Phylum porifera - structure , classification , characteristics and reproduction pdf downdoad

                                                                PORIFERA        

                                                              Phylum porifera

 

                                  Study of porifera called --------Parazooology.      

                                  Term porifera given --------------  Grant .   

                        *  Phylum Porifera are the lowest multicellular animals belonging to the kingdom Animalia.   

                        *          The word “Porifera” mainly refers to the pore bearers or pore bearing species    

                     * This phylum includes about 5000 species. Poriferans are pore-bearing first multicellular animals. The pores are known as Ostia        

Characteristics of Phylum Porifera

Some of the important characteristics of phylum Porifera are mentioned below.

1. The cells of Poriferans are loosely organized.

2. They are mostly found in marine water. Only a few are found in freshwater.

3. They are either radially symmetrical or asymmetrical.

4. Their body is usually cylindrical.

5. The scleroblast secretes spicules while spongin fibres are secreted by spongioblasts.

6. They have no organs in their body.

7. They depict cellular grade of organization.

8. The body comprises numerous pores known as Ostia and osculum.

9. The central cavity is called spongocoel or atrium which opens to the outside through the osculum.

10. They reproduce asexually by budding, and fragmentation.

11. The nutrition is holozoic.     

12. Digestion intracellular .            

                                                       type of sponges   phylum porifera 

          Classification of Phylum Porifera

1. Phylum Porifera is classified into three classes:

   Calcarea

   • They are found in marine, shallow, and coastal water.

   • Their skeleton is composed of calcareous spicules made of calcium carbonate.

   • The body is cylindrical and exhibits radial symmetry.

   • The body organization is asconoid, syconoid, or leuconoid.

   • Eg., Clathrina, Scypha or sycon (urn shaped), Leucosolenia(simplest sponge).   

   Hexactinellids

   • They are found in marine and the deep sea.

   • The skeleton is made up of six-rayed siliceous spicules.

   • The body is cylindrical in shape and exhibit radial symmetry.

   • The canal system is Sycon or Leucon.

   • Eg., Euplectella(venus flower blasket), Hyalonema(glass rope).,phenonema(bowal spong).

   Desmospongiae

• They are found in marine or freshwater.

• The body is asymmetrical and cylindrical in shape.

• The canal system is a leuconoid type.

• The skeleton comprises spongin fibres, siliceous spicules, which are monoaxon and triaxon.

• Eg: Spongia(fresh water), Spongilla,Euspongia(both spong) etc.     

                         

Water Canal System in Poriferans      

Types of Canal System in Sponges

• Asconoid canal system: Simplest type of canal system found in Leucosolenia etc.
• Syconoid canal system: More complex than asconoid type, occurring in Sycon etc.
• Leuconoid canal system: Most complex canal system which is common in Spongilla etc.
  • Rhagon type: Leuconoid canal system is derived from a larval stage called rhagon in members of class Demospongiae. Hence, it is named so.   
  • read more https://biologylibrarywith2023.blogspot.com/2023/02/ulothrix-classification-structure-and.html

Modes of Reproduction and Development of Poriferans

Asexual mode

Asexual reproduction in poriferans takes place by means of fragmentation as shown below:

Gemmule formation also occurs in sponges.

Sexual Mode

Sponges reproduce sexually by means of gamete formation followed by the fusion of gametes of opposite sexes. Sponges are usually hermaphrodites, i.e., sexes are not separate.

They undergo internal fertilisation that occurs inside the parental body (female body).

Indirect development is observed in poriferans as development of the embryo into adulthood occurs through intervening larval stages which are morphologically different from the adults. Amphiblastula (in Scypha) and parenchymula (in Leucosolenia) are the larval forms