Phylum Porifera
Prepared by : Nada H. Lubbad
 Porifera characteristic
o Sponges are primarily marine, (less than 2% of all sponge species are found in freshwater).
o They are cellular - level organization:
- Cells are specialized (functional).
- Cells are not organized into tissue.
- Parazoans ( tissue are not true)
- No systems for reproduction, digestion, respiration, sensory, excretion.
o Radially symmetrical or asymmetrical.
 Structure of sponges
o A sponge is a rigid perforated bag.
o The empty space of this bag is called the spongocoel.
o It has three layers :
- Inner layer : It is lined with flagellated cells called choanocytes or collar cells.
Functions of the collar cells :
 They generate currents that help maintain circulation of seawater within and through the
sponge.
 They capture small food particles.
 They capture incoming sperm for fertilization.
- Mesohyl layer: a gelatinous, non living layer of material is lining by amoeboid cells called
archaeocytes or amoebocytes.
Functions of archaeocytes :
 Responsible for digesting food particles captures by the choanocytes.
 Some store digested food materials.
 It may gives rise to both sperm and eggs.
 Develop into more specialized cell type when necessary.
 Can specialized to secrete the supporting elements located in the mesohyl layer.
The sponges are supported by spicules:
 It may be calcareous (CaCO3) or siliceous spicules (SiO2) or fibers composed of a
collagenous protein called spongin.
 The cells secreting spicules are termed sclerocytes and those producing spicules fibers
are termed spongocytes.
 Both of these cells are derived from archaeocytes.
Function of spicules & fibers :
 In species identification.
 Maintain the shape & prevent predation.
- Outer layer : flattened contractile cells (Pinacocytes). These cells also line the
incurrent canals and the spongocoel in some places where choanocytes
are lacking.
Contraction of Pinacocytes has the functions :
 Enable sponge to undergo minor shape change.
 Regulating water flow through the sponge by varying the diameter of incurrent
openings.
 water flow into the spongocoel through narrow openings called the Ostia & exits
the spongocoel through larger opening called osculum .
 Reproduction in sponges:
1. Asexual :
o Internal buds.
o Regeneration: can regenerate from broken pieces.
o External buds (Gemmules) : Produced in winter as dormant bodies ,coat and
supportive cells protects from freezing and desiccation.
2.Sexual:
o It takes place in in the mesohyl.
o usually hermaphroditic with male and female gametes , formed by amoebocytes.
o most hermaphroditic species produce eggs and sperm at different times so they do not
self fertilize.
o sperm is released into environment via osculum and is brought in by another sponge via
Ostia.
o Sperm captured by collar cells, which then lose there collar & transform into specialized
amoeba-like cells that carry sperm to the egg.
o Fertilized egg develops into blastula , which is release into water (in most )
o The larvae may settle directly & transform into adult or may be planktonic for a time
o Larvae are lecithotrophic = use stored yolk
 Porifera diversity
• There are 3 basic levels of sponge construction:
1. Asconoid.
2. Syconoid.
3. Leuconoid.
Asconoid :
o The most primitive and simplistic in structure.
o They are a perforated tube shaped.
o Radial symmetry.
Syconoid (scypha) :
o next level of complexity.
o typically vase shaped ( tubular ) like the asconoid
sponges.
o Larger than Asconoid.
o walls are invaginated , thicker & the pores
penetrate it are longer forming a system of
simple canals.
o radial symmetry
Leuconoid :
o The highest level of complexity in sponges.
o lost radial symmetry and are very irregular in shape and
may attain large sizes.
o invaginated canals are even further invaginated and
folded to from small flagellated chambers.
o Water moves through the canals into these chambers
and out via central canal and osculum.
Class Calcarea:
o Have spicules made of calcium carbonate.
o Mostly small in size.
o All species are marine.
o Representatives of all 3 types of construction occur in this class.
Class Demospongiae
o Members of the largest class.
o this class containing 80% of all sponge species.
o The supporting spicules and fibers may be composed of spongin and silica but never
of CaCO3.
o All freshwater sponges are found in this class.
Class Hexactinellida
o (Hyalospongiae).
o It contains sponges whose bodies are supported by 6-rayed siliceous spicules.
o Sponges known as glass sponges are marvels of structural complexity and
symmetry.
Class Sclerospongiae
Coralline sponge
o Most of them live in deep water on corals reef
o Sclerospongiae is no longer considered a class.
o CaCO3 foundation with SiO2 spicules
o