I am trying to understand if there is any difference between the Otocinclus Affinis, the Otocinclus Arnoldi and the Otocinclus Sp.. Really I don't understand where is the difference between them, from the pictures they all look equal. The local pet store nearby has the Otocinclus Arnoldi one but they can't tell me if it is the same of the "Affinis" or the "Sp." (that, also, I have not idea what Sp. stands for...).
Any help and/or thoughts are very welcome!