PORIFERA : Scypha (sycon)

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 Porifera : Scypha (Sycon)

Systematic position:-

Phylum:- PORIFERA

Class :- CALCISPONGIAE

Order :-HETEROCOELA

Family:-SYCETTIDAE

Genus:- Scypha

Habitat:- 

• Marine, colonial, branched and sedentary sponge of cosmopolitan distribution.
• Attached to rocks etc. Just below low tides upto depth of 100 metres in area with strong wave action.
• Commonly called Urn-shaped (due to base like shape) or crown sponge ( due to presence of a crawn like oscular fringe).
• Commonly found species of Scypha are : S. ciliatum, S. elegans and S. raphanus.

Habits:-

 1.) Locomotion:-  

• Absent due to sedentary mode of life.

2.) Feeding:-

•  Omnivores and holozoic . 
• Feeds upon planktons like protozoans, diatoms, bacteria and dead organic particles. 
• Food is drawn inside the sponge body along with a respiratory cum nutritive water current maintained by constant buy uncoordinated beating of flagella of collar cells.
• Digestion is intracellular.

3.) Reproduction:- 

• shows both asexual and sexual reproduction.
• Asexual reproduction occurs by external budding.
• Scypha is monoecious or bisexual or hermaphrodite but always shows cross fertilization due to protogynous condition.
• Fertilization is internal.
• Development is indirect and include a free swimming and ciliated amphiblastula larva for dispersal.

4.) Regeneration:- 

• H.V. Witson reported very hight power of restorative regeneration is Scypha.

Morphology:-

A.) Shape, size, colour and symmetry:-

•  vase like shape,  
• 20-25mm in height,
•  5-6 mm in diameter.
•  Greyish or light brown coloured and 
• radially symmetrical

B.) External appearance:-

• Body surface is with a regular arrangements of polygonal elevations having groups of needle and spear shaped calcareous spicules so giving bristly appearance.
• These elevations are seperated by narrow grooves having groups of small apertures called dermal ostia or inhalent or incurrent pores which lead into a central cavity, called spongocoel, through a system of interconnected canals 
• The spongocoel opens out by a single, wide and circular aperture called osculum or exhalent or excitement pore present at the distal free end of Scypha.
• Osculum is guarded by a funnel shaped collar of long monoaxon spicules called oscular of, which prevents the entry of other animals inside the sponge body through osculum.

Canal system of Sycon:-

Definition:-

 Canal system also called aquiferous system, is a system of interconnected canals of different types present inside the sponge body.

Components of Syconoid canal system:- Scypha has Syconoid canal system and is formed of following parts:-

Dermal Ostia:- 

• Also called inhalent or incurrent pores.
• These are groups of small circular apertures present in the grooves lying between the polygonal elevations of the body surface.
• These are present in a thin pore membrane which closes the incurrent canal externally.
• Dermal Ostia are surrounded by contractile cells, called myocytes, which regulate their opening and closing.
• These act as mouths for ingoing water current.

b) Incurrent canals:-

•  also called inhalent or afferent canals.
• These are narrow be squarish canals.
• Formed by invaginations of surface ectopinacoderm and end blindly on the inner side just outer to spongocoel.

c) Prosopyles(pros.= Near; Pyle= gate) 

• These are short, narrow canals(each about 5mm) which connect the incurrent canals with the radial canals.
• These are intercellular and not intracellular as in Leucosolenia.

d) Radial canals:-

•  Also called flagellated canals.
• These are wider and octagonal canals.
• Each is externally closed just inner to the polygonal surface elevation while internally opens in the excurrent canal by apopyle.
• It is lined by a layer of flagellated cells called collar cells or choanocyte these are formed by evagination of wall of spongocoel of Asconoid canal system.
• The incurrent and radial canals lie parallel and alternate to each other both vertically and radially.
• The arrangement of these canals is such that each radial canal is surrounded by four Incurrent canals and vice versa

e) Apopyle (app=away; Pyle= gate) 

