Animal Kingdom Part 1

(General Account of Animals and Phylum Protozoa)

The Animal Kingdom has been divided into two sub kingdoms:-

1. Protozoa: It includes unicellular eukaryotic animals with a single Phylum called protozoa. e.g. Euglena, Amoeba, Paramecium                   etc.

2. Metazoa : It includes multicellular animals. e.g. Porifera, Coelenterata to Chordata. The Metazoa is further divided into two branches,namely Parazoa and Eumetazoa.

Parazoa : It includes Porifera/sponges in which cells are loosely aggregated and do not form true tissues or organs

Eumetazoa : It includes truely multicellular organisms with organ and organ system level of organization. e.g. Coelenterata to Chordata.

Symmetry:-

Based on symmetry Eumetazoa is further divided into Radiata and Bilateria.

Radiata : It includes radially symmetrical animals. In radial symmetry, the animal can be divided into two identical halves on by any of the radial planes along anterior posterior axis of the body. e.g.

Coelenterata and Ctenophora

Bilateria : It includes bilaterally symmetrical animals. In bilateral symmetry, the animal can be divided into two identical halve only by a single plane passing from dorsal side to ventral side and along the anterior posterior body axis. The animal can be divided only into two

identical left and right parts. e.g. Platyhelminthes to Chordata.

Source: http://www.millerandlevine.com/ques/images/symmetry

Germ Layers:-

All the body tissues of the adult animal are formed from germ layers.

Depending upon no. of germ layers, animals are classified into

1. Diploblastic: Two germ layers. Outer ectoderm and inner endoderms with a non cellular mesoglea in between the two. eg. Coelenterata

2. Triplobastic:- Three germ layers. Outer ectoderm, middle mesoderm and inner endoderm. eg. Platyhelminthes to Chordata

Body Cavity (Coelom):-

Depending upon presence or absence of body cavity Bilateria are divided into 3 categories

1. Acoelomata : In these animals, coelom (body cavity lying between the gut and the body wall) is absent. e.g. Platyhelminthes

Source: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBook%20Diversity_7.html

2. Pseudocoelomata : In these animals, a false coelom (body cavity not lined with coelomic epithelium) is present. e.g. Aschelminthes

/Nematoda.

Source: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBook%20Diversity_7.html

3. Eucoelomata: In this group, a true coelom (body cavity lined with coelomic epithelium) is present. e.g. Annelida to chordata.

Source: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBook%20Diversity_7.html

The coelom in eucoelomata is of two types:-

1. Schizocoelomata: Coelom develops by splitting up of mesoderm. eg.

Annelida, Arthropoda, Mollusca

2. Enterocoelous coelomata : Coelom is enterocoel which originates by fusion of pouches of embryonic gut (archenteron)

The coelomates are two types-

1. Protostomes: In these animals, the embryonic blastopore develops into mouth eg. annelida mollusca, arthropoda.
2. Deuterostomes: In these animals the embryonic blastopore develops into anus eg. echinoderms, hemichordates, and chordates

Body Plan:-

There are three types of body plans in animals

i. Cell aggregate: eg. Sponges

ii Blind sac: In this body plan, the alimentary canal has only one opening eg. Coelenterates, Platyhelminthes

iii.Tube within tube: Alimentary canal has two openings eg.Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata

Blood vascular system:-

Open type:- It does not have blood capillaries. Therefore, blood comes

in direct contact of tissues. eg. most Arthropods,, some Molluscs and Tunicates.

Closed type:- It has blood capillaries. Therefore, blood does not come in direct contact of tissues.eg. Many Invertebrates and all Vertebrates

Notochord:-

Notochord is a rod like mesodermal structure present on the dorsal side of some animals. Such animals are called Chordates eg. Fishes, Amphibians, Reptiles, Birds, Mammals. The animals which do not have a notochord are called Non-chordates/invertebrates.

Non Chordata/Invertebrates:-

The animals which do not have a notochord are called invertebrates.

e.g. sponges. Invertebrates are characterised by the following salient features –

1. Absence of vertebral column.
2. Nerve cord is solid in nature.
3. Nerve cord is present on the ventral side and never on the dorsal side.

The invertebrates are grouped into about 30 phyla which are of two types, namely major phyla and minor phyla.

(a)Major Phyla :

1. Protozoa
2. Porifera
3. Coelenterata
4. Platyhelminthes
5. Aschelminthes
6. Annelida
7. Arthropoda
8. Mollusca, and
9. Echinodermata.

(b)Minor Phyla :

1. Mesozoa (2) Nemertinea (3) Endoprocta (4) Acanthocephala (5) Rotifera (6) Gastrotricha (7) Kinorhyncha (8) Nematomorpha (9) Ectoprocta (10) Brachiopods (11) Phoronida (12) Chaetognatha (13) Priapulida (14) Sipunculida (15) Echiuroidea (16) Pogonophora etc. Only major phyla are in the syllabus and will be discussed one by one separately.

