Unit 1
Kingdom Protista
General characteristic and
Classification Up to Classes,
Locomotory Organelles and Locomotion in Protozoa
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Protista
Protista is a kingdom to which
the eukaryotic microorganisms, protists belong. Protista was first observed by
John Hogg in 1860s as primitive unicellular forms of both plants and animal. At
that time, this kingdom was known as 'Protoctista', which literally means first
established beings. Later in the year 1866, the term Protista was coined by
Ernst Haeckel. This kingdom belongs to the domain Eykarya. Recent
classifications are being made by scientists where listing of organisms is done
on hierarchical basis. They have different characteristics that distinguish
them from other kingdoms, but the boundaries of this kingdom are not well
defined. This kingdom forms a connecting link with the others dealing with
plants, animals and fungi. The most common examples Protista include, Amoeba, Plasmodium, Paramecium, slime
mold, red, brown and golden algae, fungi, diatoms, etc.
General Characteristics of Protista
·
They
are mostly unicellular but some are multicellular like algae and colonial
organisms.
·
They
are with or without a cell wall. If cell wall is present it is composed of
cellulose.
·
They
are either free-living or parasitic.
·
They
have (9+2) arrangement of flagella (In flagellates) and have membranous
organelles.
·
They
are grouped into 3 categories: plant-like, fungus like and animal like
(protozoa).
·
According
to the categories, they have different modes of nutrition, like heterotrophy or
autotrophy, holozoic, saprophytic or parasitic mode of nutrition.
·
Plant-like
protists (algae) have chlorophyll and accessory pigments, named xanthophylls,
phycobilins, and carotene.
·
Most of the protists
live in water, some in moist soil or even the body of human and plants.
·
These organisms are
eukaryotic, since they have a membrane bound nucleus, with nucleoplasm,
nucleolus, helical DNA, chromosomes and other membrane bound organelles such as
mitochondria, chloroplast, endoplasmic reticulum and G. complex etc.
·
Nuclei of protists
contain multiple DNA strands; the number of nucleotides is significantly less
than complex eukaryotes.
·
Movement is often by
flagella or cilia.
·
Protists are
multicellular organisms; they are not a plant, animal or fungus.
·
Respiration - cellular
respiration is primarily aerobic process, but some living in mud below ponds or
in digestive tracts of animals; they are strict facultative anaerobes.
·
Flagellates are filter
feeding, some protists feed by the process of endocytosis (formation of food
vacuole by engulfing a bacteria and extending their cell membrane).
·
Reproduction - some
species have complex life cycle involving multiple organisms. Example: Plasmodium. Some reproduce sexually
and others asexually.
·
They can reproduce by
mitosis and some are capable of meiosis for sexual reproduction.
·
They form cysts in
adverse conditions.
·
Some protists are
pathogens of both animals and plants. Example: Plasmodium falciparum
causes malaria in humans.
·
Protists are major
component of plankton.
Classification of Kingdom
Protista
Kingdom Protista are categorized into following taxons:
Plant-like Protists - ALGAE
Plant-like
protists have chlorophyll like that in plants. The green substance in their
cells enables them to make food by photosynthesis. They produce and
release oxygen like the plants. It is believed to be the most supply of oxygen
on Earth is from the plant-like protists. The plant-like protists are the major
food source and primary producers for aquatic organisms.
ü
Phylum Chlorophyta (Green
Algae) -
The green algae include unicellular and multicellular algae. They are mostly
fresh water. Body is sheet-like thallus. They have cell walls made of cellulose
and pectin. Food is reserve starch which is stored in pyrenoids. Example: Spirogyra - it is a unicellular
green alga, it grows as a green thread or filament.
ü
Phylum Rhodophyta (Red
Algae) -
Red algae are mostly large and multicellular. They grow in oceans. The algae
'Nori' and Gelidium are used as food, in parts of Asia. Carragean and agar are
glue-like substances in red-algae. Agar is used as a medium used for growing
bacteria and other organisms under laboratory conditions. Agar is also
used to make gelatin capsules and a base for cosmetics. Carragean is used as a
stabilizer and thickener in dairy products. It is also used in toothpaste to
give its creamy texture.
