Deep Sea Jelly Fishes

Common Name: Jelly Fish
Scientific Name: Aurelia aurita (Common jellyfish)


fish are members of the phylum Cnidaria, a structurally simple marine group of both fixed and mobile animals: sea anemones, sea whips, corals and hydroids are polyps that grow attached to rocks or other hard surfaces; jellyfish and colonial siphonophores like the Portuguese man-of-war are mobile (either actively swimming or subject to winds and currents).

Nature of Jellyfish

Instead of a brain, jellyfish possess an elementary nervous system, or nerve net, which consists of receptors capable of detecting light, odor and other stimuli and coordinating appropriate responses.

Jellyfish are composed of an outer layer (epidermis), which covers the external body surface, and an inner layer (gastrodermis), which lines the gut. Between the epidermis and gastrodermis is a layer of thick elastic jellylike substance called mesoglea ("middle jelly"). Jellyfish have a simple digestive cavity, (coelenteron), which acts as a gullet, stomach and intestine, with one opening for both the mouth and anus. Four to eight oral arms are located near the mouth and are used to transport food that has been captured by the tentacles to the mouth.


Jellyfish inhabit every major oceanic area of the world and are capable of withstanding a wide range of temperatures and salinities. Most live in shallow coastal waters, but a few inhabit depths of 12,000 feet!


Jellyfish are carnivorous, feeding mostly on a variety of zooplankton, comb jellies and occasionally other jellyfish. Larger species, however, are capable of capturing and devouring large crustaceans and other marine organisms.Some species, including the mushroom and cannonball jellyfish, are even considered a delicacy by humans. Pickled or semi-dried mushroom jellyfish are consumed in large quantities in Asia, where they constitute a multimillion-dollar part of the seafood business.

Types of Jellyfish

  • Cannonball Jelly(Stomolophus meleagris)
  • Mushroom Jelly(Rhopilema verrilli)
  • Southern Moon Jelly(Aurelia marginalis)
  • Lion's Mane(Cyanea capillata)
  • Sea Nettle(Chrysaora quinquecirrha)


The adult jellyfish drifts in the water with limited control over its horizontal movement. It is, however, endowed with muscles that allow it to contract its bell, reducing the space under it and forcing water out through the opening. This pulsating rhythm allows for regulation of vertical movement. Because jellyfish are sensitive to light, this vertical movement can be important. Some jellyfish, like the sea wasp, descend to deeper waters during the bright sun of the midday and surface during early morning, late afternoon and evening.

Special Features or Habits

Jellyfish are equipped with a specialized venom apparatus (cnidoblast) for defense and feeding. A capsule (nematocyst) inside the cnidoblast contains a trigger and a stinging structure. The stinging structure varies according to species but generally consists of a hollow coiled thread with barbs lining its length. Nematocysts are concentrated on the tentacles or oral arms.Nematocysts are activated when tentacles make contact with an object.

Stings usually paralyze or kill only small creatures (fish, small crustaceans), but some jellyfish are harmful to humans. Although jellyfish do not "attack" humans, swimmers and beachcombers can be stung when they come into contact with the jellyfish tentacles with functional nematocysts.

Treatment of Sting

Primary first aid for any jellyfish sting should be to minimize the number of nematocysts discharging into the skin and to reduce the harmful effects of the venom.A variety of substances have been used to reduce the effects of jellyfish stings. Meat tenderizer, sugar, vinegar, plant juices and sodium bicarbonate have all been used with varying degrees of success.


Care should be taken when swimming in areas where dangerous jellies are known to exist or when an abundance of jellies of any type is present. Keep in mind that tentacles of some species may trail a great distance from the body of the organism and should be given lots of room.Rubber skin-diving suits offer protection against most contact.