When I first joined Iwaku, I wanted a fresh username. Something that completely separated me from reality. I chose an old Irish name originally, I cannot even recall what it meant, but I chose the turtle from the general avatar list.
I was told a few years back that there are two types of people in the world (though with varying degrees of cross over from person to person). Octopi: These are generally extroverted, touchy feely, got to do everything and be the life of the party, and never shut up kind of people. Turtles: These types of people are perfectly happy inside their shells, alone, without people trying to paw them or talk to them.
I understand that it's really impossible to categorize people into two nice neat little columns, but the latter is me. To a 'T'. I'm happiest alone, and I consider being in the same room as somebody, doing separate things, not touching, or talking, or looking at one another spending time together. At least about 90% of the time.
That being said, my best friend (the greatest and most beautiful lady ever
@Muna ) was calling me Beautiful Turtle, when I went to change my username, Beautiful Turtle didn't have quite the ring to it that I was looking for. So, I settled on Pretty Turtle.
I have other Turtle accounts now, as well, though they are mostly DammitTurtle.
Edit: Sorry, for the scattery-ness of my thoughts. It was hard to make it into a fluid story because there was a lot of different sources.