ü
Phylum Phaeophyta (Brown
Algae) - Brown
algae are multicellular. They grow on rocks in shallow water of the
sea. Large brown algae are called kelps. Kelps may grow densely in the sea
and form kelp forests. They form important food sources for fish and
invertebrates. The brown algae growing on rocks are known as rockweed. Example
of rockweed is Sargassum. Algin
is a substance derived from some algae which is used in making ice cream,
lotion and plastics.
ü
Phylum Chrysophyta (Golden
algae) -
'Chryso' means 'color of gold'. There are three types of golden-algae:
yellow-green algae, golden brown algae, diatoms. Diatoms are the most abundant
and are found in seawater and freshwater habitats. The shells of diatoms are
made of silica. They are major source of food to may aquatic organisms. The
shells of fossil diatoms form thick deposits on the sea floor known as
'diatomaceous earth'. It is used as water filters, abrasive and to add
sparkling to products such as paint and fingernail polish.
ü
Phylum Pyrrophyta (Fire
Algae) - It
contains of species of one-celled algae called dinoflagellate which means
'spinning swimmers'. They store food in the form of starch and oils. The red
color is due to chlorophyll a and c and xanthophylls. These organisms have
ability of bioluminescence. Almost all species like in marine water. Some
species causes the 'red tide phenomenon'. Gonyaulax
is a genus of dinoflagellates with the type species Gonyaulax spinifera Diesing. Gonyaulax
belongs to red dinoflagellates and commonly causes red tides, which contain a
neurotoxin and are poisonous to marine fauna.
Fungus-like Protists – SLIME MOULDS
Slime molds- Slime
molds are saprophytic protists. They are very bright in appearance. They
live in moist soil, decaying plants and trees. They are single-celled
organisms. During favorable condition they form multicellular aggregations
called plasmodium. During unfavorable conditions, plasmodia differentiate to
form fruiting bodies bearing spores at the tip. These spores’ posses resistant
true walls, which help in survival for a long time during adverse conditions.
These spores disperse by air currents.
Animal-like Protists - PROTOZOANS
Protists
that have resemblance to animals are known as protozoans. They are live in
moist and watery environments. The characteristics similar to animals and
plants are - their ability to move and their inability to produce their own
food (heterotrophs). They differ from animals being unicellular while animals
are multicellular.
It
seems improper to call protozoan organisms as “animals” because sometimes it is
difficult to tell whether the members are plants or animals, as they are
intermediate forms having both plant and animal characteristics. Common examples
are Euglena and Volvax having chlorophyll, which are considered
animal by zoologists and plants (algae) by botanists. On the basis of presence
or absence of chlorophyll, these two genera would be placed separately in plant
and animal kingdom, respectively, which seems unrealistic. Further, some
dinoflagellates have cellulose cell wall like plants, but do not have
chlorophyll and are holozoic. It would not be proper to describe some
dinoflagellates as plants and others as animals.
One
solution to these difficulties is to remove the protozoans from animal kingdom
and place them under a new kingdom, called protista, along with some algal and
fungal groups. This was done by Haeckel (1866) who created protista, and by
Whittaker (1969) who proposed 5 kingdoms including Protista. In the kingdom
Protista, the different classes of Protozoa (Falgellata, Sarcodina, Sporozoa
and Ciliata) become independent phyla. However, in the present textbook, we
will consider Protozoan representing a single phylum of animal kingdom,
according to the old, classical or traditional concept, which is still adopted
by most protozoologist as well as textbooks.
Phylum
Protozoa is a large and varied group and poses a number of problems in its
classification. The following classification of Protozoa is based on the scheme
given by the committee on Taxonomy and Taxonomic Problems of the Society of
Protozoologists and mainly proposed by B. M. Honigberg and others (1964). It
divides Protozoa first into 4 subphyla:
1) Sarcomastigophora 2) Sporozoa 3) Cnidospora and 4) Ciliophora
Subphylum
I Sarcomastigophora
·
Locomotor organelles
pseudopodia or flagella or both.
·
Nuclei of one kind
(monomorphic).
