If you like small elusive crabs, the Porcelain Crab - Petrolisthes spp - fits the bill. The white ones tend to reside near or in an anemone, using the anemone's tentacles for protection. The crab has pinchers and can catch meaty foods, but it also has twin fans that it holds out to trap particulates floating by. A clownfish may tolerate this neighboring crab, but this depends on the fish's territorial attitude. These crabs can be tough to locate in a bigger tank, and once discovered elicit a smile for sure.
In this picture, the Porcelain crab is hosting in an orange rock anemone, which is a very sticky creature. Somehow these crabs don't get stuck, nor do they get eaten by their hosting neighbor.