• Also called internal Ostia.
• These are openings of radial canals into excurrent canals.
• Each apopyle is a large circular aperture in the centre of a thin partition called diaphragm lying between the radial canal and excurrent canal.
• It's size can be regulated by contractile cells, called myocytes, which is surrounded by apopyle and regulate it's opening and closing.

f) Excurrent canals:-

• Also called exhalent or efferent canals.
• These are small , wide chambers in which radial canals open. 
• These are lined by pinacocytes and internally open in the spongocoel by wide aperture called gastral ostium.

g) Spongocoel:-

•  Also called paragastric cavity or atrium or cloaca.
• It is narrow and tubular cavity present in the centre of each branch of Sycon.
• It is also lined by flat and polygonal pinacocytes.
• Spongocoels of different branches are continuous at the base.

h) Osculum:-

•  Also called exhalent or Excurrent aperture.
• It is large circular aperture at the tip of each branch.
• It is guarded by a group of monoaxon, needle or spear shaped spicules which collectively form an oscular fringe.
• It is also surrounded by contractile cells, myocytes, which form a kind of sphincter which regulates it's opening and closing

Physiology of canal system:-

• The flagella of collar cells of radial canals undergo constant but uncoordinated beating and maintain a water current which follows following path:-
• Outside water( Dermal Ostia) -- > incurrent canal ( Prosopyles) -- > Radial canals (Apopyles) -- > Excurrent canals ( Gastral Ostia ) --> Spongocoel (Osculum) --> outside.

This ingoing water current helps in following metabolic functione of a sedentary sycon:-

1. Brings food for nutrition.
2. Brings oxygen for respiration
3. Brings sperms of another sponge for reproduction

The outgoing water current also helps in:-

1. Carries out undigested food for egestion
2. Carries out nitrogenous wastes for excretion.

Histology of Sycon:- 

• Histologically the sponge is diploblastic (develops from two primary germ layers).
• Even body wall of adult Sycon is formed of 2layers :
• A) Dermal layer or Pinacoderm
• B) Gastral later or Choanoderm

A) Dermal layer or Pinacoderm:- 

• It is formed of single layer of large, highly contractile, thin, flat, ectodermal in origin and polygonal cells called pinacocytes.
• These pinacocytes are cemented together like the tiles in a floor.
• Each cell has a nucleus in its central swollen part.
• Dermal layer is differentiated into 2 types:-
• Exopinacoderm:-  which covers the outer surface of the body
• Endopinacoderm:-which lines incurrent canals, Excurrent canals and spongocoel.

• Functions:- It provides protection from mechanical injuries and entry of germs.
• It keeps a limit to semi-fluid mesoglea and prevente it's dispersion in water.
• Due to its contractile nature, it shortens it's sponge body to great extent.

Modifications of Pinacocytes:-

• To perform special functions, pinacocytes are modified into following cell types:-
• Porocytes:- also called pore cells.
• These are thin walled, tubular cells present in the inner lining of incurrent canals.
• These are open at both the ends and have tubular intracellular canals called Prosopyles, which connect incurrent canal to radial canal.
• These are present only in young sponge but are absent in the adult sponge.

Myocytes:-

•  These are elongated, fusiform shaped highly contractile cells which are present around the aperture like dermal Ostia, apopyle and oscula.
• These act as sphincter to regulate the opening and closing of these aperture.
• Scleroblasts:- These are modified pinacocytes which means migrate into mesoglea and form calcareous spicules, so are also called calcoblasts

• B) Gastral layer or Choanoderm:- it is the inner lines only radial canals.
• It is formed of large, loosely arranged and flagellated cells called collar cells or choanocytes.

Structure:-

•  Each choanocytes is an oval or rounded cell having vacuolated cytoplasm, single nucleus and a long , whit like vibratile flagellum on its inner side.
• Flagellum arises from a cytoplasmic granules, called centroblepharoplast, a combination of centrioles and blepharoplast.
• It is connected to a darkly stained chromatin body called parabasal body, present on the nucleus, by a fine fibril called rhizoplast.
• These are endodermal in origin.
• The basal part of the flagellum is surrounded by a thin, transparent and contractile collar formed or 20-30 cytoplasmic processes, called microvilli which are about 0.03 to 0.10 micrometer and interconnected by a fibre like material.

