Marine invertebrates can add color to the bottom of your aquarium and many provide beneficial cleaning abilities to reducing maintenance required. Shrimps are mostly the scavengers that will look for any excess food that is on the bottom substrate, will consume any dead fish before other fish can eat them, and can also clean up some algae. Snails on the other hand are mostly used for their algae eating abilities on the aquarium's walls and mixing up the substrate used. Clams can be used to clean up any excess algae or waste that is found inside of the water column, although they are not ideal for a vast majority of aquariums. The major challenge is to make sure that the given invertebrate is compatible with the fish you wish to keep, as their environment requirements can be vastly different and may result in a fatal situation. By understanding what exact species that you intend to keep and care for, you can provide a environment that is similar to their natural environment and watch them behave how they would in the wild.