the mantis gets my vote ,these little bugs from another world are amazing. its the only thing in my sw tank and thats enough. not to many things you can say that about.aggressive and colorful just plain weird.
Ive had a 6 inch red peacock mantis destroy baseball sized hermits.. : ) the mantis was relentless, went up inside the shell to beat away at his claws..
not sure but my lfs has some that look exactly like the right in the second pic.strangley to me (freshwater guy) when i turned on the lights in our 6gal salt tank (my nephews) i noticed what looked exactly like a mantis shrimp just about an 1/8th inch long and a few other bugs but then everything scattered
blue ring octo is my fav..... but mantis shrimps are awesome.... there are lots of crazy salt inverts.... think of how many havent even been discovered yet...