Function:-

•  By constant but uncoordinated beating of their flagella, choanocytes maintain a water current for nutrition, respiration, excretion etc. It also secretes mesoglea.

Mesoglea:-

•  Also called mesenchyme or mesohyl.
• It is middle, transparent, non living and gelatinous layer between the Pinacoderm and Choanoderm of body wall of sponge.
• It's matrix is of proteinaceous nature and is mainly secreted by Choanoderm.
• It is of uniform thickness except inner to incurrent canals and outer to Excurrent canals where it thickens greatly to form Gastral cortex and dermal cortex respectively.
• It also has  many free wandering cells on the basis of which mesoglea is called collenchyma or parenchyma.
• These cells of mesoglea are derived either from Pinacoderm or from Choanoderm and are of 2 types:-
• Scleroblasts:-These are modified pinacocytes which means migrate into mesoglea and form calcareous spicules, so are also called calcoblasts
• Amoebocytes:- These are amoeboid shaped cells and are mainly derived from Choanoderm. 
• These move freely in mesoglea.

On the basis of their function, these are of following types:-

• Collencytes or connective tissue cells :- These give rise fine and branched pseudopodia which collectively form a network. These secrete the collagen fibres
• Chromocytes or Pigment cells:- These have loose pseudopodia while their cytoplasm has pigment granules so these give colour to sponge
• Trophocytes or Nourishing cells:- These also have loose pseudopodia and are adapted to ingest, digest and distribute food.
• Thesocytes or Storage cells:- These also have loose pseudopodia and store the reserve food as glycogen, far, glycoproteins or lipoprotein.
• Phagocytes:- These also have loose pseudopodia and engulf and remove the damaged tissue
• Archaeocytes or Embryonic cell gland cells:- These are large sized amoebocytes having blunt pseudopodia. These are undifferentiated or reserve cells and can differentiate into any other cell type depending upon requirement,so these are also called totipotent cells. These also help in regeneration while the gametes forming archaeocytes are called gonocytes.
• Desmocytes or fibre cells:- these are long and slender cells which is present around the longitudinal channels and help in extension of sponge body.

Skeleton of Sycon:-

• Scypha has an endoskeleton of large number of microscopic , crystalline, calcareous and needle-like structures called sclerites or spicules present in the mesenchyme of the body wall . These are always calcareous in nature

1) Types and orientation of Spicules:- 

• On the basis of their number of axes and rays, spicules of Scypha are of two types which are oriented in a characteristic way:-

(a) Monoaxons:-

•  These have only one axis and are of three types:-
• Long, short and spear-like or cube like.
• On the basis of their growth, monoaxon may be monoactinal (or uniradiate) called styles, or diactinal (or biradiate) called rhabds.
• Long monoaxon spicules surrounded and guard the Osculum by forming an oscular fringe.
• Short monoaxons mostly lie parallel to the radial canals.
• Spear-shaped spicules, called oxeotea, are partly embedded in the dermal cortex while partly project out over the polygonal elevations to partly cover and protect the dermal Ostia.

(b) Tetraxons:- 

• These have four aces of growth and are of 2types: tetraradiate and triradiate spicules.
• Tetraradiate Spicules have 4 rays.
• These generally occur in the Gastral cortex along with the triradiate spicules.
• Their one ray projects into the spongocoel.
• Triradiate Spicules are formed by the loss of one ray from the tetraradiate Spicules 
• These generally lie along the radial canals with one ray directed inward.