Phylum Protozoa

This phylum includes all unicellular/acellular eukaryotes : (Gr. Porots = first + zoon = animal). A single cell performs all the vital life activities of life. About 50,000 species are so far known.

Genearl Characters:-

1. They are simple and primitive organisms, free living or parasitic, asymmetrical or radially symmetrical or bilaterally symmetrical organisms.
2. They have protoplasmic level of body organization.
3. Locomotion is by flagella, cilia or pseudopodia.
4. Nutrition is holophytic, holozoic, saprozoic or parasitic. But mostly

heterotrophic in nutrition.

5. Digestion is intracellular
6. Excretion & Respiration by diffusion through general body surface.

(7)Osmoregulation (water and salt balance) by contractile vacuoles in fresh water protozoans. Contractile vacoule is absent in parasitic and marine forms.

8. Reproduction occurs both by asexual and sexual methods.

Classification:-

Class 1. Flagellata or Mastigophora

1. Body covered by a thin pellicle or cuticle.
2. Locomotion by flagella.

(4) Some forms have chloroplast.

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

Euglena is a connecting link between Plants and animals. Trychonympha lives symbiotically in the alimentary canal of termites to digest cellulose for the termite.

Class 2. Sarcodina/Rhizopoda

(1) Without definite shape, cell wall or pellicle. (2)Locomotion by pseudopodia

(3) No permanent mouth or anus.

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

Structure of Amoeba

Source: http://schoolnet.gov.mt/biology/Amoeba.

Class 3. Cilliata/Ciliophora

1. Body covered by a thin pellicle with a fixed permanent shape
2. The locomotion by cilia. Mouth and cytopharynx are usually present. Cytopyge is a temporary anal aperture.
3. Trichocysts for offense and defence are present in certain forms. Examples :Paramecium.

Paramecium has two contractile vacuoles. Posterior contractile vacuole is highly active.

Class 4. Sporozoa

1. All exclusively endoparasitic
2. Body covered by pellicle.
3. Reproducion by spore formation The class is divided into two sub-

classes, namely, Telosporidia and Neosporidia    Examples : Monocystis, Plasmodium, Babesia, etc.,

Plasmodium-the malarial parasite:-

Plasmodium vivax, a malarial parasite, is an intracellular blood parasite that can affect humans and other vertebrates. Plasmodium vivax is an endoparasite and is well-adapted to the parasitic mode of life. The life cycle of Plasmodium vivax is complicated and is completed in two different types of hosts: definitive and intermediate.

Definitive and Intermediate Hosts

A definitive host provides nutrition to the parasite. Humans beings act as definitive hosts where the asexual cycle occurs. The asexual cycle (multiplication) of Plasmodium in man is known as schizogony .

Schizogony takes place in liver and RBCs of man.

An intermediate host helps in transmission from one definitive host to the other. Mosquitoes (only female Anopheles) are the intermediate hosts where the sexual cycle occurs. Sexual cycle involves gametogony and sporogony

The life cycle of Plasmodium vivax is divided into the following stages.

Pre-Erythrocytic Cycle

When an infected female Anopheles mosquito bites a healthy person to feed on his blood, numerous sporozoites enter into the blood stream of the person along with the saliva of the mosquito. Sporozoite is the infective stage

Pre-erythrocytic schizogony happens when the sporozoites first go to the parenchyma cells of the liver and remain within it for about one week. During this period, each sporozoite develops into a schizont. The schizonts undergo multiple fission to form a large no. of merozoites.

The merozoits of the first generation are called cryptozoites. The cryptozoites enter                          fresh liver cells, form schizont which will divide to form merozoites. These merozoites of second generation are called metacryptomerozoites. This phase is known as pre-erythrocytic cycle which takes place in liver cells.

Erythrocytic Cycle

This cycle is divided into the following stages:

Trophozoite Stage—

After entering the blood stream, merozoites start invading the red blood cells (RBC). Now, the parasite in RBCs is known as trophozoite. The trophozoite is the adult stage of the parasite.

Signet Ring Stage--

A non-contractile vacuole appears in its cytoplasm and grows by feeding the haemoglobin of the RBC. The nucleus is pushed on one side and parasite assumes a ring-like appearance.

Amoeboid Stage--

The vacuole disappears and the parasite assumes an amoeboid form to represent this stage.

Schizont Stage--

By thrusting its pseudopodia inside the cytoplasm of RBC, it feeds on the hemoglobin and increases its size and forms the schizont.

