Mollies belong to the family Poeciliidae. There are three common types;
Poecilia sphenops (common molly)
Your basic molly, seen in alot of pet stores across the globe. It's natural habitats range from the estuarine waters of Mexico through areas of Central America and into the waters of northernmost South America. Sphenops come in a variety of colors, including silver/white, black, marble/salt & pepper/dalmation (the interbreeding of silver & black mollies!), and goldust mollies (similar patterning of marbles mollies, with yellow or gold as the prominant color, with a speckling of black).
In addition to the different color strains, you can find sphenops with different fin shapes. Naturally, the finnage is a rounded tail fin and short dorsal fin, with the male's dorsal fin being slightly larger than the female's. Some "man-made" versions are the lyretail and balloon molly.
These mollies are peaceful, and do well in community tanks. You must keep in mind that mostly all types of mollies are normally used to brackish, warm waters, so be sure to add some aquarium salt to your tank!
Poecilia latipinna (sailfin molly)
The meaning in latin for this fish is "broad fin", indicative of the male's large dorsal fin, looking somewhat like a sail, and triangular in shape. :) Sailfins are much larger than the common molly, and tend to be a wee bit more aggressive. These fish come from the southeastern coasts of the United States, down and through the Yucatan peninsula of southeast Mexico. Here they enjoy the many variations of water from quite saline to completely fresh.
In the wild, sailfins are of an olive coloration, darker on top, lighter down below. The upper body flanks and dorsal fin are decorated with shimmering dots, and some males have an orange chest (possibly leading to the golden colored variety). Other colors you can find them in are varied, from solid black, silver, orange, marble, chocolate (black & orange mix!). I have even seen some with a pinkish cast to them (though they did look VERY strange!).
Poecilia latipinna are similar to the other sailfin molly, Poecilia velifera, and can be difficult to tell apart. Sailfins are beautiful fish, and an asset to any community tank!
Poecilia velifera (Yucatan sailfin molly)
The velifera are solely found in the yucatan Peninsula. Where the male latipinna's dorsal fin is triangular in shape, the male velifera's dorsal fin is rectangular in shape and can rise almost 2 inches above the spine. "Velifera" translates from latin to mean "carrying a sail". Combining this "sail" with it's large size, you get one impressive fish!
The Yucatan sailfin is the largest of the molly species. Males can grow to an upwards of 6 inches, while the females hit a lofty 8 inches in size!!
Colors:
Though I've hit on some of the colorations of Mollies, here's a compiled list;
White/Silver Black Orange/Gold Brown Green/Silvery Olive
Also, there are some nice mixes in color;
Black & White (Marble, Dalmation, Salt & Pepper)
Brown & Gold (Chocolate or chocolate chip)
Goldust (orange or yellow, with a dusting of black towards the back)
