B.Sc.
Zoology Part I
CHARACTERS AND CLASSIFICATION OF PHYLUM PORIFERA
multicellular organisms with cellular grade of organization without well-defined
tissues and organs: exclusively aquatic; mostly marine, sedentary, solitary of
colonial animals with body perforated by pores, canals and chambers through
which water flows; with one or more internal cavities lined with choanocytes; and
with characteristic skeleton made of calcareous spicules, siliceous spicules of
horny fibers of
General Characters:-
Porifera are all aquatic, mostly marine except one family spongillidae
which lives in freshwater.
They are sessile and sedentary and grow like plants.
Body shape is vase or cylinder-like asymmetrical or radially symmetrical.
The body surface is perforated by numerous pores, the ostia through which
the water enters the body and one or more large openings, the oscula by
which the water passes out.
Multicellular body consisting of outer ectoderm and inner endoderm with
an intermediate layer of mesenchyme, therefore diploblastic animal.
The interior space of the body is either hollow or permeated by numerous
canals lined with choanocytes. The interior space of sponge body is called
spongocoel.
Characteristic skeleton consisting of either fine flexible spongin fibers,
siliceous spicules or calcareous spicules.
Mouth absent, digestion intracellular.
Excretory and respiratory organs absent.
The nervous and sensory cells are probably not differentiated.
The sponges are monoecious; reproduction both by asexual and sexual
methods.
Asexual reproduction occurs by buds and gemmules.
The sponges possess high power of regeneration.
Sexual reproduction occurs by ova and sperms.
Fertilization is internal but cross fertilization occurs as a rule.
Cleavage holoblastic, development indirect through a free-swimming
ciliated larva called amphiblastula or parenchymula.
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The organization of sponges has been grouped into three main types, viz;
ascon type, sycon type and leuconoid type due to simplicity in some forms
and complexity in others.
Classification:-
The classification of Porifera is based chiefly on types of skeleton found in
them.
CLASS I: CALCARIA OR CALCISPONGIAE
(L; calx= lime) or (L; calx= lime + spongos= sponge)
They are commonly called calcareous sponges.
Skeleton consist of monaxon or triradiate and tetraxon spicules of calcium
carbonate.
They are dull coloured sponges less than 15 cm in size.
They are solitary or colonial; body shape vase-like or cylindrical.
They may show asconoid, syconoid or leuconoid structure.
They occur in shallow waters in all oceans.
Asconoid sponges with radially symmetrical, cylindrical body.
Spongocoel is lined by choanocytes.
Syconoid or leuconoid sponges having vase-shaped body.
The body wall is thick and folded, choanocytes line only radial canals.
Asexual reproduction by budding. The free swimming larva is called
amphiblastula.
Example: Leucosolenia, Clathrina, Sycon or Scypha, Grantia.
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CLASS II: HEXATINELIDA OR HYALOSPONGIAE
(G; hyalos= glassy + spongos= sponge)
They are called glass sponges.
Skeleton is of siliceous spicules which are triaxon with 6 rays. In some the
spicules are fused to form a lattice-like skeleton.
There is no epidermal epithelium.
Choanocytes line finger-shaped chambers.
They are cylindrical or funnel shaped and are found in deep tropical seas,
they grow up to one meter.
Spicules are hexasters, i.e. star-like in shape.
Radial canals or flagellated chambers are simple.
They are not attached by root tufts but commonly attaches to a hard surface.
Spicules are amphidiscs. No hexasters.
They are attached to the substratum by root tufts.
Example: Euplectella ,Hyalonema.
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CLASS III: DEMOSPONGIAE
(Gr; demos= frame + spongos= sponge)
Contains the largest number of sponge species. Large-sized, solitary or
colonial.
The skeleton may be of sponging fibers or of sponging fibers with siliceous
spicules or there may be no skeleton.
Spicules are never six-rayed, they are monaxon or tetraxon are
differentiated into large megascaleres and small microscleres.
Body shape is irregular and the canal system is of leucon type.
Generally marine, few freshwater forms.
Sponges are mostly solid and simple rounded cushion like flattened in
shape usually without branches.
Skeleton comprised mainly of tetraxon siliceous spicules but absent in
order myxospongida.
Canal system is leuconoid type. Shallow water form.
Simple structure.
Skeleton absent.
Spicules are not differentiated into megascleres and microscleres.
Asters may be present.
Spicules are differentiated into megascleres and microscleres.
Example: Spongilla, Chalina, Spongia.
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Economics Importance of Phylum Porifera
(Sponges)
Sponges play a vital role in the economic and
commercial growth of our society. some sponges
are used in the bath because of their skeleton.
the followings are the uses of sponges.
1. Man uses the skeleton of sponges for
washing and bathing. Many artificial
sponges have been made from synthetic
material. But still, there is much demand
for the natural sponge. It is an important
industry in any part of the world. The best
commercial sponges are found in the warm
water of the Mediterranean Sea.
2. Sponges have a great capacity to absorb
water. So they are used in surgical
operations for absorbing fluid and blood.
3. Sponges are also used for sound
absorption in buildings.
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4. during the cultivation of radish and other
fast-growing seeds and food items,
sponges are used to maintain agriculture
on a large scale.
5. for the quick sprouting out of seeds in
agriculture, sponges are used as a
moistened. it creates a container around
the seed.
6. to avoid cracks, it is also used as a box with
fragile things to protect them from having
cracks on them. which provides softness
and safety against being breakable.
7. sponges play an important role in catching
the oil leaks. they are wrapped up with
some tools to hold them safely so that
8. they are also used to try the inside of the
vase by putting it in a stick.
9. by mixing it in soaps and detergents, it
saves soaps from melting fast, more ever,
putting sponges on the soaps, it can suck
extra water which caused the melting
down of the soap.
10. it can be used to eliminate stink odor
from the refrigerator by sprinkling it a
small amount.
11. by putting some sponges on the base of
wares, it can avoid wares from scratches.
12. it is also used to remove sticking
wallpapers from the walls just because
of soaking the sponges into the water and
vaping it over the wall with the help of
stubborn left paper.
13. used as a scrub while taking bath.
