The species identifier is the second word of every scientific name (scientific names are composed by always two words).
The first word in a scientific name describes the genus to which the species belongs to.
For example the scientifical name of the Iberian lynx is Lynx pardinus. Here, the word lynx refers to the genus it belongs to, and pardinus to that specific animal group that share the exact same characteristics (since not all lynx species share the same characteristics).
Given all that, you'll need two have only one name and one sirname, and your last name would be your "identifier".
Hope it helped,
Happy homework/ study/ exam!