1. ZLY 103 Phylum Porifera SHITTU, Olalere Department of Zoology
University of Ilorin
Nigeria

2. Introduction - The Sponges
The Phylum Porifera (Latin pours, pore + ferra, to bear) are primitive pore-bearing multicellular organisms. They are sessile and aquatic, usually abundant in the marine with a few freshwater species. They differ from other metazoans and the colonial acellular animals, hence they were classified as parazoa, a sub-kingdom that appears to form an evolutionary dead end. The common diagnostic characteristics are:
There are no definite organs and systems for the coordination of the body functions because the cells do not form perfect tissues; they are mere loose aggregations of independent cells.
With the exception of the vase-shaped forms that are asymmetrical, many species grow irregularly in a plant-like manner forming flat globular or branching structures without symmetry.
The body wall is composed of three layers, the outer, gelatinous middle and inner layers. The middle layer consists of numerous

3. Introduction - The Sponges
Cells and various shapes of calcareous or siliceous internal skeleton (spicules) or organic fibres (spongin) or both.
The gut is absent; the only internal space (paragaster or spongocoel), usually in form of cavities, pores, canals and chambers, form structures through which water flows.
Reproduction is by sexual ad asexual means, except that they do not form gonads.
There are various shapes and sizes of sponges but the basic structure of the canal system is of three types; the Ascon, Sycon and Leucon types.

4. The Sponges – Body Plan

5. The Sponges Canal Types
Asconoid Type
It is a simple structural type, where pores (incurrent pores) on the body surface open and lead water directly into the spongocoel (Lined with choanocytes – collar cells). The movement of water through the pores to the osculum is influenced by the small size of the pores and the larger size of the osculum. Present only in Calcarea E.g. Leucosolenia, Clathrina canariensis.

6. The Sponges Canal Types
Syconoid Type
It is an intermediate structural form modified from the asconoid form. The body wall is folded into finger-like processes such that between the two projections of the body wall, there are alternating incurrent pores ad radial canals connected by thin pores (prosopyles). The choanocytes appear only in small radial canals. Water, therefore flows from outside through incurrent canals, the prosopyles and radial canals to spongocoel flowing out through the osculum, e.g. Grantia species , Calcarea, hexactinellida.

7. In flux & Out flux of Water in Syconoid

8. The Sponges Canal Types
Leuconoid Type
It is the most complex structure formed possibly to compensate for increase in body weight and size. The incurrent and radial canals have out-folding to form many small chambers to which the choanocytes are restricted. Meanwhile, the spongocoel is completely obliterated or transformed into water channels leading to the osculum. This type of canal exists in three grades, viz; eurypylous, aphodal and diplodal, e.g. Spongilia species.

9. The Sponges - Leucosolenia
This is a small and simple sponge found attached to shore rocks, weeds and other submerged objects in the sea. Each colony is about 2cm high and sac like in shape with a centrally located spongocoel.
The colony of Leucosolenia is whitish yellow in colour. In the simplest species of Leucosolenia, the colony consists of few simple vase-like, cylindrical individuals each terminating in an osculum and united at their bases by irregular horizontal tubes. Most species are more complicated, consisting of a confused network of branching tubes from which stand out a few larger erect cylinders bearing an osculum at their summit.

10. The Sponges - Leucosolenia
Body wall
The body wall is thin and consists of an outer epidermis, the pinacoderm and an inner endodermis, the choanoderm separated by a jelly-like non-cellular layer of mesenchyme or mesogloea, enclosing a central cavity, the spongocoel.
Pinacocytes:- This is the outer epithelial layer made up of closely fitted flat polygonal cells. It is perforated at different intervals by canals (ostia) bound by large pore cells – porocytes. Porocytes regulates the inflow of materials into the spongocoel.
Choanoderm:- This is lined with oval-shaped, flagellated choanocytes. The base of the flagellum is encircled by a ring of microvilli (about 0.2um in diameter) known as collar or fence. Each microvillus is about 0.2um apart and interconnected by fine strands to form a mesh-like structure. The choanocytes are useful cells that ensure steady flow of water through the spongocoel, and also for feeding and respiration.
Mesohyll:- The gelatinous middle layer is a layer that separates the outer layer from the inner one. It consists mainly of amoebocytes (diff. shapes & sizes). Some amoebocytes especially the sclerocytes and Thesocytes are for skeleton formation and food storage respectively. The enclosed spicules are of taxonomic importance and comes in different shapes and sizes. They are responsible for protection, form framework and stiffen the sponge.

11. The Sponges - Leucosolenia
Leucosolenia Colony Longitudinal Section Choanocytes
flagellum
Nucleus
Collar microvilli
Food Vacuole

12. The Sponges - Leucosolenia

13. The Sponges - Leucosolenia
Biology:- Leucosolenia feeds on tiny organisms and degenerating organic materials suspended in water streaming into the central spongocoel through the pores. As the water passes through the spongocoel, the choanocytes beat the flagella (in an uncoordinated manner) to create water currents. These are subsequently drawn through he meshes of the collar to filter out the suspended food particles. The latter are carried to the base of the collar where they are enclosed as food vacuole. The digestion of food materials occur intracellularly in the food vacuole and the digested products are passed to the adjacent amoebocytes for storage. The undigested materials are passed into the water that streams out of the body through the osculum.
There is no special organ for respiration and elimination of metabolic wastes. Dissolved oxygen in the surrounding water enters the body through the surface cells by simple passive diffusion. Excretory products of ammonia are discharged similarly. However, the amount of oxygen available for consumption is dependent on the rate of water flow and it is also dependent on the osculum size.
Leucosolenia reproduces asexually by budding – a process whereby a single sponge germinates horizontal branches that later develops into new individuals.

14. Leucosolenia – Asexual Reproduction
However, the formation of gemmule (a reproductive unit) remains the commonest form of asexual reproduction during adverse conditions.
A gemmule develops from the yolk laid by a group of archaeocytes in parent sponges. It is a flask shaped structure consisting of an anteriorly situated outlet (micropyle) and a central mass of amoebocytes surrounded by protective membranes and coat armed with spicules (amphidisc). During unfavourable conditions, gemmules undergoes a nuclear division as the parent body dies away. During favourable condition, amoebocytes sprouts through the micropyle to become a new sponge body.

15. Leucosolenia – Sexual Reproduction
The process of sexual reproduction involves male and female sex cells, which are either formed from amoebocytes or by transformation of choanocytes. Unlike the metazoans, fully developed male cells (sperms) swim to first locate the choanocytes, the carrier cells, which absorb and carry them to the ova for fertilization to occur. The resultant zygote undergoes holoblastic cleavage and cell arrangements to form blastula. This embryo soon become stomoblastula as the middle part of the non- flagellated cells opens as a ‘mouth’ while the other part with flagellated cells invaginate towards the blastocoel. The stomoblastula, through this process of inversion, turns its inside (through the mouth) outside such that the flagellated cells now form the anterior pole. This embryo is called amphiblastula – a motile larva of the Calcarea. A completely developed amphiblastula larva in the maternal mesenchyme or choanocytes is forced through the radial canal and the spongocoel to the exterior where it swims freely for few hours or days before it undergoes another process of transformation known as gastrulation. During this process, a reversal of the inversion at the stomoblastula stage occurs such that the flagellated cells invaginate inward and become covered by non-flagellated cells. The latter form the epidermis and the spicule secreting cells (Scleroblasts) as the flagellated cells become the choanocytes.

16. Leucosolenia – Sexual Reproduction

17. End of Presentation Thanks for Listening