Superclass
(A) Mastigophora (Flagellata)
1) Simple, primitive, with
firm pellicle.
2) Locomotor organelles
flagella.
3) Nutrition autotrophic or
heterotrophic or both.
Class 1 Phytomastigophorea (Phytoflagellata)
1) Chlorophyll bearing
chromatophores present.
2) Nutrition mainly
holophytic by phototrophy.
3) Reserve food starch or
paramylon.
4) Flagella 1 or 2,
sometimes more.
Example: Euglena
Class 2 Zoomastigophorea
1) Chlorophyll or
chromatophores absent. Mostly parasitic.
2) Nutrition holozoic or
saprozoic.
3) Reserve food glycogen.
4) Flagella one to many.
Example: Leishmania
Superclass B Opalinata
1) Entire body covered by
cilia like flagella.
2) Nuclei two to many,
monomorphic.
3) Reproduction by
symmetrogenic binary fission or by syngamy of anisogametes.
4) Parasitic mainly found in
frogs and toads.
Example: Opalina
Superclass C Sarcodina (Rhizopoda)
1) Body mostly amoeboid
without definite pellicle. Some with a skeleton of some kind.
2) Locomotion by
pseudopodia.
3) Nutrition holozoic or
saprozoic.
Example: Amoeba
Class 1 Rhizopodea
Pseudopodia as lobopodia, filopodia or reticulopodia
without axial filaments.
Example: Amoeba
Class 2 Actinopodea
Pseudopodia mainly axopodia with axial filaments, radiating
from a spherical body.
Example: Actinophrys
Class 3 Piroplasmea
Small parasites in red blood cells of
vertebrates.
Example
– Babesia formally included in
Sporozoa, but its species do not produce spores.
Subphylum II Sporozoa
Locomotor
organelles absent. Spores usually present. Exclusively endoparasitic in nature.
Class 1 Telosporea
Spores
without polar capsules and filaments, naked or encysted.
Example:
Plasmodium
Class 2 Toxoplasmea
Spores absent. Only asexual
reproduction.
Example: Toxoplasma
Class 3 Haplosporea
Spore cases present. Only asexual
reproduction.
Example:
Ichthyosporidium
Subphyllum III
Cnidospora
Spores with polar filaments present.
Class 1 Myxosporidea
1) Spores
large, developed from several nuclei.
2) Spores
with two or three valves.
3) Parasites
mostly in fishes.
Example:
Myxidium
Class 2 Microsporidea
1) Spores
small, developed from one nucleus.
2) Spores
with a univalved membrane.
3) Intracellular
parasites in arthropods and fishes.
Example: Nosema
Subphyllum IV
Ciliophora
·
Presence of cilia as
locomotor and feeding organelles at some stage in the life cycle.
·
Nuclei of two kinds
(dimorphic).
Class 1 Ciliata
1) Locomotor organelles numerous hair like
cilia, present throughout life.
2) Definite
mouth (cytostome) and gullet present except in a few parasitic forms. Anal
aperture (cytopyge) permanent.
3) One or more contractile vacuoles present
even in marine and parasitic types.
4) Mostly two kinds of nuclei, large
macronucleus and smaller micronucleus.
Example: Paramoecium
Locomotory
organelles and Locomotion in Protozoa:
Locomotor organelles in Protozoa include pseudopodia,
flagella, cilia and myonemes;
1) Pseudopodia:
Pseudopodia are temporary structures form by the streaming
flow of cytoplasm. Sarcodina move with this structure. On the basis of form and
structure pseudopodia are of following four types
a) Filopodia- These are more
or less filamentous Pseudopodia tapering from base to the pointed tip, as in
Euglypha. It is composed of ectoplasm. Sometimes they may branch and form
simple or complex networks.
b) Lobopodia- These are lobe like Pseudopodia with
broad and rounded ends, as in Amoeba.
These are composed of both ectoplasm and endoplasm. Lobopodia move by pressure
flow mechanism.
c) Reticulopodia- The Reticulopodia are also filamentous.
