Authenticated (17/11/07) by William F. Perrin, Senior Scientist for Marine Mammals, National Marine Fisheries Service, Southwest Fisheries Science Centre.
http://swfsc.noaa.gov
Dorsal fin: The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
Invertebrates: Animals with no backbone.
Melon: A lump of fatty tissue that forms the bulging forehead of toothed cetaceans (whales, dolphins and porpoises) thought to focus sound during echolocation.