The product of Genetic engineering, these Tribbles are sterile and will not breed. Note the Blond time travelling Tribble. This Tribble belonged to one Cynthia Jones , who participated in "The Big Game" at Quarks, several years before Tribbles were officially re-introduced to the time line

Sponge

Crystal

Satin

Fungus

Mineral

Mica

Spindle Crystal

Floating Sponge

Time Traveler.

And here we have the rare Hairless Tribbles, sometimes referred to as "Picard's".