• (ii) Development of spicules:- Spicules are secreted by special amoebocyte called sclerocytes of mesenchyme which are derived from the modified pinacocytes called scleroblasts of Pinacoderm.
• One scleroblasts secrets only one ray of a spicule so a Monoaxon spicule is secreted by one scleroblast while a triradiate and tetraradiate Spicules is secreted by three and four scleroblasts respectively.
• Scleroblasts secreting calcareous spicules of Scypha are called calcoblasts.

(iii) Development of a Monoaxon spicule:- 

• A scleroblast becomes binucleate.
• A minute and slender axial filament of organic matter is laid between two nuclei which is further deposited with calcium carbonate matter and finally a sheath of organic matter.
• Two nuclei are pushed apart by the growth of spicule and finally the scleroblast is divided into two sclerocytes.
• Inner sclerocytes is called founder as it is responsible for laying and lengthening of the spicule, while outer sclerocytes is called thickener as it deposits additional layers of calcium carbonate so increasing the thickness of spicules.
• CaCO3 used is extracted from the surrounding sea water.
• When the spicule is fully formed, both the sclerocytes leave the spicule, the founder first and the thickener later.

• Development of a triradiate spicule:- A triradiate spicule is secreted by three scleroblast while come together in the form of a figure of a trifoil.
• Each scleroblast becomes binucleate.
• A minute Spicule is laid between two nuclei of each scleroblast.
• Later these spicules act as three rays which finally meet at their inner ends to form a small triradiate spicule.
• Each scleroblast is also finally divided into two sclerocytes so forming a sextet.
• Three thickeners lie at the tip of triradiate spicule and increase the length of rays, while three founders remain joined for some time at the junction of three rays and increase their thickness by adding more layers of CaCO3.

Development of Tetraradiate Spicules:- 

• In the formation of Tetraradiate Spicules, the fourth ray is added to developing triradiate spicule by an additional scleroblast.

(iii) Chemical composition:-

•  Each calcareous spicule is formed of:-
• CaCO3 - 87%
• MgCO3 - 7%
• Water -.   3%
• Small amounts of other minerals.
• An axial thread of organic matter, called spiculin.

(IV) Functions of skeleton:- 

• It provides mechanical support to soft body of sponge.
• It gives definite shape to the sponge.
• It protects the sponge from the wave actions of sea water 
• It helps in resisting external pressure.
• It protects the sponge from other animals due to bristly nature.
• It increases the stiffness of sponge tissue.

Physiology of Sycon:-

• Movement:- Being sedentary in its habitat, Scypha has no active organs for locomotion.
• It has only local contractile powers which are restricted to within 3 to  4 mm of the point of strong stimulus.
• These reactions are slow responses and become noticeable only after one to several minutes of exposure to stimuli.
• As sensory and nerve cells are absent in the sponge body, so these contractile cells acr as independent effectors. 
• The movements of amoebocyte are amoeboid or pseudopodial and not muscular.
• The pinacocytes are highly contractile cells.

Nutrition:- 

• Food:- Scypha is omnivorous Nd holozoic .
• It feeds upon planktons like protozoans, bacteria, diatoms and dead organic Matter.
• So Scypha is microphagous in its feeding.

Ingestion:- 

• Scypha is a filter-feeder. 
• The collar cells or choanocytes maintain a water current by constant but uncoordinated beating of their flagella.
• As the flageller beating is directed towards apopyle, which develops a negative pressure in the radial canals 
• So draw a water current which enters the sponge body through dermal Ostia and reaches the radial canal after passing through the incurrent canals and Prosopyles.
• This incoming water current brings fine food particles along with it as dermal Ostia are very minute apertures, the size of which is further regulated by myocytes.
• The flagella of choanocytes beat from their base to tip, so the water also flows in the same direction. 
• The microvilli of collar of choanocytes act as a filter and the food particles are trapped by these microvilli. 
• The cyclotic flow of protoplasm moves these food partly are trapped by these microvilli.
•  The cyclotic flow of protoplasts moves these food particles towards the base of microvilli from where these are ingested in the food vacuolate by the choanocytes or directly by underlying amoebocyte with the help of pseudopodia. 
• Larger food particles may be ingested by the Pinacocytes lining the incurrent canals.

