NEET Biology Animal Kingdom Notes - Phylum-Porifera

 

Phylum-Porifera

 

Phylum Porifera.

 

(i) Introduction : Lowest multicellular animals or metazoans without true tissues, i.e., at ?Cellular level? of body organization. Familiar as sponges, these animals are well-known for their ability to absorb and withhold fluids. The word ?Porifera? means pore bearers (Gr., porus = pore; ferre = to bear); Their body wall has numerous minute pores, called ostia, through which a continuous current of outside water is drawn into the body. About 5,000 species are known.

(ii) Brief History : Robert Grant (1825) finally proved that sponges are animals, and coined the name ?Porifera? for these. Schulze (1878), Butschli (1884), Sollas (1884) and Delage (1898) separated sponges from other metazoans on basis of embryological studies, and suggested a separate group, ?Parazoa? for these.

          (iii) Salient features : Phylum porifera has the following salient features :

(1) All the sponges are Aquatic, Sedentary, Asymmetrical or Radially, First multicellular organisms and have cellular grade of organization.

(2) They are diploblastic. Ectoderm is formed by pinachocyte and endoderm is formed by choanocyte. Both layers are called pinachoderm and choandoderm.

            (3) The body is perforated by numerous minute pores called ostia.

            (4) The ostia open into a large cavity called spongocoel.

            (5) The spongocoel opens to the outside by a large opening called osculum.

            (6) The sponges possess an endoskeleton in the form of calcareous spicules.

            (7) Excretion and respiration occur by diffusion.

            (8) They have greater power of regeneration.

            (9) Reproduction takes place by asexual or sexual methods.

            (10) Development is indirect or direct. The common larval are parenchymula, amphiblastula, etc.

          (a) Class 1. Calcarea

            (1) Skeleton is formed of Calcareous spicules. 

            (2) Radially symmetrical.

            (3) Choanocyte cells are large and conspicuous

            Examples : Clathrina, Leucosolenia, Sycon, etc.,

            q  Euplectela is the sponge which is given as a Gift in Japan.

            q  Leucosolenia is a smallest sponge.

q  Ectorderm is formed by pinachocyte and endoderm is formed by choanocyte. Both layer is called pinachoderm and choanoderm.

            (b) Class 2. Hexactinellida

            (1) Skeleton is formed of six rayed triaxon, silicious spicules,

            (2) Canal system is branched or unbranched.

            (3) Radially symmetrical.

            (4) These are also known as glass sponges.

            Examples : Pheronema, Hyalonema, etc.,

            q Hylonema is a Glass rope sponge.

 

          (c) Class 3. Demospongia

(1) Skeleton either absent or present. When present it is either formed of spongin fibres or combination of spongin fibres and silicious spicules.

            (2) The silicious spicules when present are never six rayed

            (3) The canal system is complicated Rhagon type

            (4) These sponges are of great economic importance

Examples : Cliona, Spongilla, Chalina, Euspongia, Hippospongia, Oscarella, etc.,

            q Spongilla is a fresh water sponge.

 

 

 Phylum Protozoa.

 

(i) Introduction: All unicellular (or acellular) eukaryotic animals: Most primitive (Gr. Porots = first + zoon = animal) organisms considered animals because of heterotrophic nutrition and motility. Although the whole body is a single minute cell. About 50,000 species (30,000 present and 20,000 extinct) are so far known.

(ii) Brief History: Protozoans were first studied by Leeuwenhoek (1677). The name ?Protozoa? was coined by Goldfuss (1817). The branch of their study is called Protozoology.

          (iii) Salient Features

            (1) Protozoans are the simple and primitive organisms

            (2) They are free living or parasitic

            (3) All the free living forms are aquatic

(4) They are asymmetrical or radially symmetrical or bilaterally symmetrical

            (5) They are unicellular (acellular)

            (6) They have protoplasmic grade of organization.

(7) Locomotion is effected by flagella, cilia or pseudopodia.

(8) Nutrition is holophytic, holozoic, saprozoic or parasitic.

            (9) Digestion is intracellular

            (10) Excretion & Respiration occurs by diffusion

(11) In fresh water protozoans osmoregulation is carried out by the contractile vacuoles.

            (12) Encystment is a common phenomenon

            (13) Reproduction occurs by asexual and sexual methods.

          (iv) Classification of Protozoa

            (a) Class 1. Flagellata or Mastigophora

            (1) The body is covered by a thin pellicle or cuticle.

            (2) The locomotory organs are flagella.

            (3) The contractile vacuoles are present in fresh water forms with accessory vacuoles.

            (4) Chloroplast are found in some forms.

            (5) They may be free living or parasitic.

The class flagellata has been divided into eight orders. They are as Chrysomonadina, Cryptomonadina, Euglenoidea,  Phytomonadina, Dinoflagellata, Cystoflagellata, Protomonadina and Polymastigina

Examples : Chrysamoeba, Cryptomonas, Euglena, Volvox, Chlamydomonas, Noctiluca, Mastigamoeba, Monal, Bado, Trypanosoma, Leishmania, Proterospongia etc.,

            q Euglena is a connecting link between Animal & Plant.

            q  Trychonymph (symbiotic) live in alimentary canal of termite that is digest to cellulose.

          (b) Class 2. Rhizopoda

            (1) There is no definite cell wall or pellicle

            (2) There is no definite shape

            (3) The locomotory organs are pseudopodia

            (4) There is no permanent mouth or anus.

            (5) The contractile vacuoles are present in the fresh water forms.

The rhizopoda has been divided into five orders. They are as Lobosa, Filosa, Foraminifera, Heliozoa and Radiolaria.

            Examples : Amoeba, E..histolytica, E.coli etc.,

          (c) Class 3. Ciliophora

            (1) The body is covered by thin pellicle

            (2) They have a fixed permanent shape

            (3) The locomotory organs are cilia

            (4) Tentacles are present

            The class ciliophora is divided into two sub-classes, namely Ciliata and Suctoria.

            Sub-class 1. Ciliata.

            (1) Cilia are present throughout life.

            (2) Tentacles are absent

            (3) Mouth and cytopharynx are usually present. Cytopyge is a temporary anal aperture.

            (4) Contractile vacuoles are present.

            (5) Trichocysts, organs of offense and defence are present in certain forms.

            Examples : Paramecium, Stylonchia Vorticella, etc., Paramecium is filter feeder

            q  In a paramecium two contractile vacuole present. Posterior contractile vacuole is highly active.

            Sub-class 2. Suctoria

            (1) Cilia are present only in the young conditions and adults are devoid of them.

            (2) Tentacles are present in the adult

            (3) One to many contractile vaculoes are present

            Examples: Acineta, Dendrocometes, Dendrosoma, etc.,

            (d) Class 4. Sporozoa

            (1) They are exclusively endoparasitic

            (2) The body is covered by pellicle.

            (3) Reproducion takes place by spore formation

            The class is divided into two sub-classes, namely, Telosporidia and Neosporidia

            Sub-class 1. Telosporidia

            (1) The spores do not contain polar capsules or filaments

            (2) The life history ends with the formation of spores.

            (3) The spore cases are simple and contain many spores

            Examples : Monocystis, Gregarina, Isopora, Eimeria, Plasmodium, Babesia, etc.,

            Sub class 2. Neosporidia

            (1) The trophozoite is amoeboid multinucleated

            (2) Spore cases are complex usually having a single germ

            Examples : Nosema, Myxidium, Globidium, etc.,