Phylum Porifera| general characteristics| Diagram| MCQ of Porifera| Terminal question of porifera|

 Phylum Porifera 

 Members of phylum Porifera or sponges are most primitive of metazoans or multicellular animals. It includes more than 5,000 species. They appear to be quite life-less and plant like. 

Porifera are a conspicuous and colorful component of many seascapes. 

General characters: -

1. Porifera is multicellular organisms. 
2. All are marine with few exceptions (A single family of freshwater species. e.g., Spongilla). 
3. Its shape some time cylindrical, branching, globular, brightly or dull in colour, they are orange, red, yellow or green colour.
4. Solitary or colonial. 
5. The body is perforated by pores and canals but lack other organs (mouth or nervous system).
6. Body is asymmetrical or radially symmetrical. Body surface has numerous pores, the ostia, serving for inflow of water. 
7. The water current passes through ostia into the chambers and the central cavity and finally comes out of the body through terminal aperture, the osculum. 
8. Body wall has outer pinacoderm (dermal epithelium), inner choanoderm (gastral epithelium) and gelatinous non-cellular mesenchyma in between. 
9. No definite organ for feeding and digestion. 
10. Digestion is intracellular. 
11. The water current serves to bring food organisms and oxygen in the body and carry away the excretory and reproductive products. 
12. Cells are loosely arranged and do not form definite layers. Thus are not truly diploblastic
13. Choanocytes (flagellated collar cells) usually line special chambers.
14. Choanocytes are present only in sponges. 
15. Sensory and nerve cells absent. 
16. Each cell is directly stimulated and transmits sensations to other cells also. 
17. Development is indirect through free swimming ciliated larva, the amphiblastula or parenchyma.
18. All sponges are hermaphrodite. 
19. The sexual reproduction occurs by the sperms and ova but asexual reproduction by buds or gemmules.
20. Sponges have great power of regeneration. 
21. Sponges are cultivated for commercial purposes.
22. About 10,000 species of sponges are known in the world.

 Scypha or Sycon

Classification: 

PHYLUM - PORIFERA 

CLASS - CALCAREA 

ORDER - HETEROCOELA 

GENUS - SCYPHA 

Habit and Habitat: -

Scyphy or Sycon is commonly called as ‘urn sponge or crown sponge’ because of its 

typical shape. Scyphy or Sycon is marine sponge.This has been found widely in nature. It 

is found attached to submerged rocks in shallow water near coast. It occurs solitary or as 

branching colonial form. Several species of Scyphy are S. elegans, S.ciliatum, 

S.lingua and S. gelatinosum etc.

Structure: -

External morphology: -

Shape- The colony has the appearance of a branching tree. It consists of two to several cylindrical branches connected together to a stolon at their bases. The latter is attached to substratum. Each cylinder is vase like.

Size- The size of a cylinder varies from 2-8cms. 

Colour- The sponge presents various shades of grey or light brown colour. 

Osculum and oscular fringe: The free distal end of each cylinder has wide opening, the osculum or exhalent pore. It is surrounded by numerous straight needles like calcareous spicules arranged in a circle. 

Dermal pores or ostia: - 

Body surface of Sycon has regularly arranged polygonal elevations separated lines or furrows. In furrows present numerous apertures, the ostia or inhalant pores and open into current canals. 

Entire body surface has spicules protruding out from it. 

Canal System in Sycon: -

Sycon, like all other sponges, possesses the characteristic peculiarity-the canal system. The body wall of sponges is folded to produce complex system of pores and canals for entrance of water current. Scypha or Sycon represents Sycon type of canal system. 

