Transcript a mouth

Phylum Cnidaria
Prepared by : Nada H. Lubbad
 General Characteristic :
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Metazoa ( true tissues ).
Coelentrata , single cavity to the body ( enteron or gastrovascular cavity )
Radially symmetrical.
Diploblastic: - Ectoderm ( dermis )
- Mesoglea ( non- living jelly - like structure )
- Endoderm ( Gasrodermis )
o Possess a single opening that serve as a mouth
and anus which surrounded by tentacles.
 Life form:
o Mostly marine.
o Few in fresh water.
o Solitary , colonial , sedentary , free- swimming.
 Feeding:
o Carnivores.
o Cnidarians use tentacles to capture prey and push them into their mouths.
o 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.
 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
Phylum Cnidaria is divided into 4 classes:
Class hydrozoa
Hydra
General features:
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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.
Reproduction:
1. 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.
Obelia
o Marine coelenterate.
o 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.
Reproductive polyp
( Gonozooid )
Feeding polyp
( Gastrozooid )
Free- swimming larvae ( Planula )
Class scyphozoan (scyphomedusae)
cup animal
o It includes the larger jellyfishes.
o Marine.
o The medusa is the predominant phase , the hydroid stage is
reduced and included in the life – history only as a polypoid
larva.
 Aurelia
o The sexes are separate.
o Scyphistoma : polyp form , stores food , multiplies asexually and produces a
number of discs called ephyra by a strobilization process.
o Ephyra : a small larva medusa.
Class cubozoa ( cubomedusae )
o They are known as box jellyfish, because in transverse section
the bells appear to be square.
o They are effective predators and strong swimmers.
o Their nematocysts are especially potent, sometimes resulting
in the death of human swimmers.
Class Anthozoa ( Actinozoa )
Flower animals
Sea Anemones & corals
o It includes the sea anemones and reef-building corals.
o Entirely marine.
o Solitary or colonial .
o It exists only in the hydroid stage.
o It has an oral disc bearing hollow tentacles.
o The enteron is divided by mesenteries, and the entrance to the enteron is by a
stomodaeum.
o The Anthozoa are divided into two subclasses: Octocorallia ( Alcyonaria) and
Hexacorallia (zoantharia).