The largest jellyfish is the lion’s mane jellyfish (Cyanea capillata) which can reach the dimensions of 4 meters across.
The Lion’s Mane Jellyfish is native to Japan, but it has spread widely through the Indo-Pacific region and dominates coastal waters along Australia. It can be found in great numbers off Tasmania but also often drifts near to Western Australian shores. This species lives for approximately 3 years before dying, with its size gradually decreasing during this time until only a section 5 cm wide remains by year 3. Females are slightly larger than males, typically measuring about 2x2m while males are 1x1m, that size difference resulting from female post-reproductive reproductive activity together with female metabolic processes. The results of this reproductive activity is an egg mass which can contain anywhere from 5,000 to 40 million eggs.
While the size of these creatures varies depending on age and sex, their tentacles do not. These tentacles grow up to 36m long and are covered with thousands upon thousands of stinging cells known as nematocysts, each capable of delivering venom powerful enough to kill small fish. This jellyfish hunts any smaller prey that comes within range – its diet consisting primarily of small fish, crustaceans and other zooplanktonic organisms that become trapped in the trailing tentacles. It has also been reported to consume turtles and birds by swimming around them “much like a tiger” before ensnaring them with its tentacles and pulling them in.
Although the venom of this creature is believed to be the most poisonous in the world, it remains harmless unless ingested because it is contained within tiny capsules called nematocysts. These nematocysts are barbed stingers that attach themselves to passing fish using a thread-like attachment that only releases once they penetrate tissue layers deep enough. Ingesting these creatures can result in searing pain followed by severe nausea, but fatalities resulting from jellyfish stings are considered extremely rare.