(iii) Digestion:-

•  Digestion of Scypha is intracellular and occurs in the food vacuole which fuses with the primary lysosome with hydrolytic enzyme to form heterophagosome.
• Medium in the food vacuole is first acidic but finally alkaline. 
• Food vacuole has all the three types of enzymes, Viz. Proteases, carbohydrase and lipase for the Digestion of protein, carbohydrates and fats respectively. 
• But it is not confirmed whether these enzyme's are secreted by Scypha or by bacteria.

Digestion:-

-

•  It may occur by cell to cell diffusion but is generated brought about by special amoebocyte called trophocytes which move about in the mesoglea and distribute nutrients to various cells.

(V) Storage:-

• Reserve food is stored as glycogen, fats , glycoprotein or lipoprotein in the special amoebocytes called thesocytes.

(vi) Egestion :-

•  Choanocytes or amoebocyte, involved in intracellular digestion, throw the indigestible food particles in the radial canals from where these are expelled out along with the outgoing water current.

(vii) Respiration:-

•  Scypha is aerobic in respiration. 
• In this, respiration occurs through general body surface as there are no special respiratory organs and cells of both dermal and Gastral layers are in direct contact with water.
•  This permits direct exchange of gases between oxygen and carbon dioxide of body cells on the principal of diffusion.
•  Wave action ensures the constant supply of well oxygenated water whose importance is evident from that if the dermal Ostia are blocked with debris particles, then the sponges dies.
•  The rate of consumption of oxygen by Scypha has been found to range from 0.04 mL to 0.16 mL per gram of fresh weight per hour.
•  The upper half of the sponge consumes about 10 to 50% more oxygen per gram per hour than the basal half.

(iv) Excretion:-

•  Scypha is ammonotelic but it has no special excretory structures so ammonia of dermal cells lost by diffusion through the body surface in the surrounding sea water while ammonia of Gastral cells is released in the outgoing water current.
•  These wastes are carried away from the sponge by wave action.
• Some science say that the metabolic wastes are taken up by amoebocyte which generally release them into the Spongocoel to be carried out along with the outgoing water current.

(V) Nervous system and behaviour:-

•  Scypha has no special sensory or nerve cells so there is no coordinated actions of the whole body but the cells are sensitive and react individually.
•  This sensitivity is maximally developed at the oscular rim but in other parts the stimuli can be conducted only upto 3 to 4 mm from the point of stimulation so the reactions to stimuli are very slow.
•  These slow and local reactions of sponges are sufficiently to fulfill the needs of sedentary scycon having only cellular organisation.
• The sensitive cells have been found to behave as independent effectors.
•  Some kind of coordination has been reported among the myocytes surrounding the aperture like dermal Ostia, Apopyles and Osculum. These myocytes , surrounding a common aperture, contra simultaneously.
• Tuzet and M Pavan's Dr Ceccatty suggested that the collencytes may act as neurons and form a kind of diffused nervous system connecting the pinacocytes, choanocytes and myocardial.
•  These neurons may receive and conducting the stimuli.

Reproduction:- 

(1) Definition:-

•  Reproduction is the ability of all living organism to produce young ones similar to themselves in many characters. 
• It not only halos in survive but also helps in continuity of that race and group immortality.

(2) Types:-

 On the basis of presence or absence of gametes, reproduction is of two types:- 

(A) Asexual reproduction and 

(B) Sexual reproduction

(A) Asexuality reproduction:-

•   It does not involve formation and fusion of gametes.
•  Scypha reproduces asexually by external budding.
•  In this, multicellular outgrowth, called bud, arise from the base of sponge and develops an Osculum at it's distal end.
•  It may separate from the parent and fix at a new substratum to form a new sponge but may remain attached to the parental body and may develop secondary buds to form a kind of colony.

(B) Sexual reproduction:-

•  It involves formation and fusion of gametes.

