Sponges ( Sponges fall into 3 groups based on body organization)
1)Asconoids;are small , simple forms with a tube-shaped body
2)Syconoids;also have a tubular body whose wall is much thicker and highly folded into a series of incurrent canals that deliver water into radial canals lined with choanocytes.
3)Leuconoid:the largest and most complex ones
-permits for an increase in body size
ntroduction to Phylum Porifera
"Sponges are the simplest multicellular animals. Because the cell is the elementary unit of life, the evolution of organisms larger than unicellular protozoa arose as an aggregate of such building units. There are many advantages to multicellularity as opposed to simply increasing the mass of a single cell. Since it is at cell surfaces that exchange takes place, dividing a mass into smaller units greatly increases the surface area available for metabolic activities. Thus multicellularity is a highly adaptive path toward increasing body size."
Major Characteristics of Phylum Porifera
Multicellular; body a loose aggregation of cells of mesenchymal origin;
Body with pores (ostia), canals, and chambers that serve for passage of water;
All aquatic; mostly marine;
Symmetry radial or none;
Epidermis of flat pinacocytes; most interior surfaces lined with flagellated collar cells (choanocytes) that create water currents; a gelatinous protein matrix called mesoglea contains amebocytes, collencytes, and skeletal elements;
Skeletal structure of fibrillar collagen (a protein) and calcareous or siliceous crystalline spicules, often combined with variously modified collagen (spongin) fibrils;
No organs or true tissues; digestion intracellular; excretion and respiration by diffusion;
Reactions to stimuli apparently local and independent; nervous system probably absent;
All adults sessile and attached to substratum;
Asexual reproduction by buds or gemmules and sexual reproduction by eggs and sperm; free-swimming ciliated larvae.
Sponges are differentiated by the type of canal system
Asconoids – Small and tube shaped. Water enters through microscopic dermal pores into a large cavity called the spongocoel, which is lined with choanocytes. The choanocyte flagella pull the water through the pores and expel it through the single osculum.
Syconoids – Syconoid sponges also have a tubular body and single osculum, but the body wall is thicker and more complex. Water enters through incurrent canals that deliver it to radial canals, which are lined with choanocytes. The radial canals then empty into the spongocoel, which is lined with epithelial cells and not with choanocytes.
Leuconoids – Leuconoid sponges have the most complexity and are the best adapted for increase in sponge size. Most leuconoids form large colonial masses, each member of the mass having its own osculum, but individual members are poorly defined and often impossible to distinguish. Clusters of flagellated chambers are filled from incurrent canals and discharge water into excurrent canalsosculum. that eventually lead to the
So now students, these are the detail notes of Porifera for your HSEB exams. Read it carefully and post your suggestions.
First Aristotle observed them.
John Ellis in 1765 recognised them as animals. In 1825 Robert Grant gave them the name Porifera.
Habit: they are low multicellular, cellular level, no tissue, marine, few freshwater, all aquatic, solitary or colonial, all sessile.
Body form: vase like (Scypha), cylindrical (Leucosolenia), tubular or cushion shaped.
Symmetry: radial or asymmetrical.
External morphology: body perforated by pores, ostia, and an exhalant osculum having oscular fringe, body wall has oxeotes or spicules. A central cavity spongocoel or paragastric cavity is present.
Body wall: Diploblastic, with outer pinacoderm and inner choanoderm enclosing gelatinous non cellular mesenchyme having skeletal elements and free amoeboid cells.
Canal system: this is complex system of pores and canals; body wall is folded forming alternating invaginations and evaginations. Various components are- ostia or dermal pores, myocytes can reduce pores. Incurrent canals (invaginated folds of body wall) end blindly at inner ends. Pinacocytes line them.
Prosopyles- incurrent canal communicated with radial canals through intercellular spaces known as prosopyles.
Radial canals- corresponding evaginations, lined by flagellated choanocytes. Incurrent and radial canals are parallel.
Apopyles- opening of radial canals into spongocoel.
Spongocoel, central cavity is lined by choanocytes (Leucosolenia), not lined (Scypha).
osculum is provided with spincters( lined by myocytes)
Example in Geodia apopyle is drawn out as a narrow canal- aphodus.
In Oscarella, prosopyle is drawn out as a narrow canal- prosodus.
Canal system: these are of three types:
I. Ascon type: in Leucosolenia. Incurrent pores/ostia→through mesenchyme→lead into spongocoel (lined by coanocytes) →open outside by osculum.
II. Sycon type: in Scypha/ Sycon, this is folded version. Incurrent canal, parallel to each other, dermal ostia→incurrent canal (on flagellated) →prosopyles (intercellular species) →radial canal (flagellated) →apopyles→spongocoel→osculum.
III. Leucon type/ rhagon type: in Spongilla, further folding, flagellated chambers are small and spherical cavities, excurrent canal are developed. Ostia–incurrent canals (not lined by choanocytes) →prosopyle→flagellated chambers (lined by choanocytes) → excurrent canals (much developed) →osculum (out). Spongocoel reduced and branches as excurrent canals.
Cellular organization- there is 2 cell layers:
pinacoderm- this is divided into –
a) Exopinnacoderm- covering entire body except ostia and osculum.
b) Endopinacoderm- lining of incurrent canals and spongocoel.
Pinacoderm has Pinacocytes.
Choanoderm- called gastral epithelium, collar cells/ choanocytes, arranged loosely over mesenchyme, cells have single nucleus, one or two contractile vacuole, food vacuole, reserve food, blepharoplast, rhizoplast, and a single basal granule or kinetosome from which originate a flagellum, surrounded at its base by thin cytoplasmic collar.
Mesenchyme/ mesohyle- contain many amoebocytes which are modified archeocytes.
