Phylum: Coelenterata - NEET PDF Download

PLYLUM-COELENTERATA

Phylum: Coelenterata

• Leuckart coined name Coelenterate. 

 –  Hatschek named Cnidaria on the basis of stinging cells. Peyssonal & Trembley established animal nature of Coelenterata.

–    Cnidology-Study of cindaria

–    Mostly marine, few fresh-water (Hydra.) Carnivorous, some are fixed or free floating.

–    Coelenterates have two types of forms (Dimorphic)

(1) Polyp

(2) Medusa

- Cylindrical in shape

- Mostly sessile, but some are motile

- May be solitary or Colonial

- Types of structures : -

• Gastrozooids (Hydranth) - For Nutrition
• Dactylozooids - For Protection
• Gonozooids - For Reproduction     

- Umbrella-like

- Free swimming

- Always solitary

- Types of structures : -

• Phyllozooids - For Protection
• Nectophore - For swimming
• Gonophore - For Reproduction
• Pneumatophores - For Swimming

Either or both zooids may occur in a species.

If both forms are found in a group it is called Cormidia.

If both are found in a species, two form alternate in life cycle. (Alternation of generation or Metagenesis)

–    Group of different types of zooids in polyp or medusa shows polymorphism.

–    Coelenterates are usually having radial symmetry, Some Anthozoans have Biradial symmetry.                 

–    Coelenterates have two Germ layers (1) Ectoderm (2) Endoderm i.e. They are Diploblastic

–    Coelenterates have Tissue level of organisation.

–    No head and appendages. The oral end (mouth) often bears slender, flexible process hollow tentacles.

–    Body wall consists of -           

(a)  Epidermis (Outer layer) - Formed of 7 different types of cells.

Stinging cells or Nematoblast or Cnidoblast (for offence & defence) characteristic of coelenterata.  Inject Hypnotoxin.     

Cnidoblasts : A – Undischarged ; B – Discharged discovered and regeneratin in Hydra.

–    Interstitial cells (Totipotent and act as reserve to replace worn out cells/germ cells/Nematocyst) ;
Epithelio - muscular cells ; Glandulo – muscular cells ; Sensory cells ;  Germ cells  

(b)  Gastrodermis (Inner layer) - Formed of 5-different types of cells such as    

–    Endothelia - muscular cells or Nutritive cells (with food vacuole) ;  Interstitial cells ; Sensory cells ; Nerve cells ; Germ cells     

Between these two layers, gelatinous Mesogloea is present which contain free cells. Mesogloea is secreted by both the above layers.

–    Body of coelenterates may be supported by horny or calcareous exoskeleton.

–    Cavity of the Coelenteron is having single aperture. Mouth serve both purpose i.e. incomplete digestion tract (Blind sac).

Digestion is Extra-cellular as well as Intracellular i.e. takes place in Coelenteron as well as food vacuole. Coelenteron is also responsible for distribution of food besides partly digesting it. This dual role named coelenteron as Gastrovascular cavity.

–  Respiration and Excretion takes place by diffusion of gases through body surface.

Excretory matter is Ammonia.

–  Nervous system present both in polyp & medusa and form a loose net work of nerve fibres on either side of mesogloea (Diffused type). Neurons are non-polar. Sensory cell are also present. Medusa have sense organ Rhopalia or statocyst/Tentaculocyst.

– Sexes may be separate or united. Coelenterates can reproduce Asexually by Budding (Polyp) and by sexually-(Medusa).

Gonads have no duct. Fertilization may be External or internal.

Cleavage is Holoblastic.               

Development includes larva.

Larva of Obelia – Planula  (free living) and scyphistoma larva fixed polyp like.

Larva of Aurelia – Ephyra , Scyphistoma

Coelenterata is classified into three classes

Anthozoa (Actinozoa)

–   Exclusively marine

–   Only polyp form

–   No manubrium

–   Velum absent.

