The largest invertebrate, Giant Squid lives only in deep water and its large size is due to phenomenon called deep sea gigantism. They have large eyes as big as the basketball, which helps them search their food in deep oceans. They have gills to breathe. Although it is believed that there are more than 500 species of them but very few are known. They have short life from 1 to 3 years and they generally die after spawning. Females are larger than males in size and they mate by injecting the sperms in ventral arms of the females. The sperm whale is their only natural enemy. The giant squids have three hearts, eight arms and tentacles. The largest squid is believed to be 60 feet long with a weight of 1000 kgs. They are carnivores and swim very fast. Many squids emit fluid to distract their enemies and some have bio-luminous organs and they shine in dark. They are highly intelligent, very active and adapt to changes easily.