Filaments are branched and interconnected profusely to form a network. This
type occurs in foraminiferans (e.g. Globigerina). Reticulopodia display two way
flow of cytoplasm.
d) Axopodia - These are more or less straight
pseudopodia radiating from the surface of the body. Each axopodia containing a
central axial rod which is covered by granular and adhesive cytoplasm. Like
Reticulopodia, axopodia also show two way flow of cytoplasm. Axopodia are
characteristic of heliozoans, such as Actinophrys.
2) Flagella:
Flagella
and their types: Flagella are extremely fine, delicate, highly vibratile
extensions of the protoplasm. It is the characteristics of all Mastigophora and
useful for locomotion. Following are types of flagella.
1.
Stichonematic:
It bears a single row of lateral mastigonemes. Ex. Euglena.
2.
Pantonematic:
The mastigonemes are arranged in two or more rows Ex. Monas.
3.
Acronematic:
The lateral mastigonemes are absent but the distal end bears a terminal
filament and hence appears like a whip hence the name whip flagellum. Ex. Polytoma.
4.
Pentachronematic:
It bears a terminal filament or mastigonemes in one or two rows. Ex. Paranema.
5.
Simple
or Ammonitic: Flagellum without mastigonemes and terminal filament Ex. Noctiluca.
3) Cilia.
Cilia, characteristic of Ciliata, resemble flagella in their
basic structure. These are vibratile small ectoplasmic processes. Electron
microscope reveals the presence of external membranous sheath, continuous with
plasma membrane of cell surface and enclosing the fluid matrix. Running along
the entire length of body of cilium are nine paired peripheral fibres and two
central fibres, all embedded in a structure less matrix. Central fibers are
enclosed within a delicate sheath. In between outer and inner fiber rings nine
spoke like radial lamella are present. In addition to these, one sub-fiber or
microfiber of each peripheral pair bears a double row of short projection,
called arms, all pointing in same direction.
Each cilium arises from a thickened structure, the basal
granule, basal body or blepharoplast. According to Henneguy–Lenhossek (1898), basal granules are centrioles or their derivatives.
Basal granule show nine peripheral sub fiber triplets, each disposed in a
twist-like fashion. In many species, cilia become fused variously forming
compound organelles, such as undulating membranes (Pleuronema),
membranelle (Vorticella), and cirri (Euplotes).
4) Pellicular contractile structures – Myonemes
In many Protozoa are found contractile structures, in
pellicle or ectoplasm, called Myonemes. These may be in the form of ridges and
grooves (e.g. Euglena), or
contractile myofibrils (e.g. larger ciliates), or microtubules (e.g. Trypanosoma).
They are extremely fine and highly contractile fibers located
in the pellicle (ectoplasm) of flagellate, ciliates and sporozoans etc. in more
complex form they may be extend up to endoplasm. They may be arranged
longitudinally, transversely or spirally. Myonemes are primarily organelles for
the metabolism e.g. Euglena, Paramecium and secondarily for locomotion
by muscle like contraction in Monocystis and Plasmodium.
Methods of Locomotion
Basically there are four known methods by which Protozoa
move- (1) Amoeboid movement, (2) Flagellar movement, (3) Ciliary movement, and
(4) Metabolic movement. Speed of locomotion varies from 0.2µ to 3µ per second
in amoeboid forms, 15µ to 300µ in flagellates, and 400µ to 2000µ in ciliates.
1) Amoeboid movement. It is characteristic
of all Sarcodina and certain Mastigophora and Sporozoa. It consists of formation of
pseudopodia by the streaming flow of cytoplasm in the direction of movement.
Locomotion by pseudopodia is possible only over the surface precisely about the
mechanism involved in the formation of pseudopodia, but the most convincing
theory at present is that it depends upon active contraction of the ectoplasmic
tube (plasmagel) at the posterior end of the body. This lead the endoplasm
(plasmasol) to flow forward into expanding pseudopodium. This process involves
continuous solation at the posterior end and gelation at the anterior end. This
is called sol-gel or change of viscosity theory.
