The Black Sea Nettle. These large jellyfish can grow to be over three feet in diameter, and their tentacles can be over 25 feet long. Despite their large size, much about them is still unknown, and they are relatively new to science: black sea nettles weren't an official species until 1997! This is because they are rarely observed in the wild, preferring calm deep water, and are difficult to raise in containment. http://ocean.si.edu/ocean-photos/black-sea-nettle
lso known as the “alarm jelly” or Coronate medusa, the Atolla jellyfish lives in the bathypelagic zone of the ocean, between depths of 1,000 – 4,000 meters. This region is known as the “midnight zone,” because no sunlight penetrates these depths. This factor has not stifled life, however, as the species that inhabit this region have adapted special functions and behaviors help them conserve energy and find food and protect themselves from other predators lurking in the dark as well.