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