Yes Delgado is correct they are the Payaras that grow to 12". The Armatus species gets huge. The red tails get to 2 feet. 4 dollars each is definetly a mistake if you can get them for 4 get them all man great deal 65 each at my lfs! The only hang up is they will only eat live food guppies and feeder fish, hard to get them off live food.
He also told me that it'll get as big as a Common Pleco at 6"