Phylum Porifera -- B.Sc. - I Theory

 Phylum Porifera

The phylum porifera meaning pore bearing animals. The term is coined from Latin –Porous –pore ferre- to bear . The body surface bears pores.

General characters. 

1.    They are aquatic animals found in freshwater some are marine forms.
Colonial or solitary forms attached to the rock, shells, or other solid objects. 
2.    They are diploblastic, multicellular animals
3.    They consist of outer ectoderm and inner endoderm.
4.    Between ectoderm and endoderm  gelatinous mesogloea is present.
5.    Mesogloea contains different types of amoeboid cells.
6.    The shape of the body is vas shaped or cylindrical, symmetrical or asymmetrical.
7.    The surface of the body shows minute pores called ostia.
8.    Toward the free end large opening is presently called osculum.
9.    The body cavity encloses a large cavity called spongocoel.
10.    The canal system is well-developed consists of the incurrent canal, excurrent canals.
11.    The body is supported by calcareous or silicic spicules and spongin fiber.
12.    Digestion is holozoic and intracellular.
13.    Reproduction is sexual as well as asexual.
14.    Regeneration power is very high.
15.    Fertilization is internal.
16.    Cleavage is holoblastic.

Phylum porifera consists of three classes these are
1.    Class 1 - Calcaria
2.    Class 2 – Desmospongia
3.    Class 3 –Hexactinellida

Class 1 - Calcaria 
 1.    They are exclusively marine animals.
2.    They are called calcareous sponges.
3.    They are solitary or colonial forms.
4.    These are diploblastic animals. Consists of ectoderm and endoderm.
5.    The body is vas shaped,  radially symmetrical consists of many cylinders.
6.    Skelton consists of spicules of calcium carbonate.
7.    The spicules are monoaxon, di-axon, tetra-axon.
8.    Canal system may ascon, sycon, or simple leucon type.
9.    The choanocytes are larger.
10.    Reproduction is sexual as well as asexual.
11.    Asexual reproduction by budding
12.    The free living larva is called amphiblastula.
Ex. Sycon or scypha, Grantia, Leucosolenia, etc.

Class 2 – Desmospongia

1.      They are marine as well as some are freshwater forms.

2.      They are multicellular primitive animal.

3.      The sponges are massive and brilliantly coloured.  

4.      The body is asymmetrical.

5.      The skeleton is formed of silicic acid, sponging fibers or both. In some forms skeleton is absent.

6.      The canal system is of leucon type, euryphylus, aphodal or diphodal.

7.      Asexual reproduction by gemmules.

8.      The larval form is called sterogastrula.

Ex. Spongilla is the best example of freshwater sponge., Chaina, Bath sponge, etc.  

Class 3 –Hexactinellida

1.      They are popularly known as glass sponges.

2.      The body is symmetrical, cylindrical, vase-shaped. The size ranging from 10 to 30 cm in height.

3.      The canal system is euripylus leucon type.

4.      The choanocytes are smaller in size.

5.      The skeleton is made up of silicic acid consists of 6 rayed or hexactine spicules.  The spicules are of two types. Larger spicules are called megascleres and smaller are called microscleres.

Ex. Hylonema, Eupectella

Canal system of Sycon/ scypha.

The sycons are pore bearing animals. The presence of the canal system is unique characteristic of sycon.  The body of sycon shows the presence of various kinds of canals. These canals together form a canal system.  The canal system of sycon is of the specific type called as syconoid type of canals system.

The canals system of sycon consists of the following parts.

a.       Ostia

b.      Incurrent canal

c.       Radial canal

d.      Excurren canal

e.       Spongocoel

f.       Osculum

 a. Ostia:

These are minute pores of aperture present on the surface of the body also called dermal ostia or dermal pore. The ostia leads into incurrent canals.

b.    Incurrent canal:

Dermal ostia lead into narrow somewhat square incurrent canal. The inner end of the incurrent canal is closed. The incurrent canals are lined by ectodermal cells which are called pinacocytes.  Each incurrent canal leads into the radical canal through a connection called as prosopyle.   The prosopyle is lined by porocytes which are nothing but the modified pincocyte.

c. Radial canal :

These are finger-like octagonal projections open into the spongocoel through the excurrent canal. The radial canals are arranged radially around spongocoel also called radial canals. The outer end of the redial canal is closed blindly.. The radial canal show presence of flagellated choanocyte , hence redical canal or radial chamber is called a flagellated chamber. 

The incurrent and excurrent canals lie alternately.  The incurrent canals communicated with a redial canal through a connection are called apopyle.  The apopyle is lined with myocyte (Muscle cells) which regulate closing and opening of apopyle.

d.    Excurrent canal :

the excurrent canal is the short and wide passage between redial canal and spongocoel.  Excurrent canal connects with a radial canal with spongocoel.

e.   Spongocoel :

It is a large space enclosed by each cylinder of sycon called as spongocoel or perigastric cavity lined by pinacocyte. The spongocoel opens out by a wide opening present at the distal end of the cylinder called as osculum through which water is thrown outside of body .

Course of circulation of water

The Canal system of sycon plays a very important role in the physiology of sycon.  Incoming water brings oxygen, food and reproductive bodies. While outgoing water carries out undigested food, nitrogenous waste, carbon dioxide, etc.

                                                   

The course of the circulation of water is taking place as follows.

1.      Water from outside into incurrent canal through ostia.

2.      From incurrent canal water enter into radial canal through prospyle.

3.      Water from the radial canal into the excurrent canal through apopyel.

4.      Water from excurrent canal into spongocoel.

5.      Water from spongocoel to outside of the body through osculum.
 

Role/ Significance  of Canal System:

Canal system in  sycon performs many functions and plays very important role in the life of sycon.  Incoming water brings oxygen, food and reproductive bodies. While out going water carries out undigested food, nitrogenous waste, carbon dioxide etc.

 Nutrition:

The sponges are holozoic animals. The incoming water current brings microscopic organism as food such as protozoans, bacetria, diatoms and organic food particles. The food is digested by choanocytes present in flagellated chamber or radial canal. Thus it perform function of nutrition in sycon.

 Respiration:

Along with incoming water current oxygen enters inside body of sycon and exchange of  respiratory gases takes place between cells of sycon. Out going water gives out carbon dioxide from body. 

 Excretion:

The metabolic waste such as ammonia, urea, uric acid and other nitrogenous waste product are removed from body along with outgoing water current.

 Reproduction:

The incoming water current brings sperms which are captured by the choanocytes and help in fertilization.