2) Flagellar movement. It is characteristic of Mastigophora which bear one or more
flagella. The flagella need liquid medium for movement or locomotion. Three
types of flagellar movement have been recognized:
a) Paddle stroke. The movement of a flagellum is sideways lash, consisting of
an effective down stroke with flagellum held out rigidly and a relaxed recovery
stroke in which flagellum, strongly curved, is brought forward again. As a
result, the animal moves forward, gyrates and is also caused to rotate on its
longitudinal axis.
b) Undulating motion. Wave-like undulations in flagellum, when proceed from tip to
base, pull the animal forward. Backward movement is caused when undulation pass
from base to tip. When such undulations are
spiral, they cause the organism to rotate in opposite direction.
c) Simple conical
gyration. Butschli’s screw theory postulates
a spiral turning of flagellum like a screw. This exerts propelling action,
pulling the animal forward through water with a spiral rotation as well as
gyration (revolving in circles) around the axis of movement.
3) Ciliary movement. Most ciliates appear to move in a spiral path, rotating on
their axis as they go. Spiral movement is due to in opposite directions on the
two sides of the pseudopodial filaments; oblique strokes of all body cilia
working together and striking in the same direction. Cilia also need liquid
medium for their movements. Large ciliates are the swiftest swimmers, and the
champion of them may be named Paramecium
caudatum.
4) Metabolic movements. This type of typical movement occurred in certain
flagellates (e.g. Euglena) and most
sporozoans at certain stages of their life cycles. Such organisms are seen to
show gliding or wriggling or peristaltic movement. Contractile myonemes or
microtubules, present in their pellicular walls, are responsible for this type
of movement. Movements of this kind are usually also referred to as gregarine
movements since they are characteristically exhibited by most gregarines (relating
to a group of microscopic worm-like protozoans that are internal parasites of
insects, annelids, and other invertebrates).
Question Bank
Q. 1 A) Multiple Choice
Questions (01 Mark each)
1) The
term protista was coined by ----------.
a) John Hogg b) Ernst Haeckel c)Ernst
Hogg d) Robert hook
2) Plant-like
protists (algae) have-------.
a) chlorophyll b)
melanin c)mitochondria d) none
3) It contains of
species of one-celled algae called ------- which means 'spinning swimmers'.
a) tinoflagellate b) monoflagellate
c) dinoflagellate d) pinoflagellate
4) Protists that
have resemblance to animals are known as --------.
a) flagellates b) ciliates c)protozoans
d) none of these
5) Pseudopodia are temporary structures form by
the streaming flow of cytoplasm.
a)cytoplasm b)
nucleoplasm c)orgenelles d) nucleus
6)
On the basis of form and structure pseudopodia are of four
types.
a) one b) two c)three d) four
7) Lobopodia are ----- like Pseudopodia with broad and
rounded ends.
a) filamentous b) straight c) lobe d) crossed
8) In many Protozoa are found contractile
structures, in pellicle or ectoplasm, called--------.
a) myonemes b) tyonemes c) dyonemes d)
nyonemes
9) Cilia also need ---- medium for their
movements.
a) solid b) liquid c)semisolid
d) gaseous
10) ------- and Volvax
having chlorophyll, which are considered animal by zoologists and plants
(algae) by botanists.
a) Euglena b)
Opalina c) Paramoceium
d) Plasmodium
Q. 1 B)
Answer in one sentence (01 Mark each)
1) Who observed first
Protista?
2) Which protists have
chlorophyll?
3) Write the example of
fungus like protists?
4) Write the methods by
which protozoan move.
5) Which structure is formed
during amoeboid movement?
6) By which structure
flagellar movement is carried out in protozoans?
7) By which structure
ciliary movement is carried out in protozoans?
8) By which structure
metabolic movement is carried out in protozoans?
Q. 2 Define / Explain / Comment (2 Marks Each)
1) Protist 2)
Protozoans 3)
Amoeboid movement
4) Flagellar movement 5) Ciliary movement 6) Metabolic movement
7) Falgella 8) Cilia 9) Pseudopodia
Q. 3
Answer the following (03 Marks each)
1) Describe the Amoeboid movement of
protozoans?
2) Describe the falgellar movement of
protozoans?
3) Describe the ciliary movement of
protozoans?
4) Describe the metabolic movement of
protozoans?
