Phylum Cnidaria Prepared by : Nada H. Lubbad - PowerPoint Presentation

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Phylum Cnidaria

Prepared by : Nada H. Lubbad

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General Characteristic :

Metazoa ( true tissues ).Coelentrata , single cavity to the body ( enteron or gastrovascular cavity ) Radially symmetrical.Diploblastic:

- Ectoderm ( dermis )

- Endoderm ( Gasrodermis )

- Mesoglea ( non- living jelly - like structure )

Possess a single opening that serve as

a mouth

and

anus

which surrounded by

tentacles.

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Life form:

Mostly marine.Few in fresh water.Solitary , colonial , sedentary , free- swimming.

Feeding:

Carnivores.Cnidarians use tentacles to capture prey and push them into their mouths.The mouth leads to gastrovascular cavity which function in digestion.

Tentacles :

It used for

capture of prey

and

defense

.

Cnidocytes

, specialized cells found on the surface of structure.

Trigger

, section found on the top of each Cnidocytes. When this area of cell is touched , a coiled thread is discharged. This causing the prey or predator to become unable to fight or escape.

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Polymorphism:

Many Coelentrata exist in two body form – a polyp and medusa.

Polyp

Medusa

Tubular body

Umbrella-shaped body

Mouth directed upward

Mouth directed downward

Small amount of mesoglea

Large amount of mesoglea

sessile

Motile – float

freely in the water

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Phylum Cnidaria is divided into 4 classes:

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Class hydrozoa

Hydra

General features:

Inhabitant of fresh water.Medusoid stage is absent.The hydroid stage is solitary and sedentary.Hydra is about 4-10 mm in length.It feeding on small crustaceans such as Daphina and other small animals.Symbiotic zoochlorellae live in the endodermal cells of H. viridis giving the animal its green coloration.

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Reproduction:

Asexual reproduction:

by budding , the buds are usually connected to the body of the parent at the connection of its two lower thirds.

2. Sexual reproduction:

Gonads, organs of sexual reproduction.

Testes

: appear as a conical swellings near the oral cone.

Ovaries

: they are formed about the middle of the body.

Hydra is either :

- Hermaphrodite (monoecious), developing both types of gonad in the same individual.

- unisexual (dioecious), the sexes are separate.

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Obelia

Marine coelenterate.Dimorphic, exhibiting two different forms in life cycle ( Hydroid and Medusoid). - Hydroid form : colonial, sedentary . It reproduces asexually giving the Medusoid form. - Medusoid form: free- swimming. It reproduces sexually giving rise to hydroid form again.

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Feeding polyp

( Gastrozooid )

Reproductive polyp

( Gonozooid )

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Free- swimming larvae ( Planula )

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Class scyphozoan (scyphomedusae) cup animal

It includes the larger jellyfishes.Marine.The medusa is the predominant phase , the hydroid stage is reduced and included in the life – history only as a polypoid larva.

Aurelia

The sexes are separate.

Scyphistoma

: polyp form , stores food , multiplies asexually and produces a number of discs called

ephyra

by a

strobilization

process.

Ephyra

: a small larva medusa.

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Class cubozoa ( cubomedusae )

They are known as box jellyfish, because in transverse section the bells appear to be square.They are effective predators and strong swimmers.Their nematocysts are especially potent, sometimes resulting in the death of human swimmers.

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Class Anthozoa ( Actinozoa )Flower animalsSea Anemones & corals

It includes the sea anemones and reef-building corals.Entirely marine.Solitary or colonial .It exists only in the hydroid stage.It has an oral disc bearing hollow tentacles.The enteron is divided by mesenteries, and the entrance to the enteron is by a stomodaeum.The Anthozoa are divided into two subclasses: Octocorallia ( Alcyonaria) and Hexacorallia (zoantharia).

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