The phylum Cnidaria

Cnidaria

Aget 

                        Cnidaria is a group made up of more than 9,000 living species. Mostly marine animals, Cnidaria include the corals, hydras, jellyfish, Portuguese men-of-war, sea anemones, sea pens, sea whips, and sea fans. The word Cnidaria refers to Cnidocysts specialised cells which contain the Nematocysts, the stinging organelles that allow the Cnidaria to subdue their prey this is what makes the cnidarian phylum special. All cnidarians share these common characteristic:

-          Radially Symmetrical.

-          Eukaryotic and multicellular

-          Cnidarias have an internal sac for digestion which is called the gastrovascular cavity. The gastrovascular cavity has only one opening, a mouth, through which the animal takes in food and releases waste

-          Mostly carnivorous otherwise filter feeders. If carnivorous they use nematocysts to hunt prey.

-          Have specialized cells known as the nematocysts, a stinging organelle.

Their life cycle would start from an egg that has been fertilized by sperms. The fertilized egg would later on develop itself to a Planuta (larva stage) the planuta has cilia hairs surrounding its body to move around. Once the Planuta finds a perfect place to stay in like rocks they would turn into polyps. Polyps are U shaped and has a mouth with tentacles around it. Polyps can also form a colony where collected food will be shared among the colony members.

The polyp clones itself and grows, once it’s ready to bud it is known as a strobili. Then a clone of the polyp that has grown will bud off or fall off form the top of the polyp, this clone polyp is known as an Ephyra. Ephyras are like really-really tiny jelly-fish. The Ephyra would develop itself feeding by using its tentacles and nematocysts and grow into a fully matured Adult Medusa (adult jellyfish), medusa are bell-like shaped with tentacles and a gastrovascular cavity inside the “bell”. The adult medusa will eventually produce gametes and the cycle start all over again. But the medusa state is not available in the Anthozoa class, which only depend upto the Ephyra. The Ephyra of the Anthozoa would move to another place and settle and eventually produce a poly and the cycle starts all over again for the Anthozoa class.

The phylum Cnidaria is made up of four classes: Hydrozoa (hydrozoans); Scyphozoa (scyphozoans); Anthozoa (anthozoans); and Cubozoa (cubozoans).

Hydrozoa

Hydrozoans (hydroids) include the Portuguese man o’ war, freshwater hydra, and hydroids such as “snail fur,” which is commonly found on shells occupied by hermit crabs. In colonial forms, the polyps bud, but stay attached and share continuous body layers. However, individual members of the colony can perform different tasks, such as capturing prey, digestion and reproduction. Hydrozoans is a polypoid shape, U shaped with tentacles on top.

Example of this class:

Hydractinia echinata or also known as snail fur

(for image click here)

Scyphozoa

Scyphozoans are commonly known as “jellyfish” because the medusa is the dominant form in the life cycle. Most Scyphozoans are marine animals that live in shallow water. They have long tentacles that has lots of nematocysts on it which is used to stun preys.

Example of this class:

Chrysaora quinquecirrha or also known as the Atlantic sea nettle
(for image click here)

Anthozoa

Anthozoans (anemones and corals) are mostly all bottom dwelling animals, in a polypoid shape. This means that they live attached to the bottom with their tentacles and mouth pointing up.

Example of this class:

Urticina feline or also known as northern red anemone
(for image click here)

Cubozoans

Cubozoans looks like the scyphozoans at first however the umbrella of the Cubozoan medusa is a distinct cube shape and has four rubbery appendages to aid in swimming. So it is basically a scyphozoan that has a cube-shaped medusa instead of a more round bell-shape. The box jelly fish known as the “seas wasp” is known to be the most lethal jellyfish in the world, it’s found in the northern water of Australia.

Example of this class:

Chironex fleckeri or also known as sea wasp
(for image click here)

Bibiliography

Kennedy, J. (n.d.). Cnidaria - What Is Cnidaria. Retrieved January 24, 2015, from http://marinelife.about.com/od/glossary/g/cnidarian.htm

Programs and Classes. (n.d.). Retrieved January 24, 2015, from http://www.neaq.org/education_and_activities/teacher_resources/classroom_resources/teacher_guides/jellies_teacher_guide/jellies_information_sheets/what_is_a_jelly.php

The Phylum Cnidaria. (n.d.). Retrieved January 24, 2015, from http://www.earthlife.net/inverts/cnidaria.html

            

Share on Google Plus

About Unknown

This is a short description in the author block about the author. You edit it by entering text in the "Biographical Info" field in the user admin panel.