5) With neat and well labeled diagram
describe Amoeba.
6) With neat and well labeled diagram
describe Euglena
7) With neat and well labeled diagram
describe P. vivax.
8) With neat and well labeled diagram
describe Paramecium.
9) Explain the fungus like protest.
Q. 4
Answer the following (04 Marks each)
1) Describe the locomotary organ pseudopodia.
2) Describe the locomotary organ falgella
3) Describe the locomotary organ cilia.
4) Describe the locomotary organ myonemes.
5) Write a short note on plant like protists.
6) Write general characteristics of Protista.
Q. 5
Describe in detail (06 Marks each)
1) Explain the locomotary organelles in protozoa.
2) Explain the locomotary method of protozoans.
3) Classify the phylum protozoa up to classes giving their diagnostic characters and familiar examples
lll
Unit 2Phylum Porifera
General characteristics and
Classification Up to Classes,
Canal System in Sycon.
Porifera
Poriferans are commonly referred to as sponges. An
early branching event in the history of animals separated the sponges from
other metazoans. As one would expect based on their phylogenetic position,
fossil sponges are among the oldest known animal fossils, dating from
the Late Precambrian. Since then, sponges have been conspicuous members of
many fossil communities; the number of described fossil genera exceeds 900. The
approximately 5,000 living sponge species are classified in the phylum
Porifera, which is composed of three distinct groups,
the Hexactinellida (glass sponges), the Demospongia, and the Calcarea (calcareous
sponges).
General
characteristics of Phylum Porifera
1.
Kingdom: Animalia
2.
Sponges
were studied extensively by Grant in 1836 and gave the name Porifera. The
classification of sponges is based almost entirely on microscopic skeletal structures.
Such divisions are not unanimous particularly in the case of horny and
siliceous sponges.
3.
The
Phylum Porifera consists of 10,000 species of which 50 are fresh water ones.
The classification followed in this text is based on the classificatory plan
outlined by Ruppert and Barnes, 1994.
4.
Habitat: Porifera
are all aquatic, sessile and sedentary, few grow like plant, majorities are
marine but few in fresh water. Sponges are found all over the world and at all
depths of the ocean. However, most sponges prefer relatively shallow water, but
some groups (glass sponges) prefer deeper waters. Poriferans present a great
variety of external forms.
5.
Habit: Sponges
occurring singly or in groups. They
are solitary or colonial.
6.
Grade
of organization: cellular
grade of body. They
possess cellular level of organization i.e. they are loose aggregation of cells
without forming tissues. Tissue organization very much restricted and lacking
organs and co-ordination between cells.
7.
Shape: Body shape is variable, mostly cylinder
shaped. The body
shape varies considerably. For ex. Vase like or cylindrical or flat, globular
or irregular branching masses. They may be saucer-shaped, cup-shaped, tubular,
rod-shaped, foliaceous, trumpet-shaped, fan-shaped, mushroom-shaped, lobed,
branched, irregular etc. The forms are even variable in the same species and is
therefore of little use in identification. Adult sponges are usually sessile;
the motile phase is the larva produced through sexual reproduction.
8.
Their
colour varies greatly ie. Grey or dull-brown, bright yellow, red or orange
other have delicate shades of violet or pink still others are black or white.
Some sponges are green due to the presence of symbiotic algae.
9.
Symmetry: Asymmetrical or radially symmetrical.
10. Germ layer: Body wall is diploblastic which consists of an outer layer, dermal layer,
called Pinacoderm and an inner layer called Choanoderm and characteristic
flagellated cells called choanocytes, lines the inner side of the body wall and
are related with water circulation and feeding. In between these two layers,
there is a gelatinous and non-cellular mesoglea containing numerous free
amoeboid cells.
11. Coelom: Absent; acoelomate but spongocoel is present
12. Surface of the body has numerous perforation
called ostia (for the entry of water) and a large pore at the apex called
osculum (for the exit of water). Absence of a true body cavity or gut.
13. Water canal system: The lack of any
conspicuous movement of body parts of the sponges, Aristotle, Pliny and other
ancient naturalists said that sponges were plants. It was much later, in 1765,
when internal water currents were first observed, that the animal nature of the
sponges was established. The
unique features of sponges are a system of pores, canals and chambers for
passage of water current. Through which water current flows and transporting
food and oxygen takes place.
