We're talking about two very different fish here, so be careful Olympia.
The
Twig Catfish is likely Farlowella vitatta. The
Whiptail Catfish may be
Rineloricaria parva. Both are in our profiles with photos, click the shaded names.
Another danger concerns both of these common names, which can be applied to various species that are themselves very different. The two in our profiles are the smaller species and suited to a 20g. But the others, such as Royal Farlowella and Royal Whiptail and various other names get much too large for a 20g.
Also, note the water parameters. The Whiptail is fine is slightly acidic to slightly basic, and I suspect this is the fish 1077 had in mind. The Twig is wild caught and must have soft acidic water or it will not last. I have both of these, and have raised some fry even from my Farlowella and they are now adults. One of my favourite fish, but highly sensitive to water parameters and quality.
Byron.