Live foods!

I'm taking a piscicentric approach here: invertebrates are mainly food! Just ask any fish! Some of these food critters you can culture at home--— where you can, there's information on maintaining cultures here, as well as links. But you may also be interested in invertebrates for their own sakes: scope the "Invertebrates" folder to find snails and shrimps and other invertebrate visitors that live in the aquarium or that may appear there from time to time.

Some other invertebrates, which we ignore until they cause diseases, are in the "Health & Diseases" folder as Parasites.

Invertebrates also play major ecological roles in the food web.