They are of following types:
a) Archeocytes- undifferentiated, blunt pseudopodia, large nucleus, produce other cells, sex cells, role in regeneration, totipotent.
b) Collenocytes- branching pseudopodia, united into syncytial network, are connective tissue or collencyte.
c) Chromocyte- has pigment with lobose pseudopodia.
d) Thesocyte- food reserve, storage cells, lobose pseudopodia.
e) Myocytes- contractile around ostia,
f) Scleroblast- manufactures spicules and according to nature of products are called calcoblast, silicoblast and spongioblast.
g) Germ cells- ova and sperms.
Skeleton- in mesenchyme, secreted by sclerocytes produced by Scleroblast, known as spicules.
Spicules- are crystalline, spine or rays radiate from a point, have a core organic material around which deposited either calcium carbonate (calcite) or colloidal silica. So two types, calcareous and siliceous.
Larger spicules – megascleres.
On the basis of number of axes-
a) Monoaxon- grows along one axes. In one direction only-monoactinal, if in both directions- diactinal. Both are calcareous and siliceous.
b) Tetraxon- four rays pointed in different directions (usually one ray is elongated), when all rays are equal, known as calthrops. When all four rays persists, known as tetraradiate/ quadriradiate. When one ray is lost, then called triradiate.
c) Triaxon- 3 axes cross one another at right angle to produce six rays, thus known as hexactinal( class hexactinellida)
d) Polyaxon- several equal rays are radiating from a central point, star like.
Development: secreted by sclerocyte- a monoaxon spicule ex- is secreted by a group of two sclerocytes, one thickener cell, other founder cell, thickener cell lays down CaCO3
Spongin-organic, horny, elastic, scleroprotein, containing sulphur and chemically related to collagen, insoluble, chemically inert, resistant to protein digestion.
Nutrition: filter feeder, by collar cells, form food vacuoles, digestion intracellular, first acidic then alkaline, amoebocyte distribute food, food is stored in thesocytes.
No respiratory, no excretory system. Contractile vacuoles in some freshwater forms help in excretion. Largely ammonia is excretory product.
Reproduction: both asexual as well sexual
asexual: following type;
a) Budding – numerous archeocytes collect at surface of pinacoderm bulges out to form bud.
b) Fission- hypertrophied over a limited area, disconnected.
c) Reduction bodies- many marine and freshwater sponge disintegrate, leaving small rounded balls, known as reduction bodies, consists of internal mass of amoebocytes covered externally by pinacoderm.
d) Gemmule- these are internal buds, unfavorable conditions, formed by aggregation of archeocytes, which secrete thick hard chitinous inner and thin outer membranes, scleroblasts secrete siliceous spicules, monaxons or amphidiscs(laid radially) between two membranes. Membrane is pierced at one end for outlet known as micropyle.
Sexual reproduction- hermaphrodite, sperm and ova derived from archeocytes or choanocytes which undergo gametogenesis, protogyny (Scypha). Cross fertilization and internal fertilization.
Spermatogonium (enlarged archeocytes) surrounded by one or more flattened cover cells to produce spermatocyst.
Oocyte moves like an amoebocyte and grows by engulfing other cells which may be amoebocytes or special nurse cells (trophocytes), undergo two maturation division to form ovum, lying in wall of radial canal.
Spermatozoa enter first a choanocytes which lies adjacent to a ripe ovum, looses tail, and swollen head becomes surrounded by capsule, choanocytes also becomes amoeboid (known as carrier cells), carrier is received by invagination of egg, sperm head penetrates into egg.
Embryogeny: cleavage- zygote begins development in mesenchyme, equal and holoblastic cleavage, first three divisions are vertical resulting into 8 blastomeres, 4th division is horizontal, forms 16 blastomeres formed, tier of 8 cells macromers( form pinacoderm) and other tier, micromere form choanoderm, micromeres undergo rapid mitosis, forming several micromeres that acquire flagella at their inner sides, now called blastula with a blastocoel, also called stomoblastula or coeloblastula, this under go inversion(turns out through mouth), so flagella are directed towards outside, now known as amphiblastula, micromeres at anterior part. Amphiblastula passes out, swims, and settles, macromers multiply rapidly, flagellated half of larva invaginated into and overgrown by granular non flagellated half, becomes a typical double walled gastrula with a blastopore at the invaginated side.
Post larval period or metamorphosis- larva fixes to substratum by its blastoporal end and lengthens into a cylinder, at free distal end of which opens osculum. Several performations become ostia, outer non flagellated granular cells gives rise to dermal epithelium or exopinnacoderm and to scleroblasts and porocytes. Inner flagellated cells develop choanoderm and give rise to functional choanocytes, archaeocytes and other amoebocytes. Mesenchyme cells are thus derived from both embryonic layers.
Sponges have high power of regeneration.
e.g. Euplectella- Venus flower baskets
Hylonema – glass rope, glass sponge
Cliona- boring sponge
Chalina- dead man’s finger or mermaid’s gloves
Euspongia- bath sponge
Spongilla- fresh water sponge.
On basis of skeleton, 3 classes
Class 1. Calcarea or calcispongeae
i. Calcareous spicules.
ii. Spicule are monoaxon, triaxon, tetra axon
E.g. Leucosolenia, Sycon or Scypha, Grantia
Class 2. Hexactinellida or hyalospongiae
i. Skeleton of siliceous spicules are triaxon or six rayed.
e.g. Euplectella, Hylonema
Class 3. Demospongeae
ii. Skeleton of spongin fibre or spongy fibre with siliceous spicules or skeleton may be absent.
iii. Spicules either monoaxon or tetra axon (may be 8 rayed but never 6 rayed.E.g. Euspongia, Spongilla, Cliona, Chalina.