(a) Sexes:-

•  Scypha is a bisexual or monoecious and hermaphrodite but it always shows cross fertilization due to protogynous condition.

(b) Gonads:-

•  Gonads in Scypha are temporary as special sex organs are absent. 
• Archaeocytes or sometimes any amoebocyte or sometimes even choanocytes act as gonocytes or gonads to form the gametes.
•  For this the choanocytes lose flagellum, withdraw collar and move into the mesoglea to form the gametes.

(c) Gametogenesis:-

•  It involves formation of gametes.

(1) Spermatogenesis :-

 It involves formation of spermatozoa.

•  In this archaeocytes or amoebocyte or even choanocytes acts as sperm mother cell or spermatogonium.
•  It gets covered by one or more flattened cover cells which are either derived from amoebocytes or formed by the division of spermatogonium .
•  The complex structure so formed is called sperm-nest or spermatocyst.
•  The spermatogonium divides mitotically to form 4-8 spermatocyst, each of which undergoes meiosis to form sperms.
• Each sperm is formed of a rounded or oval head and a long vibratile tail.
•  The tail shows lashing movements which move the sperm in water in search of ovum.

(2) Oogenesis:-

•  It involves formation of ova.
•  In this, archaeocytes or amoebocyte or even choanocytes acts as egg mother cell or oogonium or ovocyte. It migrates in the radical canal, undergoes two mitotic divisions to form 4 oocytes.
•  Each oocyte passes through choanocytes to reach the mesoglea, enlarges in size by engulfing other cells or by receiving nutrition from nutritive trophocytes.
•  When mature oocyte undergoes meiosis and forms one ovum and two polar bodies. 
• During oogenesis, oogonium shows the amoeboid movements.
•  A ripe ovum is a large rounded cell having a large nucleus with a well developed nucleolus.
•  It lies in the wall of radial canal where waits for the sperm of another sponge.

(d) Fertilization :-

•  It involves fusion of gametes and is internal as the egg is fertilised in situ.
•  On maturity, spermatocyst ruptures and sperms are released in the radial canal and are discharged out in the sea water along with outgoing water current through Osculum. 
• The free sperms along with ingoing water current enter into another sponge and reach radial canals.
•  A sperm is taken either by wandering amoebocyte or a choanocytes for which the choanocytes loses its flagellum, withdraws the collar and sinks in the mesoglea to carry the sperm to waiting ovum.
•  Such a choanocytes is called sperm  transient or carrier cell.
• During fertilization, when sperm transient cell comes in contact with ovum, then the later develops a conical depression to receive sperm. Head of sperm swells up and is surrounded by a capsule while it's tail is lost.
•  The capsule with sperm head enters the ovum and forms the zygote.
•  So fertilization in Scypha is internal.
•  Later the zygote us surrounded by a brood capsule formed by aggregation of amoebocytes.

Development of Embryogeny:-

• Development of Scypha started within the brood capsule and occurs in situ.
•  It involves following steps:-

(a) Cleavage :-

•  It involves the transformation of a single celled zygote into a single layered hollow spherical blastula large by rapid mitotic divisions of Zygote.
• Cleavage in Scypha is holoblastic and unequal.
•  It starts when the Zygote lies in the mesoglea of the sponge.
•  First three cleavages are vertical or meridional and produce a pyramidal disc of eight cells called blastomeres.
•  Fourth cleavage is horizontal or equatorial and slightly above the equator so producing a sixteen celled stage.
•  At this stage, the blastomeres are arranged in two tiers, each formed of 8 blastomeres.

 Depending upon size, blastomeres are of two types:- 

(1) Micrometres:-

•  It forms the upper tier of 8 cells . These will form the Choanoderm.

