Every different kind of organism called a species, and closely related species are grouped together into genera (the singular of with is genus). Each species has a two part scientific name, composed of its generic name and its species name. For example, the house fly, which belongs to the genus Musca, is scientifically known as Musca domestica. Where a number of members of the genus Musca are mentioned, later examples may be abbreviated to, for instance, M. domestica. By convention the genus name begins with a capital letter.
Related genera are grouped into families, related families are grouped into Orders, Orders are grouped into classes, and classes are grouped into phyla. The latter are the largest divisions of each kingdom. Family names in the animal kingdom always end in …idea, while plant families always end in ..aceae.