Its components are: -

• Ostia or dermal pores- The external body surface is covered by thin pore membrane.  It bears two or more openings, the ostia or the dermal pores. The pores are surrounded by myocytes. These can reduce the diameter of dermal pores and thus reduce amount of incoming water. These open into incurrent canals.
• In current cannels- These are narrow spaces placed radially between adjacent radial canals. These are lined with pinacocytes and opens outside by ostia.
• Prosopyles- Incurrent canals communicate with radial canals by prosopyles.
• Radial or flagellated canals- The body of Sycon invaginates to form thimble-shaped chambers. Chambers are lined by flagellated choanocytes and called flagellated chambers or radial canals. The radial canals and incurrent canals lie parallel and alternate to each other and are separated by mesenchyme. Radial canals end at their outer ends but open into spongocoel.
• Apopyles- The openings of radial canals into spongocoel are called apopyles or gastric ostia.
• Spongocoel- It’s the large central cavity into which radial canals open through apopyles. The choanocytes line radial canals and spongocoel is lined by flattened pinacocytes. Spongocoel is central space all along the length of body. 
• Osculum- The spongocoel opens to outside by a terminal opening, the osculum. Osculum is surrounded is surrounded by a contractile myocyte. These form a sphincter which regulates the rate of water flow.

Mechanism of water circulation: 

 The water current is produced, and water is pumped into the body by beating of flagella of choanocytes which line the radial canals. A wave of spiral undulations passes from base to tip of each flagellum and water is pushed in. Water enters the body by ostia into incurrent canals, from there by prosopyles into radial canals and then by apopyles it reaches spongocoel and discharge into exterior by osculum. In other way, the path of water into the canal system can be represented as following: -

Step 1) Water from outside 

Step 2) Dermal ostium 

Step 3) In current canal 

Step4) Prosopyle 

Step 5) Radial canal 

Step 6) Apopyle

Step 7) Excurrent canal 

Step 8) Gastic ostium 

Step 9) Para gastric cavity

Step 10) Psculum 

Step 11) Exterior

Importance of water circulation of canal system: - 

Water current plays a very important role in the physiology of the sponges. The water circulation system helps the sponges in nutrition, digestion, respiration, excretion and reproduction. The water current brings in food and oxygen and it takes away waste products.

1. Nutrition: -Scypha feeds on particles of organic matter and small living organisms, like a diatoms, bacteria and protozoa; they are drawn in the water current. 
2. Digestion- It is entirely intracellular, as in protozoa. Partly digested food is taken up by amoebocytes in which digestion is completed, the amoebocytes transport and supply the digested food to all parts of the body. 
3. Respiration- The Gaseous exchange occurs by simple diffusion, between the cells of sponge and the current of water. Water entering body is rich in oxygen and facilities exchange of gases. The rate of consumption of Scypha was found to range from 0.16 ml.of oxygen per gram of fresh weight per hour in the smaller specimens to 0.04ml. in the larger ones.
4. Excretion- While outgoing, water current removes CO2 and nitrogenous products.
5. Reproduction-The spermatozoa enters body of other sponges along water current.

Reproduction in Sycon: -

The sponges reproduce both asexually and sexually. 

Asexual Reproduction –

Asexual reproduction occurs throughout the Porifera. The asexual reproduction takes place by budding, regeneration and gemmule formation. 

a) By budding - During favorable conditions Sycon reproduces by budding. The buds arise basally near its attachment and then constrict off after some time to lead independent existence. 

b) By regeneration - Sponges have a great power of regeneration. They not only replace parts lost during injury, but any piece of body can grow into complete sponge. The process is however very slow and is completed in months or years. The regeneration power is used for cultivation of bath sponge industrially.

Sexual Reproduction -

Both male and female gametes are formed inside body of same animal (hermaphrodite) Gametes 

develop specialized amoeboid cells, called archeocytes found in mesenchyme. 

• Spermatogenesis-sperms are produced from amoebocyte or spermatogenesis and get surrounded by one or more flattened cells cover cells. The spermatocyte divides two to three times and cells develop into sperms. Mature sperm has round head with nucleus and long tail.
• Oogenesis- Oocyte is differentiated into an enlarged amoebocyte with nucleus. It increases in size, stores food material, is nourished by choanocytes called trophocytes or nurse cells. Its nucleus undergoes two maturation divisions (meiosis) to form ovum. 
• Fertilization- The fertilization is internal and cross fertilization occurs. The sperm does not enter directly in the ovum but reaches a radial canal and is dispersed by the water currents. Sperm cell enters the nurse cells or choanocyte adjacent to mature oocytes, which becomes amoeboid and fuses with ovum liberating the sperm. The nuclei of ovum and sperm fuse and form zygote.

