Zebrafish. This little fish is a vertebrate, and a relatively complex one. Looking at the major neurotransmitters and hormones that are investigated in neuroscience, they are as good of a model as many mammalian species.
Often in animal research, animals with a certain genetic alteration are compared to a “wild-type”. One might assume that there is no differences between wild-types, but many different strains of wild-type animals are used.