The most common type of tail type you will ever come across in pet stores is the Veil Tail. This type of tail is

Veil Tail Betta
Screen shot 2011-03-13 at 1.11.58 AM
Originated From: Thailand
Approximate Petstore Cost: $3.00
Fin Type: See Below
long, with a long anal and dorsal fin also, and droops down from the caudal peduncle. In breeding, a veil is dominant over other tail types and is therefore undesirable when breeding show Bettas. The term "veil tail" is often abbreviated to "VT". Veil Tails are now no longer accepted in the show Betta circuit due to their bloodlines being diluted by excessive breeding for the pet store market.

(Taken from here)

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