One of the most popular invertebrates in the aquarium hobby. They have large antennae that extend for a few inches beyond their shells when fully grown. They can grow quite large in aquariums. The larger they get, the better job they do at cleaning algae. At a small size, I would recommend 1 per every gallon of water to help with algae concerns. As they grow, they can be kept one per 5 gallons as they approach gold ball size. There are a few colors to choose from!