Jellyfish – The Deadly Brainless Water Creatures

Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the Scyphozoa (about 200 species), Staurozoa (about 50 species), Cubozoa (about 20 species), and Hydrozoa (about 1000-1500 species that make jellyfish and many more that do not). The jellyfish in these groups are also called, respectively, scyphomedusae, stauromedusae, cubomedusae, and hydromedusae; "medusa" (plural "medusae") is another word for jellyfish. Jellyfish are found in every ocean, from the surface to the deep sea. Some hydrozoan jellyfish, or hydromedusae, are also found in fresh water.


Jellyfish don't have specialized digestive, osmoregulatory, central nervous, respiratory, or circulatory systems. They digest using the gastrodermal lining of the gastrovascular cavity, where nutrients are absorbed. They do not need a respiratory system since their skin is thin enough that the body is oxygenated by diffusion. They have limited control over movement, but can use their hydrostatic skeleton accomplish movement through contraction-pulsations of the bell-like body; some species actively swim most of the time, while others are passive much of the time. Jellyfish are composed of more than 90% water; most of their umbrella mass is a gelatinous material - the jelly - called mesoglea which is surrounded by two layers of epithelial cells which form the exumbrella (top surface) and subumbrella (bottom surface) of the bell, or body.


Jellyfish do not have a brain or central nervous system, but rather have a loose network of nerves, located in the epidermis, which is called a "nerve net". A jellyfish detects various stimuli including the touch of other animals via this nerve net, which then transmits impulses both throughout the nerve net and around a circular nerve ring, through the rhopalial lappet, located at the rim of the jellyfish body, to other nerve cells. Some jellyfish also have ocelli: light-sensitive organs that do not form images but which can detect light, and are used to determine up from down, responding to sunlight shining on the water's surface.


As I've said, Jellyfish has no bones, brains, head, heart, eyes, nor ears. But what a sting! The sting of some "jellies," can be deadly while others are harmless to humans. Jellyfish are not fish at all. They are invertebrates, relatives of corals and sea anemones.


Don't get stung!

A jellyfish fires its poison whenever its tentacles brush against an object. In humans, the poison usually causes a sharp, burning sensation that may last from minutes to hours.


1. Take note of jellyfish warning signs posted on the beach.

2. Be careful around jellies washed up on the sand. Some still sting if their tentacles are wet. Tentacles torn off a jelly can sting, too.

3. If you are stung, wash the wound with vinegar or rubbing alcohol. Or sprinkle meat tenderizer or put a baking soda and water paste on the sting. Don't rinse with water, which could release more poison.

4. Lifeguards usually give first aid for stings. See a doctor if you have an allergic reaction.


All jellies sting, but not all jellies have poison that hurts humans. Of the 2,000 species of jellyfish, only about 70 seriously harm or occasionally kill people. Listed below are the more dangerous jellies and where you can find—and avoid—them.


Lion's mane

Atlantic Ocean from above the Arctic Circle to Florida; Gulf of Mexico; Pacific Ocean from Alaska to southern California


Portuguese man-of-war

Gulf of Mexico; Caribbean Sea near the Bahamas; West Indies


Sea nettle

Chesapeake Bay; Pacific Ocean from Alaska to southern California; Atlantic Ocean from Massachusetts to Florida; Gulf of Mexico


Sea wasp

Pacific Ocean near northern Australia, Philippines


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Source: Wikipedia & Nationalgeographic

Axolotl – The Water Monster

The axolotl (Ambystoma mexicanum) is the best-known of the Mexican neotenic mole salamanders belonging to the Tiger Salamander complex. Larvae of this species fail to undergo metamorphosis, so the adults remain aquatic and gilled. The species originates from the lake underlying Mexico City and are also called ajolote (which is also the common name for Mexican Mole Lizards).


Axolotls are used extensively in scientific research due to their ability to regenerate most body parts, ease of breeding, and large embryos. They are commonly kept as pets in the United States, Great Britain (under the spelling axlotl), Australia, Japan and other countries.

