from what I understand, Loricaridae (aka Suckermouth Catfish) is the name of an entire family of fish that encompass the smallest otocinclus to the mammoth plecostomus. Also, from what I understand, the L prefix for plecos is an abbreviation of the family Loricaridae, and the L-number is a substitute for taxonomy until the scientific community has a chance to catalog the variety of species in existence.
perhaps the store was just too lazy to give you the proper name of the fish...