Jellyfish

Don't get stung!

Jellyfish, a marine invertebrate belonging in the Scyphozoans can be found in every part of every ocean and even sometimes in fresh water.  Some jellyfish's sting can be deadly, such as the sea nettle.  Other species of jellyfish can be completely harmless to humans!  Jellyfish look like gooey, sticky blobs, when they are washed up on the beach.  The jellyfish are graceful in the water.  Jellyfish are usually 1 inch to 200 feet long!  Jellyfish are invertebrates and not fish at all.  "They have no head, no brains, heart, or eyes. There are jellies in every part of the ocean every where you go.  There are jellyfish in Antarctica to the Gulf of Mexico!  Jellyfish are all around us.

"Jellyfish have tendrils or arms with thousands of microscopic nematocysts."  Every nematocyst has a "trigger" and a capsule containing a stinging filament armed with barbs.  When a jellyfish touches an object, the filament rapidly unwinds. The jellyfish strikes at his prey, and injects toxins.  Then it can pull its prey into his mouth. Using a nervous system called a "nerve net" a jellyfish detects other animals.  "Touch stimuli are conducted by nerve rings, through the rhopalial lappet", located around the jellyfish's, through the nerve cells.  Light-sensitive organs that do not form images but are used to figure out down from up, responding to sunlight glistening on the surface of the sea. There is no digestive system, central nervous system, osmoregulatory system, circulatory, or respiratory system located in the jellyfish. They use the gastrodermal rim of the gastrovascular system, where nutrient are absorbed, to digest there food.  There skin is thin enough that the body is oxygenated by diffusion, so they don't need a respiratory system.  Jelly fish free-float most of the time since they have no control over their movement.  The jellyfish can sometimes move vertically using their hydrostatic skeleton. "The outer side of a jellyfish is lined with a jelly-like material called an ectoplasm (ecto=outer and plasma=cytoplasm). Jellyfish can form swarms or "blooms" consisting of hundred to thousands of jellyfish.  To form these blooms, a jellyfish goes through a complex process.  This process depends on ocean currents, temperature, nutrients, and also ambient oxygen concentrations.  These creatures some of the time mass breed during the time of these blooms. These breeding times lead to rapid population expansion.  Some people are concerned about these mass breeding.  Jellyfish population is expanding rapidly and invading our oceans! According to Claudia Mills of the University of Washington people's impact on marine systems is affecting jellyfish blooms.  Marsh Youngbluth, a jellyfish researcher says, "Jellyfish feed on the same kinds of prey as adult and young fishes, so if fish are removed from equation, jellyfish are likely to move in." The Gulf of Mexico has been highly impacted by jellyfish blooms.  There are many other places that have been seriously impacted by jellyfish. Jellyfish go through many stages in their life, the first being the polypoid stage.  A jellyfish forms into sessile stalk, a sessile stalk catches passing food or another figure which free-floats.  The bottom of the jellyfish (where the tentacles are) faces upwards. The medusa stage is the second stage in the life process.  At this stage the jellyfish has an umbrella-shaped body.  This body shape is called a bell.  "The medusa's tentacles are fringe-like protrusions from the border of the bell." Jellyfish are male or female.  In reproduction, the male's sperm is released in the water.  The female lets the sperm swim into her mouth, beginning the fertilization of the ova.  The moon jellyfish use a totally different process.  The eggs link onto pits in the oral arms.   After these processes, the jellyfish larva form.  Theses larva are called planula.  It finds are firm surface to settle on and forms into a polyp.  These creatures are tiny and cup-shaped with tentacles surrounding it.  A polyp closely resembles a sea anemone.  Then, the polyp starts to reproduce asexually.  Many jellyfish species are able to reproduce right from the medusa stage.