Development of Sycon: -

1. Cleavage- The divisions are holoblastic and development occurs inside the body of sponge. The 1st three divisions are vertical and produce pyramidal plate of 8 cells. The 4th division is horizontal and divides blastomeres unequally into 8 micromeres and 8 macromers. A cavity develops in between, and embryo enters into the blastula phase. Micromeres divide more rapidly and develop flagella at their free ends, while macromere becomes rounded and represents the Stom blastula.
2. Stom blastula- One side of Stom blastula is composed of many small, elongated, flagellated micromeres, while other side composed of 8 rounded, non-flagellated macromeres. Inner cavity (blastocoel) opens outside through the mouth. It is used to engulf the surrounding amoebocytes for nutrition.
3. Amphiblastula- The Stom blastula undergoes inversion and flagellated ends of flagellated cells comes to lie to the exterior. The flagellated Stom blastula is called amphiblastula larva. The fully formed amphiblastula is set free into radial canal. It escapes by osculum along the water current and leads free swimming existence and undergoes gastrulation by invagination and emboly. The flagellated cell invagination into blastocoel and macromere grows over them by rapid multiplication. Thus, gastrula is formed.
4. Gastrula- Gastrula has two-layer bodies. Outer layer is granular, ectoderm and inner are non-granular flagellated cells, endoderm. The central cavity opens outside by opening called blastopore.
5. Metamorphosis (Post embryonic development) - The gastrula adheres to substratum like rock, sea weeds, etc., by its blastoporal end and undergoes metamorphosis to form adult Sycon.

• The larva lengthens into a cylinder and develops osculum at free distal end. 
• The non-granular flagellated cells of endoderm form choanocytes. 
• The granular non-flagellated cells of ectoderm give rise to pinacocytes of dermal epithelium. 
• The body wall gets perforated by Ostia and Olynthus stage is attained by Sycon. The choanocytes are shifted in these radial canals and the body wall increase in thickness, the adult Scypha is formed and its colony develops. 

Objective Question of Phylum Porifera: -

1) Most primitive group of animals, which are multicellular is: -

(a) Coelenterata  (b) Sponge (c) Nemertine (d) None of these 

2) In case Demospongiae, leucon type of canal system is derived from: -

(a) Ascon type of canal system of larva (b) Rhagon type of canal system of larva (c) None of these (d) Both a and b

3)Animal of phylum Porifera are characterized by: -

(a) Gland cell (b) Choanocytes (c) Amoeboid cell (d) All of these 

4)Ascon type of canal system is formed in: -

(a) Euspongia (b) Leucosolenia (c) Amoeboid cell (d) None of these 

5) Which one of the sponges is harmful to the oyster industry?

(a) Cliona (b) Euspongia  (c) Spongilla (d) All of these 

6) Venus Flower Basket is the name of the dried skeleton of: -

(a) Euspongia (b) Spongilla (c) Euplectella (d) all of these 

7)Which of the following is a freshwater sponge?

(a) Spongilla (b) Euplectella (c) Euspongia (d) None of these 

8)The simplest type of canal system in Porifera: -

(a) Leucon type (b) Radial type (c) Ascontype  (d) All of these 

9)Porifera is characterized by the presence of: -

(a)Para gastric cavity (b) Coelenteron (c) Coelom (d) None of these 

10)In Poriferan skeleton secreting cell are: -

(a) Amoebocytes (b) Thyrocytes (c)Archeocytes (d) All of these 

11)Correct sequence of evolution of canal system if sponges are: -

(a) Sycon - Ascon - Leucon (b) Ascon - sycon - Leucon (c) Sycon - Leucon - Ascon (d) Ascon - Leucon - Sycon 

12)Member of phylum Porifera are: -

(a) Mostly marine animal, few being freshwater (b) Exclusively marine animal (c) Mostly fresh water few being marine (d) Exclusively freshwater animals.

Answer Key: -

(1) b (2) b (3) b (4) b (5) a (6)c(7) a (8) c (9) a (10) b (11) b (12)a

Terminal Question: - 

1. Write the outline classification of Phylum Porifera?

2. Into how many classes is Phylum porifera divided? Write their names and important characters?

3. What is the characteristic feature of phylum Porifera based? 

4. On basis of which characters is the classification of Porifera based?