14. Endoskeleton: Either calcareous spicules (calcium
carbonate) or siliceous spicules (silica) or sponging fibers (protein).
15. Nutrition: Exclusively filter feeder, holozoic
16. Digestion: Intracellular
17. Respiration: Gas exchange by diffusion.
18. Nervous system: Nervous
and sensory cells are absent.
19. Circulatory system: absent
20. Reproduction: Reproduction
occurs both asexually and sexually. Asexual reproduction takes place by
building, fission or gemmule formation. Sexual reproduction by producing sperms
and ova. The ova and sperms develop from the archaeocytes.
21. All sponges are hermaphrodite but
cross Fertilization takes place. Cleavage is holoblastic, development is
indirect followed by a free swimming ciliated larva called amphiblastula.
Development indirect through free swimming, ciliated, planktonic larvae.
Classification of Phylum Porifera
Based on the type of skeleton system the phylum Porifera
is divided into three classes
§ Class 1: Calcarea or Calcispongiae
§ Class 2: Hexactinellida or Hyalospongiae.
§ Class 3: Demospongiae
§ Class 4:
Sclerospongiae
Class
1: Calcarea or Calcispongiae
(calcarius: lime / calcium)
§ Habitat: Exclusively marine; shallow coastal water species.
§ Habit: Solitary or colonial nature.
§ Endoskeleton: calcareous spicules composed of
calcium carbonate
§ Symmetry: Radially symmetrical
§ Shape: Cylindrical shape
§ Osculum narrow and provided with oscular
fringe.
§ Examples: Sycon, Leucosolenia Fig. 13 Sycon gelatinosum
Class
2: Hexactinellida or hyalospongiae:
(Hex: six, actin: ray, idea: terminal)
§ Habitat: Exclusively marine (deep sea); chiefly occurs in deep- water habitats, They
have a worldwide distribution but are mainly restricted to deeper waters (200
to > 6000 m).
§ Habit: Solitary in nature.
§ Endoskeleton: six- rayed siliceous spicules or
triaxon siliceous spicules often fused into vase-shaped structures.
§ Symmetry: Radially symmetrical
§ Shape: Cylindrical shape.
§ Pinacocytes absent,
instead the epidermis forms a net-like syncytium formed from interconnecting
pseudopodia of amoebocytes.
§ Choanocytes are
restricted to finger-like simple or folded chambers.
§ The spongocoel opens by
a wide osculum.
§ Examples: Euplectella, Hyalonemma
Class
3: Demospongiae
(Demos:
frame)
§Habitat:
Mostly marine and some are freshwater poriferans; and is the largest class
containing over 90% of the total sponge species.
§Endoskeleton:
Siliceous spicules or sponging fibres or both or none.
§The
spicules are monaxon or tetraxon but never six-rayed.
§Symmetry:
asymmetrical.
§Shape:
Irregular
§Canal
system complicated.
§Spongocoel
is totally absent.
§Choanocytes
form very small, round type of flagellated chambers.
§Examples: Spongilla (fresh water
sponge), Euspongia (bath sponge)
Class 4: Sclerospongiae:
i. Marine, exhibits cryptic habits and prefer
caves.
ii. Skeleton contains
spicules of silica and aragonitic calcite as well as spongin.
iii. Spicules, Spongin
fibers and the surrounding living tissues rest on a solid basal skeleton of
calcium carbonate or are enclosed within calcium carbonate chambers.
Examples:
Acanthochaetetes, Astrosclera, Stromatospongia.
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Canal system in sycon
Sycon is a sedentary sponge. It leads an
aquatic life. The body of sycon shows pores and canals which form a
complex canal system. It is called sycon type of canal system. It is useful to
draw water current inside the body. These water currents bring in food and
oxygen. The body wall of sycon contains outer dermal layer and
inner choanoderm. In between
these two layers mesenchyme
is present. The body wall is folded regularly
and develops a regular canal system.
