They're mostly shrimps but there are crabs and crayfish. Crayfish and crabs are not advisable to be mixed with fish. They will often eat and attack your fish and crabs are mostly brackish water.
If you want shrimps, there are cherry shrimps, Amano shrimps and bamboo shrimps.:thumbsup: They will not do well in soft water however as that makes their shells soft leaving them vulnerable to predation.