Chapter - 11
Phylum Porifera (Sponges)
MAIN CHARACTERISTICS
Animals of this
phylum show following important characters.
NATURE
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
SHAPE AND STRUCTURE
§ 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.
MICROSCOPIC STRUCTURE
Most of sponges
contain following types of cell:
(A) PINACOCYTES
Forming the
epidermis.
(B) POROCYTES
Form pores of the
body wall
(C) CHOANOCYTES
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
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
§ 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.
LARVA
§ 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
Body cavity is
known as “Spongocoel”.
EXAMPLES
Common examples are
1. Sycon
2. Euplectella
3. Euspongia
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