They actually belong to many different families. Lorricaidea is one identification group. Another is the "C" numbers such as the Corydorus.(Sorry for the spelling) Nepherael is correct that there are thousands of different species. So they are grouped according to an "L", "C", etc classification. Identification is done thru a DNA breakdown to be able to properly identify a family and species.
Don't be fooled by appearances. Different species within a group can be 20 inches and other can be only 4 inches. When you see a major subspecies they are usually identifies as sp. Sp usually mean it belongs to a major species group but individual group has not been classified. You could have a ancistrus (bristlenose) sp which means the bristlenose (Ancistrus) is the parent family and further subspecies is not identified, such as albino, as a unique subspecies.
Researchers and scientists are trying to clean up the numbering system as it is very confusing and not always accurate. Sometimes a species has been known to be identified in more than one class.
I know this is not a clear answer, but I hope it gives you a general idea.