It was one of the first Thumtrac™ discs. For some reason it was freaky overstable for a lid; not sure why but it was. You could actually crank on one, which was weird for a lid. It wasn't as deep as a Birdie but felt deeper than a Polecat.
When the Rhyno came out, they retooled the Piranha using a Thumtrac™ more like the Rhyno top. The new disc wasn't nearly as stable as the old Piranha. The Rhyno had taken that overstable putter slot in the line-up anyway, so they made the new Piranha into the Birdie. They apparently had messed up the old Piranha mold in the process, so the Piranha went OOP.
At the time that they were around, I really didn't like them. Now I wish I could try one again.