Lion's mane jellyfish

The Lion's Mane is the largest known species of jellyfish in the world. Its range is confined to cold, boreal waters of the Arctic, northern Atlantic and northern Pacific Oceans. They are seldom found farther south than 42°N latitude. Similar jellyfish (which may be the same species) are known from the seas off Australia and New Zealand.

Anatomy
Lion's Mane jellyfish-in spite of their name-are not fish, but invertebrates. They are relatives of sea anemones and corals. Jellies are 97 percent water. With no heart, no brain and no real eyes, jellyfish have three main parts: the round umbrella-like bodies or bells which propel the animals with a pumping or pulsating motion; tentacles that sting and immobilize prey using sting cells called nematocysts; and oral arms or flaps that are used to eat their prey. With this basic inventory, jellies manage to defend themselves from danger, make daily and seasonal journeys, stay together and occupy all the oceans of the world. Simple in design, fragile in build, jellies have few of the complex features many animals use to survive.

In the Arctic certain specimens can reach up to 8 feet in diameter, small or average ones ones may exceed 36 inches in diameter. With its tentacles fully stretched, the Arctic Lion's Mane Jellyfish is probably the longest animal on Earth--longer than a 100-foot blue whale! The bell of this jelly can be up to six feet across. The smallest Lion's Mane's measure only a quarter of an inch across.

Reproduction


The life cycle is the same as all Jellyfish. During reproduction, the male releases sperm through its mouth into the water column. The sperm swims into the mouth of the female where fertilization occurs. Early embryonic development begins either inside the female or in brood pouches along the oral arms. Small swimming larvae (planula) leave the mouth or brood pouches and enter the water column. The larvae then seek a shaded surface and attach to a hard surface, forming polyps. These polyps bud and create huge polyp colonies, divide individually and bud into infant jellyfish (Ephyra). In a few weeks, an ephyra will grow into a fully adult medusa, thus completing the complex life cycle. Jellyfish (on average) live three to six months.

Ecology
Most Lion's Mane Jellyfish are known to live only in radically temperate areas, such as Antarctica, the Arctic, and Australia. Most Jellyfish stay relatively close to the surface of the ocean, around 20 meters. Their diet includes planktonic crustaceans, such as copepods and cladocerans, fish eggs and larvae. It also contains large proportions of, ctenophores (comb jellies), hydromedusae, and scyphomedusae. The long tentacles snare such relatively large prey and bring them to the oral arms, where they are enveloped and digested. Predation effects have been studied in Australia, Norway, and Alaska, where populations of medusae remove only a small percentage of the zooplankton daily. Predators of the lion's mane jellyfish include seabirds, larger fish, other jellyfish species and sea turtles. A coldwater species, this jellyfish cannot cope with warmer waters. The jellyfish are pelagic for most of their lives but tend to settle in shallow, sheltered bays towards the end of their one-year lifespan. In the open ocean, lion's mane jellyfish act as floating oases for certain species, such as shrimp, medusafish, butterfish, harvestfish and juvenile prowfish, providing both a reliable source of food and protection from predators. 

Related References

 * Wikipedia Lion's Mane Jellyfish
 * PNW Jellyfish
 * Answers
 * Lion's Mane Jellyfish
 * Lion's Mane Jellyfish BBC
 * Facts Tennessee Aquarium