1) Ostia: The body wall is folded. In between two
folds an incurrent canal is present. The opening of incurrent canal shows a
pore membrane. This will show one or two ostia, through which water enters into
the incurrent canals. The ostium is surrounded by myocytes. These amoebocytes
will work as sphincters. They can close these openings or open them to regulate
the inflow of water.
2) In current canals: In between two folds of the body wall
an incurrent canal is present. These canals end blindly towards inside. This is
lined inside by pinacocytes. These are flat cells and are contractile.
3) Prosopyles: The incurrent canal opens into the
radial canal through prosopyles'.
4) Radial canals: In between two incurrent canals a
radial canal is present. It ends blindly to the exterior. It leads into
excurrent canal internally.
Radial
canal is lined with choanocytes or flagellated cells. Hence, these chambers are
called flagellated chambers.
5) Apopyle: Radial canal opens into excurrent canal
through an opening called apopyle. The apopyle is also surrounded by Myocytes.
6) Excurrent canal: It is short and wide chamber. It opens
into spongocoel. This canal is lined with flat epithelial cell like the
spongocoel. The broad opening between excurrent canal and sponogocoel is also called
internal ostium.
7) Spongocoel: The central part of the cylinder of
sycon will show a hollow cavity called spongocoel. It is lined with epithelial
cells. At the apex it opens out through osculum.
Because
of the action of flagella of choanocytes water is drawn into the body. This is
called incurrent water. This brings in food and oxygen. Hence, it is called
nutritive current. The water that goes out of the osculum is called excurrent
water.
e.g.
Sycon. The course of water current is
ostia incurrent canal prosopyles radial canal apopyles spongocoel
osculum.
Functions of Sponge
Canal System:
1) It brings constant supply of water into the body
and helps in respiration.
2) Water
brings with in small food particles which are used by the sponge
3) It helps in the process of reproduction.
4) It
helps in the process of discarding waste matter out of the body.
Question Bank
Q. 1 A) Multiple Choice Questions (01 Mark each)
1) Sponges
are ----------.
a) coelomate b) acoelomate c)pseudocoelomate
d) none of these
2) In sponges inner
body wall is called as---------.
a) endoderm b) pinacoderm c)
chaoanoderm d) none of these
3) Cells of
sponges are called as------
a) choanocytes b)
pinocytes c) pseudocytes d) none of these
4) Sponges possess
cellular level of organization.
a) cellular b)
tissue c) organ d) system
5) On body surface
sponges have numerous pores for the entry of water called--------.
a) ostica b) osculum c)
ostia d) osculica
6) A large pore at the apex of sponges for the
exit of water called--------.
a) ostica b) osculum c)
ostia d) osculica
7) Body cavity of
sponges is-------
a) coelom b) pseudocoelom c)
spongocoel d) lumen
8) Spiculesand
sponging fibers forms ------ in sponges.
a) endoskeleton b)
exoskeleton c) skeleton d) none
Q. 1 B) Answer in one sentence (01 Mark each)
1) How many germ layers present in Porifers?
2) What are ostia?
3) What is osculum?
4) What is water canal system?
5) What is spongocoel?
6) What form the endoskeleton of sponges?
7) Which type of canal system is present in sycon?
8) Write the course of water current in sycon type
of canal system.
Q. 2 Define / Explain / Comment (2 Marks Each)
1) Spongocoel 2) Canal system 3)
Ostia 4) Osculum
Q. 3 Answer the following (03 Marks each)
1) Write the functions of canal system.
2) Write the characteristics of class Calcarea.
3) With neat and well labeled diagram
describe the Hylonemma.
4) With neat and well labeled diagram
describe Sycon.
5) With neat and well labeled diagram
describe Euspongia (bath sponge).
6) Draw well labeled diagram of sycon
canal system.
Q. 4 Answer the following (04 Marks each)
1) Write general
characteristics of phylum Porifera
2) Write the characteristics of class Hexactinellida.
3) Write the characteristics of class Demospongiae.
Q. 5 Describe in detail (06 Marks each)
1) Describe the canal system in sycon.
2) Classify the phylum porifera up to classes giving their diagnostic characters and familiar examples.
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