Axolotls should not be confused with waterdogs, the larval stage of the closely related Tiger Salamanders (Ambystoma tigrinum and Ambystoma mavortium), which is widespread in much of North America which also occasionally become neotenic, nor with mudpuppies (Necturus spp.), fully-aquatic salamanders which are unrelated to the axolotl but which bear a superficial resemblance.

As of 2008, axolotls are near extinction, due to urbanization in Mexico City, and polluted waters. Nonnative fish have also recently been introduced to the waters. These new fish have been eating the axolotls' babies, as well as its primary source of food. The axolotl is currently on the International Union for Conservation of Nature's annual Red List of threatened species.

Description:

A sexually-mature adult axolotl, at age 18-24 months, ranges in length from 15–45 centimetres (5.9–18 in), although a size close to 23 centimetres (9.1 in) is most common and greater than 30 centimetres (12 in) is rare. Axolotls possess features typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent.


Their heads are wide, and their eyes are lidless. Their limbs are underdeveloped and possess long, thin digits. Males are identified by their swollen cloacae lined with papillae, while females are noticeable for their wider bodies full of eggs. Three pairs of external gill stalks (rami) originate behind their heads and are used to move oxygenated water.


The external gill rami are lined with filaments (fimbriae) to increase surface area for gas exchange. Four gill slits lined with gill rakers are hidden underneath the external gills. Axolotls have barely visible vestigial teeth which would have developed during metamorphosis. The primary method of feeding is by suction, during which their rakers interlock to close the gill slits. External gills are used for respiration, although buccal pumping (gulping air from the surface) may also be used in order to provide oxygen to their lungs.


Axolotls have four different colours, two naturally occurring colours and two mutants. The two naturally occurring colours are wildtype (Varying shades of brown usually with spots) and melanoid (black). The two mutant colours are leucistic (pale pink with black eyes) and albino (golden, tan or pale pink with pink eyes).via

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Video of Axolotl.

Stingray – The Deadly Water Creature

Stingrays are commonly found in the shallow coastal waters of temperate seas. They spend the majority of their time inactive, partially buried in sand, often moving only with the sway of the tide. The stingray's coloration commonly reflects the seafloor's shading, camouflaging it from predatory sharks and larger rays. Their flattened bodies are composed of pectoral fins joined to their head and trunk with an infamous tail trailing behind.


While the stingray's eyes peer out from its dorsal side, its mouth, nostrils, and gill slits are situated on its underbelly. Its eyes are therefore not thought by scientists to play a considerable role in hunting. Like its shark relatives, the stingray is outfitted with electrical sensors called ampullae of Lorenzini. Located around the stingray's mouth, these organs sense the natural electrical charges of potential prey. Many rays have jaw teeth to enable them to crush mollusks such as clams, oysters, and mussels.


When they are inclined to move, most stingrays swim by undulating their bodies like a wave; others flap their sides like wings. The tail may also be used to maneuver in the water, but its primary purpose is protection.


The stingray's spine, or barb, can be ominously fashioned with serrated edges and a sharp point. The underside may produce venom, which can be fatal to humans, and which can remain deadly even after the stingray's death. In Greek mythology, Odysseus, the great king of Ithaca, was killed when his son, Telegonus, struck him using a spear tipped with the spine of a stingray.via


Other picture of stingray.

Antarctic Octopus (Paraledone Turqueti)

This animal is quite small and is usually an inhabitant of deeper water. Its thin arms are used for capturing less robust prey, like small shrimps and other crustaceans.

Pareledone turqueti, also known as Turquet's Octopus, this creature lives in the icy depths around Antarctica, particularly the South Shetland Islands and South Georgia. It can live in shallow waters or go as deep as 13,000ft (4000m)...the temperatures of these waters range from 28 to 50°F (−2 to 10°C) Its body length is about 5 inches (15cm) and the legs extend to roughly the same.


Almost nothing is known about this species including diet but it is assumed to feed on crustaceans such as shrimp, krill and crabs like its cousins. It is part of an ecosystem that is experiencing some turmoil due to the recent breakup of ice in the polar regions. We can expect quite a few new species to be discovered in this untouched part of the world.


Other Pictures of Antarctic Octopus.

About Underwater Creatures

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Underwater Creatures is a site that offers inforamtion about marine animals.