Thursday, March 1, 2007

Ineresting Facts

  • box jelly and irkujandi are the most dangerous creatures for human in the sea
  • the longest animal in the world is a cnidarian : The Jellyfish Praya can reach up to 120 feet
  • first animals with a definite body of definite form and shape
  • In Japan jellyfish are considered to be a delicacy
  • Jellyfish body is 95% Water
  • Jellyfish have been around for over 650 million years (they out date dinosaurs)
  • Some species of jellyfish contains a lot of protein and is thought to be able to play a large role in ending hunger and malnutrition in poor areas around the world
  • the Great Barrier Reef stretches over 1,300 miles along the Northern Eastern coast of Australia
  • Great Barrier Reef is made up of 2,600 different kinds of coral and supports up to 1,500 species of fish


Cnidaria: the phylum in which marine animals that are invertebrates with tentacles surrounding the mouth

polyp: sessile flower like cnidarian

medusa: motile bell shaped cnidarian

gastrovascular cavity: digestive cavity in cnidarians with only one opening

nematocyst: stinging structure on the tentacles of cnidarians that is used to paralyze or kill prey

hermaphrodite: individual that has both male and female reproductive organs

jellyfish:an invertebrate marine animal that, in its reproductive stage, has a nearly transparent gelatinous body shaped like an umbrella with trailing tentacles bearing stinging cells.

sea anemone:a solitary and often colorful sea animal with a squat cylindrical body that bears a ring of tentacles and is attached to rock or other nonliving material

coral:a marine organism that lives in colonies and has an external skeleton.

Take a look!

Orange Sea Pen

Red Polyps

Pink Sea Anemones

White Sea Anemones

Fried Egg Jelly Fish

Spotted Jellyfish

Green Sea Anemone
Moon Jellies


Cnidarians are motile at least one time in their life.

As you know, adult polyps do not move, they are sessile. But when they are young they are they are a larvae which swims a short distance to find a good environment to live in.

With its translucent parts, the jellyfish are nearly invisible in the water. Their bell-shaped top, flaps and dangling tentacles appear like the infamous Medusa, Greek mythological character with poisonous snakes instead of hair. One type of jellyfish moves through the water by attaching itself in the current to seaweed or other material, and catch prey at that spot. Others use jet propulsion by using specialized coronal muscles that are located on the bottom of the bell, and they force the water out of the bell to push the jellyfish forward. The ocean’s currents are the greatest determinant of the jellyfish’s movements, since even the ones that use jet propulsion cannot move against currents and waves. More significantly, without eyes or a brain, only nerve cells are directing the jellyfish to find food or avoid danger, with sensing organs identifying their location and distance from light. In order to balance in the water, sacs located on the bell rim stimulate nerves to contract muscles to keep the jellyfish stable.

So where do they live??

Cnidarians in general can be found all over the world, but most species live only in the sea.

Corals grow in shallow tropical waters around the world. For example, where a coral reef was formed, is the Great Barrier Reef off the coast of Australia.

Sea Anemones live in the sea from the low-tide line to great depths.

Some jellyfish can be found in the North Atlantic and Austrailia

Adaptations to Environment

Since Cnidarians live in aquatic environments, they need to be able to survive in water. To do this, they must have special body structures. For instance, to be able to move in the water, jellyfish have a special type of skeleton called a Hydrodtatic Skeleton. This type of skeleton is a skeleton where muscles surround a water-filled body cavity and the muscles are supported by this cavity. This type of skeleton allows Cnidarians to move quickly and easily through the water. As well, Cnidarians do not have teeth to bite into prey. Since they need to feed, Cnidarians use their nematocytes to stun, kill, or paralyze their prey. They may even use their tentacles to drag their prey into the "mouth" alive. Because cnidarians are living in the open sea with many predators, they need a form of protection. So, not only do nematocysts help feed the cnidarian, they help protect them as well. When a predator, like humans, touches the cnidarian's nerve net, the trigger cells are activated. This, in turn, signals the firing of a nematocyst. The nematocyst then injects a toxin into the predator. This toxin, in some cases, can be fatal. In other cases, like humans, getting "stung" by a cnidarian just results in a burn. As we can see, Cnidarians are more than fit to survive in their aquatic environment.

Relation to the Environment

Can you spot the fish?
1. Symbiotic relationships with other animals like certain fish, shrimp and other small animals. They live among the tentacles of large sea anemones, which protects and provides food for these symbionts. The symbionts in turn, help clean the sea anemone and protect it from certain predators.

2. Corals and reefs are important in the ecology of tropical oceans. In the tunnels, caves, and channels created, live beautiful and fascinating animals. Corals are important to humans too. They provide a home for food fishes and edible animals, as well as for organisms that produce shells, pearls, and other products. They have been used to build houses and to filter drinking water. Reefs are also there to protect the land from the waves. Large amoujnts of shoreline may be washed away without coral reefs. Fossil reefs give important clues to geologists about the locations of oil deposits.

