they are usually on the crab too