FSc Notes Class XI Biology Phylum Porifera (Sponges) 1st Year Biology Notes Online Taleem Ilmi Hub Class 11

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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

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

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