Porifera:

Characteristics of Porifera:

The wide-ranging characteristics of porifers are as follows:

i) There are few cell differentials but no organization of tissues.

ii) Body has 2 layers.

iii) All live in sea or river bottoms.

iv) Their body has no evenness.

v) There is only 1 cavity.

vi) Have many openings (pores) all over body wall.

vii) Has the skeleton made up of calcium silica or horny fibres.

viii) There is no distinguished nervous system

ix) Fresh water ones reproduce even sexually.

x) Reproduce asexually by promising and aggregation of cells to form gemmules.

xi) They are hermaphrodites.

xii) Have huge regenerative power.

This is described as dead end phylum. It is believed that they have not given rise to any other group of organisms.

Physical Structure of Porifera:

Generally the extensive sheet of formless tissue. Some are vase-shaped anchored by the narrow base to the base in sheltered waters happen in several colors. Contain odor of sulphur. Few are small others are huge. Few include supporting tissue composed of calcium, silicon or horny tissues. Simplest type of sponges is the vase-shaped living tissue joined by its base to bottom of sea. It has the internal cavity with the opening on top. Body wall is composed of cells located in outer, inner and middle, between outer and inner cells. Each of the 3 groups of cells carries out different tasks. Cells lining cavity have flagella that beat to drive out water through aperture of vase known as osculum. Food particles and water get in cavity through several pores on body wall. Pores are preserved by pore cell whose protoplasm can develop to close or contract to open pore. Spore also manages rate of water inflow in it through the procedure also. The other method is to narrow or close osculum. The two methods are not handled by body of animal but role as dictated by external conditions like, acidity of water around. Collar cells with flagella beat separately and constantly in reply to temperature of water within sponge. Other cells simply line out body of sponge. Only some of body cells and collar cells obtain food by diffusion of digested particles. There is requirement for food to be transported to other cells not within vicinity of where food is assimilated. Non-feeding cells are other cells separately from collar cells, some body cells that get food materials directly and are in position to digest it. Non-feeding cells require to be supplied with food transported from site of digestion, or are close to feeding cells, to attain food by diffusion. Middle cells in intermediate region, lying between inner flagellate layer and outer epidermis have many types of cells -wandering amoebocytes and archeocytes. Amoebocytes more in amoeboid manner. Archeocytes are unspecialized and are able of taking on numerous roles. These 2 groups of cells serve as distributors of nutritive material to those cells of sponge which are not able to move about or get the food directly.

Organic Structure of Porifera:

The organism beaten by water currents constantly must have the adaptation to endure the current. This is done by sponge's skeleton composed of fibrous organic substance known as sponging. In some it is made by calcareous or siliceous crystalline spicules secreted by specialized cells known sclerocytes. Adjacent spicules produce to make particular structural arrangement that result in very complicated architectural support within sponge wall. Few like glass sponge develop the spiral course for the fine siliceous ties in the skeletal frame work. Therefore in the light structure, the tough most times beautiful skeletal frame is created for sponge for enduring water currents.

Reproduction of Porifera:

Fresh water sponges reproduce sexually by making eggs and sperm. They also perform so by making small round masses of cells called gemmules (in cold or drought) in protective cases known as spicules. These grow into new sponges when conditions are favorable. Archeocytes are liable for forming gemmules by combining together. They are also liable for forming outside layer and water channels of the novel sponge as they initially come out of spicules in favorable condition. Archeocytes which come out next form collar cells. Last archeocytes stay within and persist as archeocytes. You will thus observe how cells here achieved special functions by the position. Notice versatile nature of archeocyte to turn out to be any type of cell which is required. Cells also combined to form new sponges when in experiments mature sponge is broken into constituent cells. Though, cells of epidermis for instance, in former animal congregate to create epidermal ones in new aggregate and so on. This is the good ability to redevelop itself.

The sponges have been useful for approx 500 million years living at bottom of water. It has benefit in those which have developed in large size - to such the extent that they can wave in sufficient food for themselves. They are just the multicellular group with little or no coordination. The elongated contractile cells around the oscular react separately to outside situation to slowly contract to close opening. There is no nervous link between or among cells, hence no nervous system. Sponges stand on their own. They don't appear to have given rise to recognized multicellular group.

Size and Complexity of Porifera:

a) Sponges signify animals of great antiquity. Several basic problems arise with larger size which could have simply studied from sponges. With raise in size, there is the requirement for support for protoplasmic mass engaged in size. We may suppose that this has been ensured by existence of skeletal re-enforcement of organic fibrous material known as sponging, as in horny sponges; other kinds of skeletal material are of silicon or are calcaneous.

b) Large organisms frequently require to move about to make sure they can situate right kind and quantity. This sponge doesn't do. It handled to spread out below sea and with the mass spread manages to get adequate to survive.

c) Sponge has no systems for digesting food it take in. It is satisfied with services of mobile cells in carrying digested food to those cells which are not feeding cells.

d) Same amoebocytes are liable for forming gemmules in unfavorable season.

e) Extremely significantly an animal which must survive and flourish must be sensitive to the surroundings and have the resources of self defense. All of these are at extremely ancient level or non-existent at all.

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