Merozoite Stage--

The schizont undergoes asexual multiplication. The nucleus of schizont divides to form eight to 24 daughter individuals and forms merozoites which are released by rupture of RBC. These merozoites enter fresh RBCs to repeat the cycle every 48 hours and form a large no. of merozoites. The toxins are also released by rupture of RBCs and the accumulation of toxins causes Benign tertian malaria.

Post or Exo-Erythrocytic Cycle

The merozoites from blood may go to liver cells and they may continue to produce about 1,000 exo-erythrocytic merozoites within the liver without any symptom, and may live there for some years. After this dormant stage, they may again become infectious. These merozoites invade either fresh parenchyma cells or RBCs.

Sexual Cycle

After several generations of multiplication, some merozoites form gametocytes in the RBC. The female Anopheles mosquito takes a blood meal from the infected person and thus ingests both sexual(gametocytes) and asexual forms. In the mosquito, the asexual forms soon get digested and the sexual forms survive and develop. The sexual cycle is divided in the following stages:

Gametogony, where some of the schizonts are modified for sexual reproduction and the resulting merozoites, after entering the RBC, do not form trophozoites but grow slowly and specialize themselves as gamonts or gametocytes. Remember, the gametocytes are produced in man. There are two forms of fully-grown gametocytes--female, or macrogametocyte, and male, or microgametocyte which form female gamete and male gamete in mosquito respectively.

Fertilization:

The actively moving male gamete(microgamete) is attracted by the female gamete(megagamete) and unites to form a zygote.

Sporogony:

The actively moving zygote moves vibrantly inside the mid-gut, bores through the wall of the gut wall and comes to rest under epithelium and the outer wall of the stomach. The zygotes that fail to get shelter in the stomach wall of the mosquito develop into Ookinete. Ookinete secrete a thin membranous cyst wall; this is known as Oocyst. The nucleus divides repeatedly and ultimately a large number of sickle- shaped sporozoites are formed from a single Oocyst. The Oocyst ruptures about 10 days from its formation and sporozoites are liberated in the hemocoele of mosquito; later they migrate to the salivary gland and the female Anopheles becomes infected, enabling her to inoculate the parasite into the blood stream of healthy persons.

Types of malaria:-

P. vivax is the most extensively distributed and causes much debilitating disease. P. falciparum, which is also widely spread, results in the most severe infections and is responsible for nearly all malaria- related deaths. P. ovale which is mainly confined to Africa is less prevalent, while P. malariae, which causes the least severe but most persistent infections, also occurs widely.

Practice Test Paper

1. A coelom (body cavity) derived from blastocoel is known as
   1. Enterocoel (b) Schizocoel (c) Haemocoel (d) Pseudocoelom
2. When only single opening is present in the alimentary canal, then the body plan is
   1. Open (b) Blind sac (c) Cell aggregate (d) Tube in tube

3. Which one of the following is the connecting link between chordata and non-chordata
   1. Tachyglossus (b) Amphioxus (c) Balanglossus (d) Sphenodon
4. Which phylum belongs to Duterostomia
   1. Echinodermata (b) Mollusca (c) Arthropoda (d) Annelida

5. In protozoa contractile vacuole is generally absent in the class
   1. Rhizopoda (b) Sporozoa (c) Ciliata (d) Flagellata
6. Which is not the locomotory organ of protozoa
   1. Cilia (b) Flagella (c) Pseudopodia (d) Parapodia

7. Which protozoan is unlikely to have a contractile vacuole
   1. Euglena (b) Paramecium (c) Amoeba (d) Plasmodium

8. Class sporozoa of phylum protozoa is characterised by
   1. Flagella (b) Cilia (c) Parasitism (d) None of these

9. Pseudopodia is a characteristic feature of which class
   1. Mastigophora (b) Sarcodina (c) Sporozoa (d) Ciliata

10. Euglena belongs to
    1. Flagellata (b) Ciliata (c) Sporozoa (d) None of these

11. The unicellular eukaryotes are placed in the phylum……
12. The cell aggregate body plan is found in……….
13. The type of symmetry found in the Ctenophores is ……..
14. Name the phylum in which the body cavity is pseudocoel and represents a persistant Blastocoel
15. The level of organization found in Protozoa is
16. The type of body plan found in porifera is…..

17. Enlist the function of contractile vacuole in Protozoa. Do all Protozoans have contractile vacuoles
18. What is open type of blood vascular system
19. Differentiate between radiata and bilateria
20. Differentiate between Blind sac and tube within tube body plan

Answers and Solutions

1. d
2. b
3. c
4. a
5. b
6. d.   Parapodia are found in Annelida
7. d.   Plasmodium is parasitic, Therefore, does not have contractile vacuole
8. c
9. b
10. a
11. Protozoa
12. Porifera
13. Radial symmetry
14. Nematoda
15. Protoplasmic level of organization
16. Cell aggregate