(2) Macromeres:-

•  It forms the lower tier of 8 cells.
•  These lie towards the parent Choanoderm.
•  These will form the Dermal layer.
• The Macromeres donot divide for some time while Micrometres divide by rapid mitosis to increase their number, become columnar and develop inward directed flagella.
•  Later , a blastocoel or segmented cavity is developed between the tiers of blastomeres.
•  The Embryo is now called blastula.
• (b) Formation of stomoblastula:- Macromeres become rounded, granular and develop a blastopore between them which communicates with the blastocoel.
•  Blastopore acts as mouth and is used to ingest the surrounding amoebocyte for nutrition.
•  This feeding blastula like larva is called stomoblastula and is the parasite on its parent.
•  It's wall is formed of many small, elongated and flagellated Micrometres and 8 spherical and granular Macromeres 
• (c) Formation of amphiblastula:- Stomoblastula undergoes inversion so the flagella of micromere are now directed outward.
•  Now the Macromeres multiply grow on all sides and close the mouth.
•  Now Embryo elongates, ruptures the brood capsule and is released outside through radial canals, Excurrent canal, spongocoel and Osculum.
•  This free larva is more or less oval shaped.
•  It's wall is half flagellated of small and narrow flagellated Micromeres and half non-flagellated of large Macromeres and is called amphiblastula.
•  It is formed in the development of most of the members of O. Calcarea .
•  It swims freely in sea water keeping its flagellated pole forward, so helps in dispersal of a sedentary adult sponge.

(d) Formation of Gastrula :-

•  After a brief free-swimming period, flagellated half gets surrounded by non-flagellated micromeres.
•  This produces a two layered Gastrula larva having a newly formed cavity which opens out by blastopore at the invagination end.
•  In Gastrula, outer layer is formed of non-flagellated and granular Macromeres while inner layer is formed of small and flagellated Micromeres.
•  So gastrulation is opposite to inversion.

Metamorphosis:-

•  Metamorphosis involves the transformation of Gastrula larva into a young sponge.
•  During this, gastrula fixes itself to some substratum by its blastoporal endz elongates and becomes cylindrical.
•  Blastopore is closed by growth of both cell- layers while free end develops a perforation called Osculum.
•  During metamorphosis outer non-flagellated Macromeres flattern to form dermal layer of Pinacocytes and their derivatives like myocytes porocytes and calcoblasts while inner flagellated Micromeres form Gastral layer of choanocytes and line whole of central cavity representing future spongocoel.
•  Certain dermal cells act as porocyte and develop intracellular Prosopyles which act as dermal Ostia. 
• Young sponge now resembles the adult Asconoid Leucosolenia and is called Olynthus stage .
•  Mesoglea is developed between the dermal and Gastral layers and is mainly secreted by Choanoderm, so the sponge wall thickens .

 Now this Olynthus stage is transformed into young Syconoid Scypha by following changes:- 

•  (1)  Incurrent canals are formed by invagination of dermal layer.
• (2) Radial canals are formed by evagination of Gastral layer. The  formation of radial canals start from the middle of the body.
• (3) incurrent canals GT external bounded by pore membrane having intercellular dermal Ostia.
• (4) Choanocytes are restricted in only radial canals.
• (5) Scleroblasts and various amoebocyte are developed in mesoglea. Scleroblasts and myocytes are derived from the dermal layer while archaeocytes and other amoebocyte are Developed from the Gastral layer. So the mesenchymal cells are derived both the Embryonic layers.

Peculiarity in development:-

• Development of Scypha is characterized by certain peculiar features like:-
• (1) Blastula of Scypha is called Stomoblastula as it has mouth to ingest amoebocytes.
• (2)Blastula undergoes inversion.
• (3) Development includes a partly flagellated and partly non-flagellated amphiblastula larva.
• (4) Gastrulation occurs by invagination.
• (5) Most peculiar feature of development of Scypha is that the flagellated Micromeres and non-flagellated Macromeres form the Gastral and dermal layer respectively.
•  It is exactly reverse to the mode of Development in higher animals in which the flagellated and non- flagellated cells of gastrula give rise to outer ectoderm and inner endoderm respectively.
•  So two layers of a sponge gastrula cannot be called ectoderm and endoderm, and two layers of adult sponge cannot be named epidermis and gastrodermis as in coelenterates.