3. Medical Research: Some snidarians like sponges produce chemicals to protect themselves from being infected, overgrown, or settled upon. These chemicals may provide us with drugs. Studies on how their poison operates reveal a lot about how the system works. For instance, sea wasp jellyfish which produces nerve poisons helped scientists better understand never-cell function.

Comparisons to Other Phyla

Cnidarians can be completely different from other invertebrates, but at the same time, they can be quite similar. Below are a few examples.


- Cnidaria and Platyhelminthes expel undigested material through the mouth

- Cnidaria and Planaria both lack specialized circulatory and respiratory systems

- Cnidaria and Platyhelminthes both lack a centralized nervous system


- Platyhelminthes have much more developed nervous systems compared to Cnidarians

- Cnidaria have nematocysts as protection. Other phyla have different methods (ie. Spicules in Porifera

- Nematoda have a complete gut, Cnidarians do not
Above is a picture of a sea anemone and on the right is the ventral side of a octopus. Can you see and similarities or differences?

Wednesday, February 28, 2007

Internal Transport

Cnidarians do not have any defined circulatory system that is to sat that there is no organized internal transport. Instead most cnidarians have a long gastrovascular cavities that help carry partially digested food throughout there body. The do not have any blood. Jellyfish have the gellatinous material throughout their body. This gel has been proven to be an oxygen storage for jellyfish. This amazing storage system was one of the main reasons jellyfish survived in the prehistoric ocean's where oxygen levels were drastically lower than what we know today.

Cnidarians use the free flowing water to respire and remove waste product by diffusion through their thin body walls.

Sunday, February 18, 2007

Feeding, Respiration, and Excretion in a Cnidarian


Cnidarians have tentacles that are around the mouth which help them to catch and eat food, they use their nematocysts to fire out barbs or toxins at the prey to kill, injure, or paralyze them. Almost all cnidarians are carnivores, and feed mainly on shrimps, amphipods, plankton, and any other small organism that gets trapped in the tentacles. Once the prey is entangled in the discharged nematocysts it is moved into the mouth and digested in its gastrovascular cavity.

As you can see in the photo this green sea anemone has been feeding. You can see it has some substance in its mouth in the centre.


Jellyfish like most Cnidarians breathe through gas exchange over their entire body surface. They do not have lungs or gills like most other marine species do. It would certainly be interesting if us humans could breath through our skin!


The cnidarians have a canallike cavity in their two-layered bodies for the ingestion, digestion, and egestion of food and wastes. Gaseous wastes are eliminated by diffusion, and solid wastes in dissolved or undissolved form pass out through an opening in the body wall that has 2 purposes of food intake and waste elimination.

Saturday, February 17, 2007

Cnidarian Reproduction

Moon Jelly ephyrae:
These are clones of the adult polp. They will grow to be either a male or female and look like the same bell shaped moon jellies.
Reproduction of a Polyp

Reproduction of a Polyp

Most polyps reproduce asexually by cloning themselves. The addition of new polyps makes a colony that stabilizes itself to the limestone skeletons of old polyps, producing the foundation of the reef. This type of reproduction is important because when cnidarians such as corals endure storm surges or hurricanes,they have the incredible ability to grow from broken-off pieces of the original colony. Polyps asexually reproduce by budding. Budding occurs when a part of the parent polyp goes off to form a new individual. Budding helps the polyp to copy itself several times and at the same time have the same tissue structures like the other polps. Later, the same polyp can produce sexually.

Reproduction of a Medusa

Reproduction of a Medusa

The medusae's reproduce sexually. The polyp by budding also makes a medusae, which either detach themselves and swim away or stay forever attached to the polyp. The medusae then produce new polyps by sexual reproduction. A medusa produces eggs or sperm, which are usually put into the water; when an egg is fertilized, it develops into a swimming larva, which eventually settles and grows into a polyp.

Cnidaria: Anatomy

Here is a diagram of the 2 different types of cnidaria, the medusa and the polyp

Functions of these Structures

Epidermis = The protective outer layer of the skin. In invertebrate animals, the epidermis is made up of a single layer of cells. In vertebrates, it is made up of many layers of cells and overlies the dermis. Hair and feathers grow from the epidermis

Mesoglea = it is the structure that helps the cnidarian receive all the water it needs.

Gastrodermis/Gastrovascular Cavity = this structure is used to help in digestion and transport of nutrients to the rest of the body.

Nematocysts = the structure that detects if prey is near and releases a barb or toxin to the prey either killing, wound, or paralyzing the prey.

Tentacle = the structure used for feeding, grasping, feeling

Digestive Cavity = the structure used for digestion by diffusion