The biological 'job' of shrimp in water is to feed on organic matter such as dead plant materials, bacteria, and dead animals as mostly invertebrates - organics . On land, cockroaches feed on dead leaves, garbage, and other refuse. Both animals are detritivores, and they fill the same niche in different environments.
Niche of an organism refers to its habitat, activity role and functional position within system. Detritivores are the organisms that feed on dead and decaying organic matter and serve to release the nutrients back in the environment. Since both shrimp and cockroach feed on dead and decaying organic matter, both are detritivorous. Being found in different habitats, they fulfill the same niche (same functional role, that is, the role of detritivore) in different environments.
Here is a very good description of detritivore
https://biologydictionary.net/detritivore/Very good grass shrimp facts and information in these links:
https://www.tankfacts.com/invertebrates/freshwater/shrimp/grass-shrimp_166https://www.jstor.org/stable/2680196
