The L stands for Loricariidae, incidentally. There's a C number system, too, for Corydoras. Whether it stands for Corydoras or the family Callichthyidae or the subfamily Corydoradinae, I do not know.
It's perhaps worth mentioning what professional scientists do when they discover new species and before the beast is given a name. They don't use anything like L or C numbers, but instead use things like Corydoras sp. nov., where the "nov" stands for novum, i.e., "new" in Latin. You will also quite commonly see something like Corydoras sp. A, Corydoras sp. B, etc., where there are long lists of new species.
Another common occurence is to use Corydoras sp. aff. palaeatus or Corydoras sp. cf. palaeatus. The "sp. aff" means affinis and implies the specimen has affinity with, but you are sure it is not identical to, Corydoras palaeatus. The "sp. cf." means confer and implies that you are fairly sure it is the same thing as Corydoras palaeatus, but you (or science generally) needs to conduct further study to be 100% sure.
Aquarists get these two muddled up all the time, and will talk about Panaque sp. cf. nigrolienatus such as L027a and L330, for example, as being a different species to Panaque nigrolienatus, L190. Accordingly to their Latin names, the discoverers of those different L numbers are fairly sure they are all the same species and believe that the physical differences between them are down to differences in populations. Anything "sp. aff." on the otherhand really is a new species, albeit it one closely related to something already recognised.
Cheers,
Neale
(PS. Please note that you don't italicise the "sp.", "aff.", or "cf." when writing these names.)
