A VT only has two ray's so you have to know about ray's. Here's one of my explanation for ray's: http://www.bettafish.com/showthread....39#post2613201
As I state there, VT's have only two ray's and usually are more rounded or sort of pointed. VT is the classic droopy tailed Betta's and the females tend to look similar to their male counterparts. Here's a classic VT girl,
Here's a better more exaggerated example. This is a long finned girl and you can really see the two ray's.
And more so here
And this is a traditional Plakat girl, notice how the ray's stick out from the webbing on her tail fin. That's one trait of a PK, however sometimes a VT can have something similar if there was a Crowntail in it's gene line. Also note how thick and streamline she looks compared to the two VT's above. (Note the red VT is also eggy, that's why she's so fat)
Next "step" up is Delta and Super Delta. Delta's, of course being a triangle in geometry is similar in Betta tails. A Delta cannot reach the 180 degrees that a Halfmoon can but anything underneath and has MORE than 2 ray's. So 4 ray's or more and underneath 180 degree's is a DeT. This is one of my girl's aquabid picture, in the middle area of the end of her tail you can see that she's got four ray's making her a Super DeT since she almost reaches 180, but not quite.
Now Halfmoon's HAVE to get up to 180 degree mark or over (Over halfmoon; OHM) and can have anything from two ray's and more but aboslutely must get to the 180 degree mark to be considered HM. Here's an Aquabid picture which isn't mine. I do have HM girls but none have good enough pictures to show for an example lol She's about a 8-10 ray'd girl, hard to tell since it's not a close up. Notice the nice D shape of her tail.
Another Aquabid picture that isn't mine but you can see how her tail is straight up and down and makes the D shape, she's a Halfmoon.
And then of course you have your Crowntails which have varying degree's of angles, so some of them with poor breeding will have a tail like a VT and can't even get to a 100 degree mark. And then other's can actually get up at the full 180 degree mark. This girl is a Super DeT because she almost makes 180 but not quite.
The same goes for Double Tails (DT)
I believe I've covered the tail types, feel free to ask more questions ^_^