parasitic louse (crustacean family) that attacks fish. Enters fish through gills, then attaches itself to base of tongue. Louse restricts blood flow to tongue, feeding off it, causing the tongue to wither and die where it then takes its place. Then it lives in the fishes mouth, working as a fully functioning tongue and living off its blood and saliva. Apparently this does not harm the fish and is the only known case of a parasite replacing a whole organ.
mudskippers - fish that have evolved to live out of water. These fish are completely amphibious, and use their pectoral fins to walk around on land. They have a large gill chamber that retains water and closes tightly when they are not immersed in water.
Salpa Maggiore, New Zealand: This tunicate moves by pumping water through its body and has a complex life cycle living both solitary and as a chain of salps which swim and feed together. Picture: Conaugh Fraser / Caters http://en.wikipedia.org/wiki/Salp #Salp