Well, I guess the title says it all. I have read some folklore on mermaids but I haven't found any websites that can give me deep insight about the physical charactersitics (other than the fin) and the basic behavior/instincts. Any ideas? Thanks
wiki? There's going to be a finite amount you can find, given that they are mythical animals. You'd probably be better off reading what limited information you can find, and making the rest up yourself.
You may also wish to try this site Mermaid Lexicon. It has various info to look through, and though it is quite brief in regards to descriptions and behavioural characteristics of the different 'species', it has a gallery - which may help.
Ancient sailors' mermaid sightings are widely believed to have actually manatees. May not really be the physiacl appearance info you are looking for though. And just HOW long were those sailors at sea?