You're right. Dolphins or porpoises they are. https://blogs.oracle.com/chandan/entry/some_one_asked_me_how
"Changing a backdrop isn't that intuitive, right click menu does not have a "Change Background.." option, so most users are stuck with dancing dolphins or some low color background on CDE. Some don't even know that they can change the backdrop.
There's a screenshot of Solaris with CDE. The backdrop has been changed from a dolphin to a rhino.
