Multi-chambered forms can have the chambers in a straight or curved line, can be spiralled or helical or even more complex. Ostracods are bivalved crustaceans and could be crudely described as being small shrimps in a mussel shell'. They live in freshwater and marine environments and are free-swimming or bottom dwelling. The type of microfossils you find can tell you a lot about the depositional environment. Foraminifera only live in marine or brackish water environments.
Some planktonic forams are indicators of water depth.
Some species of ostracod are very good indicators of salinity. The following paragraph originally appeared within the foraminifera graphic. Since it is not very clear ofn the scanned image it is reproduced below. Foraminifera are simple, one celled animals. They live in a test , which has one or more apertures , through which its ectoplasm can flow to be able to feed and move.