Another good Marine ID site

[bottlefish]

It's got much the same look and feel as fishbase.org, however this site covers all marine life:

http://www.sealifebase.org

It's a little trickier to use, you really need to have an idea of what you are looking for before you start looking (especially if you're trying to name a crustacean), and not all the species have pics, but still, helped me name a couple of tricky ones!