Phylum Porifera (Sponges)MAIN CHARACTERISTICS
Animals of this phylum show following important characters.
Most simple multicellular organisms. From evolutionary point of view they occupy a position between protozoa and true metazoa
HABIT AND HABITAT
- Mostly marine but few in fresh water habitat.
- They are sessile, living attached to rocks, coral and other hard surfaces
- Their shape may be cylindrical, branching, globular, flat, bell shaped or cup shaped.
- Some are dull in colour and most are brightly coloured.
- The body is perforated by pores and canals.
Most of sponges contain following types of cell:
Forming the epidermis.
Form pores of the body wall
These are flagellated cells, form the internal lining of the body. These cells are strikingly similar to the choano flagellates.
- Much of the body is composed of jelly like matrix containing a skeleton made of Protein, CaCO3 or silica.
- Sponges are organized on cellular level, instead of a single cell carring on all the life activities.
- Sponges show cellular differentiation but little or no coordination of cells to form tissues.
- They usually have an endoskeleton of separate spicules.
- They do not posses a head, an interior end, a mouth or gut cavity.
- They are sedentary organisms ranging in size from 1 to 200cm.
Digestion takes place with in the cell. (Intracellular)
PROCESS OF FEEDING, EXCRETION AND RESPIRATION
- Sponges feed by filtering out bacteria and fine particles of organic matter from water.
- The flagella of “Choanocytes” beat and create a current of water.
- The water current also helps in respiration, removal of waste products and dispersal of gametes.
- Reproduction is of both type asexual and sexual
- Asexual reproduction is by means of “Buds” and “Gemmules formation”.
- Sexual reproduction is by means of sperm and ova.
- All sponges appear to be diploid and have the usual metazoan process of “Oogenesis” and “Spermatogenesis”.
- The eggs retained just beneath the choanocytes where they are fertilized by sperm from another sponge brought in with the current of water.
- Fertilization is internal.
- After cleavage, the larva escape from the parent to the open sea as a free swimming “Amphiblastula larva”.
- It finally becomes attached to the bottom by its anterior end.
- Reproduction is also by fragmentation.
Body cavity is known as “Spongocoel”.
Common examples are