–   Mesogloea contains cells & fibres

–   Gastro vascular cavity have compartment  i.e. mesenteries

.–    Gonads -Endoermal and shed gametes into the digestive tract escape via mouth

–   Cnidoblast is present in epidermis & Gastrodermis

e.g. This class has two types of animal

(1)  Anemones - Skeleton absent

*Adamsia - sea anemone

Metridium - Sea anemone

(2) Coral - CaCO₃ Skeleton

Astraea - the star coral

Pennatula - the sea pen

Gorgonia - the sea fan

Pteroides - Sea feather

Renilla - Sea pansy

Tubipora - Organ - pipe coral

Alcyonium - Dead man's finger (Soft coral)

Corallium - Red coral (Moonga)

Meandrina - Brain coral

Madrepora - Stag-Horn coral

Fungia - Mushroom coral

Scyphozoa

–     Exclusively marine

–     Medusa form is more common

–     Polyp form reduced or absent and  have small manubrium

–     Velum absent. [Acraspedote]

–     Mesogloea is thick, gelatinous and contains cells.

–     Gastrovascular cavity undivided.

–     Gonads are Endodermal and shed the gametes into the digestive tract when escape through  the mouth.

–     Cnidoblast is present in epidermis & Gastrodermis

e.g*Aurelia - the Jelly fish, Moon jally,Larva - Ephyra

Rhizostoma - Many mouth (Polystomum)

Cyanea - Sun Jelly

Hydrozoa

–   Fresh water as well as marine  

–   Polyp & medusa often show polymorphism & metagenesis.

–   Polyps with manubrium

–   Medusa have a velum (Craspedote)

–   Mesogloea is Acellular

–   Gastrovascular cavity undivided.

– Gonads are Ectodermal and shed gametes directly in to the surrounding water.

–   Cnidoblast is present only in epidermis

  e.g.-Hydra - Fresh water polyp

Obelia - the sea fur, (Polyp, Blastostyles,  Medusa shows metagenesis)

Physalia- the Portuguese man-of-war. (Neurotoxic, gas  gland present)

Bougainvillea

Vellela - Little sail

Millipora (Sting coral)  

PHYLUM – CTENOPHORA :

– Ctenophora name was given by Eschescboltz. Commonly called ‘‘Sea-gooseberries’’ or ‘‘Comb-jellies’’ or ‘‘Sea-walnuts’’. 

–    Nematoblasts are absent, so they are also called ‘‘acnidaria’’

–    Exclusively marine and pelagic (float on sea surface) and show Bioluminescence.

• Body form may be spherical, cylindrical or Pear-shaped. 

–    Body is soft transparent jelly like having

Biradial symmetry with tissue grade body organization.

–    Triploblastic  Mesoglea contains amoeboid mesodermal cells called Colloblast, Amoeboid cells and smooth muscle cell.

–    Locomotion takes place by the presence of 8 ciliary comb plates on the body surface.

–    Special sensory structure statocyst at the opposite end (absoral end) of the mouth is present.

• Tentacles may be present or absent. When present, the number of tentacles are two. They are solid and possess adhesive cells called as colloblasts (lasso cells).

–    Digestion is both extracellular and intracellular. These are carnivorous animals

–    The animals move by cilia, which join together to form comb plates, there are eight median comb plates forming locomotory organs.

– Resp. system, skeletal, circulatory & excretory system are absent.Nervous system is diffuse type.

– All animals are Bisexual. Complex type of sexual reproduction is found. Metagenesis is absent.

Gonads = endodermal, Fertilization is external.

< >Regeneration is normally found.  

< >Development is of indirect type. Life cycle involves a free living Cydippid larval stage.  

–    Asexual reproduction is absent.

< >Regeneration & paedogenesis is normally found.

e.g. *Pleurobrachia   

Beroe - Swimming eye of cat.

Velamen

Cestum –       ‘‘Venus's girdle’’

*Ctenoplana – Commensal with Alcyonium.

Hormiphora

Euchlora rubra – with cnidoblast (Exception)