Memphis the Mermaid is originally from GaiaOnline, you buy her and put her in your GaiaOnline Aquarium. I've been obsessing over her for the longest time because I've always wanted a mermaid as a pet.
Here's a screen shot I took of Memphis the Mermaid from GaiaOnline.
Here's a moving from I got from I can't remember where, online:
Here's an ugly Gaia cosplay of it that I did:
Oh and here's a chibi version I took from the SDPlus #322 Memphis: