Multicellular organisms are called animals. They may be acellular also. Multicellular animals are heterotrophs. About ten million species of living animals are known. These species are different from each other in shape, size, structure and ways of living. All animals except porifers are motile and are provided with sensory or nervous sytem.
Body Organisation of Animals
Body organisation of animals is divided and studied as follows :
1. Body plan : There are three basic plans of the body structure :
(a) Cell aggregate plan : Animal cells are loosely arranged in groups. The organ system is absent. e.g. porifers.
(b) The blind sac plan : The blind sac plan is more evolved plan than the cell aggregate plan. The alimentary canal opens outside and has only single opening. Both ingestion and egestion are done through this opening only. Division of labour is developed. This type of digestive tube is termed as blind sac. e.g. coelenterates and flatworms.
(c) The tube within a tube plan : Digestive system has a mouth and anal opening. Ingestion is by mouth and egestion is by anus. This plan is more evolved and have complex form.
2. Symmetry : Symmetry is of three types, namely:
(a) Asymmetrical : In asymmetrical body an animal cannot be divided into two equal and similar halves from any point e.g. snail.
(b) Bilateral symmetry : In this symmetry when an animal is cut lengthwise in the middle in a vertical plane, then it is divided into two equal mirror halves i.e. opposite right and left halves. This symmetry may not be internal symmetry but definitely from outside. Examples of bilateral symmetry are frog, man, earthworms, insects etc. (most of the animals.)
(c) Radial symmetry : In this symmetry when an animal is cut through its longitudinal axis through any diameter, then body will have two equal halves, e.g. hydra, star fish etc.
3. Body cavity or Coelom : Animals which have tube within a tube body plan have body cavity or coelom. Their cavity is filled with the fluid. This is known as body coelom.
Body flexibility is given by coelom. All the internal organs are suspended in the coelom and acts as body absorb.
Except in roundworms, the coelom develops from embryonic mesoderm in all animals. Porifers. coelenterates and platyhelminthes do not have coelom, hence also known as acoelomates.
4. Body segmentation : In some animals the body has several segments. Body segments are found in annelids, arthopods and chordates.
5. Body support and protection : Formenifera (protozoans), Coelenterates, arthopods and most of the molluscans are soft bodied organisms. They are provided with exoskeleton. The exoskeleton is formed by the deposition of hard substances or shell. The exoskeleton is also present in the vertebrates such as scales, feathers, hairs, nails etc.
Exoskelaton of the body especially of vertebrates is made of hard, bony and cartilaginous tissue. Notochord supports the body of primitive adult chordates whereas vertebral column is a supporting skeleton of vertebrates. Appendicular skeleton provides a means of locomotion and brain case (cranium) and vertebral column protects the central nervous system in vertebrates. The height or length of the animals is given by the axial skeleton.
Classification of animal Kingdom
Invertebrate phyla : Invertebrates are those animals which are devoid of notochord or vertebral column. Evolutionary studies of animals of same phylum have directly or indirectly originated from a single common ancestor.
Lower and higher invertebrates : The lower invertebrates have very simple body organisation and are generally small in body size. In this category come porifera, coelenterata, platyhelminthes and nematoda.
The higher invertebrates are mostly larger bodied animals and their body organisation is also complex. In this category come annelida, arthropoda, mollusca and echinodermata.
Classification of Animal Kingdom
Non-Chordates Phyum Chordata
or Invertebrates
Phylums Classes
Porifera Agnatha
(Sponges) (Jawless fish)
Cnidaria Chondrichthyes
(Coelenterates) (Cartilage fish)
Platyhelminthes Osteichthyes
(Flatworms) (Bony fish)
Nemathe- Amphibia
lminthes (Amphibians)
(Roundworms)
Annelida Reptilia (Reptiles)
(Segmented)
worms
Mollusca Aves (Birds)
(Mollusks)
Arthrophoda Mammalia
(Arthropods) (Mammals)
Echinodermata
(Echinoderms)
Phylum-Porifera
General characters
1. Habit and habitat : Aquatic animals, sedentary, mostly marine but some are found in fresh water also.
2. Body : Diploblastic and non-cellular mesenchyma layer between two layers is present. Cells are loosely arranged with tissue grade system.
3. Shape : Variable plant like.
4. Symmetry : Asymmetrical or Radial (mostly).
5. Minute pores are present on the surface in large numbers. These are openings of canal system. One large opening osculum forming the blind sac body plan.
6. Cellular organisation : Choanocytes form the interior living.
7. Canal system : Canal system maintains the water current in the body.
8. Mouth : Absent.
9. Digestion : Intracellular. These are biofilters.
10. Skeleton : Internal skeleton which is made of spicules and spongin fibres. These spicules are made up of silicon, calcium and spongin fibres and are proteinaceous in nature.
11. Sensation : Localised.
12. Locomotion : Absent.
13. Greatest power of regeneration.
14. Sex : Hermaphrodite or unisexual.
15. Reproduction : Asexual by buds and sexual by gametes.
16. Fertilization : Internal cleavage holoblastic.
17. Development : Indirect with ciliated larva. Two types—amphiblastula larva and parenchymula larva.
Classification
Class 1—Calcarea or Calcispongiae e.g. Leucosolenia, Grantia, Scypha, Sycon etc.
Class 2—Hexactinellida or Hyalospongiae e.g. Euplectella, Hyalonema.
Class 3—Demospongiae e.g. Cliona, Spongilla etc.
Phylum-Coelenterata
General characters
1. Tissue : It is low grade.
2. Habit and habitat : Exclusively marine and a few are fresh water. Solidary or colonial and sedentary or free living.
3. Symmetry : Symmetry is radial.
4. Tentacles : Encircle the mouth.
5. Body wall : Diploblastic and non-cellular intermediate supporting layer known as mesoglea.
6. Characteristic interstitial cells and nematocyst : Nematocyst serves for stinging, adhesive, offence and defence and food capture.
7. Gastro-vascular cavity : Lined with endoderm called coelenteron.
8. Digestion : Extracellular.
9. Skeleton : External or internal lining or in the form of sclerites or as continuous mass.
10. Locomotion : Locomotion is due due to smooth musle fibrils in the epithelial cells.
11. Nervous system : Primitive made up of diffused network of nerve cells and neurites in the body wall.
12. Body structure : Two types-polyp and medusa. Many species are provided with the phenomenon of alternation of generation.
13. Reproduction : Asexual reproduction by budding and sexual by ova and sperms.
14. Development : Indirect with stereogastrula known as planula.
Classification : It has more than 10,000 known species. It is mainly classified into three classes :
Class 1 : Hydrozoa e.g. Hydra, Obelia, Physalia.
Class 2 : Scyphozoa e.g. Aurelia, Cassiopeia.
Class 3 : Anthozoa e.g. Pennetula, Alcyonium, Metridium.
Phylum-Platyhelminthes
General characters
1. Symmetry : Bilateral with dorsoventrally flattened body with head present anteriorly.
2. Shape : Mostly worm-like but may be ribbon or broad leaf-like.
3. Size : The size is moderate but a few are of 10-15 meters.
4. Adhesive organs : Secretion or/and suckers; hooks etc.
5. Body covering : A syncytial, cellular and partly ciliated epidermis with cuticle only.
6. Skeleton : Absent but contains organs which are cuticularised with scleroproteins only. These hard organs are provided with hooks, spines, thorns, spicules etc. which are of cuticle.
7. Digestive system : Absent in acoela and flatworms but rest of these animals are provided with digestive system.
8. Excretory system : By protonephridia which have special type of cells called the flame cells.
9. Nervous system : Primitive type. Mainly consists of cerebral gangila or brain.
10. Sex : Hermaphrodite (mostly).
11. Reproductive system : Asexual reproduction in planaria is by fission and sexual reproduction by generalised formation of ova and sperm fusion.
12. Development : With a few larval stages.
Classification
Class 1 : Turbellaria e.g. Convoluta, Segmentata etc.
Class 2 : Trematoda e.g. Polystoma, Schistosoma, Fasciola etc.
Class 3 : Cestoda e.g. Phyllobothrium, Taenia, Protocephalus etc.
Phylum Nemathelminthes-The Roundworms
General Characters
1. Unsegmented Round body, tube-like or worm-like.
2. Triploblastic This class has three germ layers.
3. Body cavity is a pseudocoel.
4. Bilaterally symmetrical, elongated worms with pointed ends and have bilateral symmetry.
5. Alimentary canal is complete (tube within tube organisation) with mouth and anus.
6. Head : Well formed head.
7. Body wall is covered by a tough cuticle.
8. Well developed excretory system consists of protonephridia and canals to remove the wastes from the body.
9. Exhibit distinct sexual dimorphism. It means that sexes are separate.
10. Some are free living, others are important plant and animal parasites.
e.g., Ascaris, Wucheria, Enterobius are parasites and Rhabditis is free living in soil.
Phylum-Annelida
General characters
1. This phylum has worm’s body which is externally as well internally divided by a number of rings or anulii.
2. Body organisation is organ system grade in which organs form the system.
3. Symmetry : Triploblastic, bilaterally symmetrical, coelomate.
4. Locomotion : By chitinous setae or muscular parapodia.
5. Digestive system : System is well developed and has extracellular digestion.
6. Blood circulatory system : Circulatory system is closed type. Respiratory pigment dissolved in plasma.
7. Respiration : By moist or humid skin or parapodia or cephalic gills.
8. Excretory system : Segmentally arranged nephridia.
9. Nervous system : One pair of cerebral ganglia (or brain) and a double nerve cord with a pair of gangila in each segment.
10. Sense organs : Have touch organs, taste buds, statocyst, photosensitive cells and eye with lens.
11. Sex : Hermaphrodite or unisexual.
12. Development : Spiral cleavage and determinate type. If development is indirect then the name of larva is trochophore.
13. Habit and habitat : Mostly sea living, marine and fresh water. Some are terrestrial burrowings animal, some are symbiont and other are parasite.
Classification
Class 1 : Polychaeta e.g. Aphrodite, Nereis, Chaetopterus, Arenicola, Sabella.
Class 2 : Oligochaeta e.g. Tubifex, Lumbricus, Pheretima, Megascolex.
Class 3 : Hirudinea e.g. Glossiphonia, Hirudo, Hirudinaria.
Class 4 : Archiannelida e.g. Polygordius, Protodrillus.
Phylum-Arthropoda
General characters
1. Body organisation is organ grade system.
2. Symmetry : Bilateral symmetry, triploblastic, segmented body.
3. Locomotion : Movement is by segmented legs for walking. They have running and wings for flying.
4. Exoskeleton : Chitinous cutiularised which is periodically cast off.
5. Body is divided into head, thorax and abdomen. Fused head and thorax often and form cephalothorax.
6. Body : Haemocoel filled with haemolymph.
7. Digestion : Complete; mouth parts are adopted for differentially feeding mechanism.
8. Circulatory system : They have open system which contains a dorsal pericardial, a middle perivisceral and a ventral perineural sinus along with one heart, arteries and veins.
9. Respiration : Respiration from general body surface, gills, trachea and book lungs.
10. Excretory organs : Green glands and malpighian tubules.
11. Nervous system : One dorsal cerebral ganglia makes the brain ring and a double ventral nerve cord.
12. Sense organs : They have sense of touch and eyes are simple and compound.
13. Sex : Usually separated.
14. Reproduction : Paired gonads with ducts.
15. Fertilization : Fertilization is internal, oviparous and ovoviviparous.
16. Development : Direct or indirect with more than one larval forms. Some with parthenogenesis.
17. Habit and habitat : These are free living, aquatic and parasitic. The variety of habits and habitats are present in the animals of arthropods.
Classification
Class 1 : Mesostomata e.g. Limulus, Eurypterus, Pterygotus.
Class 2 : Arachnida e.g. Buthus, Palamnaeus (scorpion), Chelifer (pseudo scorpion), Lycosa (wolf spider), Achaearanea (House spider), Mites, ticks.
Class 3 : Crustacea e.g. Apus, Daphnia, Cypris cyclops, Argulus, Lepus, Balanus, Sacculina, Squilla, Myis, Oniscus, Caprella, Crab, Palaemon, Astacus (ray fish), Hippa, Cancer (crab), Euparagus or Hermit crab.
Class 4 : Diplopoda e.g. Millipede, Julus, Spirobolus.
Class 5 : Chilopoda e.g. Centipede, Scolopendra, Lithobius.
Class 6 : Insecta e.g. Silver fish, Lepisma, Periplaneta, Grylus, Cricket, Mantis, Phyllium (leaf insect), Termites, Dragon fly, Pediculus (sucking lice), Cimex, Bedbug, Aphids, Beetles, Moths, Butterflies, Musca (house fly), Apis (honey bee), Wasps etc.
Phylum-Mollusca
General characters
1. Body : Organ system grade.
2. Triploblastic : Coelomate, unsegmented except monoplacophora.
3. Symmetry : They have bilateral symmetry.
4. Shell : Monovalvular or bivalvular or absent or internal.
5. Body coelom : Restricted mainly to the pericardial, gonadal and renal sinuses.
6. Digestive system : Complete, glands, liver and hepatopancreas.
7. Circulatory system : Mainly closed type, but in some cases it is open type opens into some sinuses, heart with auricle and ventricle, haemocyanin is the respiratory pigment.
8. Respiratory system : Respiration by gills or lungs or both.
9. Excretion : It is by nephridia or kidney.
10. Nervous system : It contains paired ganglia, connectives and nerves.
11. Sense organs : Eyes, statocyst, sense or touch, smell and gustatory.
12. Reproductive system : Dioecious or monoecious, gonads with one or two ducts.
13. Fertilizatin : It may be External or internal.
14. Development : Direct development or with free swimming larval forms.
15. Habit and habitat : Terrestrial, aquatic, marine or fresh water.
Classification
Class 1 : Monoplacophora e.g. Neopilina.
Class 2 : Amphineura e.g. Chiton.
Class 3 : Scaphopoda e.g. Dentalium.
Class 4 : Gastropoda e.g. Patella, Pila, Cypraea (caurie), Aplysia, Doris, Limex slug, Helix and land snail.
Class 5 : Pelecypoda or Bivalvia or Lamellibranchia e.g. Ostrea, Mytillus, Pecten, Teredo (ship worm), Unio, Anodonta.
Class 6 : Cephalopoda or Siphonopoda e.g. Nautilus, Loligo, Sepia (cuttle fish), Octopus.
Phylum-Echinodermata
General characters
1. Body : Organ system grade.
2. Triploblastic : Coelomate.
3. Symmetry : Radial symmetry.
4. Body : Body is unsegmented, globular, star shaped, oval, disc shaped and extended lengthwise.
5. Pentamerous body surface radiated into ambulacral and interambulacral region alternately present.
6. Skeleton : Dermal spines or dermal calcarious stipules form the interskeleton.
7. Locomotion : For locomotion they have water vascular system with podia and tube-feet madreporite.
8. Body coelom : Enterocoelic type includes perivisceral coelom and water vascular cavities.
9. Alimentary canal : Alimentary canal is straight or coiled.
10. Circulatory system : Perihaemel blood vascular system.
11. Respiratory system : Includes branchial, tubefeet, respiratory tubes and burr sac.
12. Nervous system : Circum oral ring and radial nerves present and brain absent.
13. Sense organs : Organ of touch, chemoreceptors, internal tentacles, photoreceptors, statocyst very less developed.
14. Excretory system : Absent.
15. Sex : Mostly unisexual.
16. Reproductive organs : Large gonads and numerous gonoducts.
17. Fertilization External.
18. Development : Indirect with free swimming larval forms.
19. Regeneration power present.
20. Habit : All are marine.
Classification
Class 1 : Asteroidea e.g. Asterias, Solaster.
Class 2 : Ohiuroidea e.g. Ophiura, Ophiothrix, Ophioderms.
Class 3 : Echinoida e.g. Echius, Clypeaster.
Class 4 : Holothuroidea e.g. Cucumaria, Holothuria, Synepta.
Class 5 : Crinoidea e.g. Antedon, Neometra.
Phylum-Chordata
General characters
1. Fundamental chordate characters.
2. Common characters of chordates and non-chordates.
3. Advance chordate characters.
Fundamental chordate characters : These characters are present in any stage of life history. There are three morphological characters :
(i) Notochord or chorda dorsalis.
(ii) Dorsal tubular nerve cord.
(iii) Pharyngeal gill slits.
Common Characters of Chordates and Non-Chordates
(i) Axiation.
(ii) Bilateral symmetry.
(iii) Triploblastic condtion.
(iv) Coelom.
(v) Metamerism.
Advance chordate characters
(i) Living endoskeleton.
(ii) Efficient respiration.
(iii) Ventral heart.
(iv) Hepatic portal system.
(v) RBC or Erythrocytes.
(vi) Post anal tail.
(vii) Nervous sytem centralized.
Super class—Pisces
General characters
1. Habit and habitat : Aquatic, fresh water or marine. Fish are cold blooded vertebrates.
2. Skin : Covered with scales, bony plates or dermal denticles.
3. Body : They have streamlined body but some are elongated, a few are dorsoventrally compressed and others are snake-like.
4. Fins : Paired or unpaired fins with soft or spiny rays.
5. Endoskeleton : Bony and cartilaginous.
6. Respiratory organs : Gills, but accessory respiratory organs are also present. The gill slits open outside. These are covered in bony fishes. These gill slits are never more than seven.
7. Lateral line system : Line system is well developed.
8. Heart : Venous heart i.e., only deoxygenated blood is transported through the heart. Heart has two chambers viz. one auricle and one ventricle.
9. Excretory system : Two mesonephric type kidneys.
10. Cranial nerves : Ten pairs.
11. Ear : Internal ears.
12. Sex : Unisexual.
13. Development : Indirect.
14. Reproductive organs : One pair of gonads with gonoducts.
Classification
Class 1 : Elasmobranchii e.g. Scoliodon, Zygaena, Trygon, Pristis, Torpedo.
Class 2 : Holocephalii e.g. Chimaera.
Class 3 : Dipnoi e.g. Protopterus, Lepidosiren.
Class 4 : Teleostomi e.g. Latimeria, Polypterus, Amia (bow fish), Notopterus (knife fish), Labeo, Catla, Cyprinus, Heteropneustes, Clarias, Wallago, Mystus, Auguilla (Eel), Exocoetus (Flying fish), hippocampus (sea horse), Syngnathus (Pipe fish), Ophiocephalus, Anabas (climbing fish), Synaptura (flat fish, Echineis (remora), tetradon (Globe fish), Diodon (porcupine fish).
Class-Amphibia
General characters
1. Amphibians are cold blooded animals.
2. Skin : Smooth or rough glandular. Skin is kept moist by the glandular secretion.
3. Scales are hidden in the skin if present.
4. Skull : Two occipital condyles.
5. Vertebrae : Acentrous, notocentrous and pseudocentrous.
6. Limbs Tetrapodus and pentadactylus.
7. RBC : Biconvex, oval and nucleated.
8. Heart : Three chambered heart—one ventricle and two auricles with sinus venosus symmetrical aortic arches.
9. Gills : During early stages of development it is present.
10. Excretory organs : Mesonephric kidneys.
11. Lateral line system : It is present during some stages of development.
12. Cranial nerves : 10 pairs.
13. Development : Generally with aquatic larval forms.
The amphibians are primarily aquatic because they lay eggs in water and early development of life takes place in aquatic medium and secondarily they are land living. Amphibians are both water and land living.
Classification
Order 1 : Labyrinthodontia (extinct) e.g. Eryops.
Order 2 : Phyllospondyli (extinct).
Order 3 : Lepospondyli (extinct).
Order 4 : Gymnophiona or Apoda or Caecilia (living e.g. Ichthyophis (caecilian), Uraeothyphlus.
Order 5 : Condata or Urodela (living) e.g. Amblystoma, Salamandra (salamander), Triton, Proteus (blind salamander), Necturus (mud puppy), Siren (mud eel)
Order 6 : Anura or Salientia (living) e.g. Alytes (midwife toad), Pipa (Surinam toad), Bufo (Toad), Hyla (Tree frog), Rana tigrina (common frog), Rhacophorus (flying frog).
Class-Reptilia (Reptiles)
General characters
1. Reptiles are cold blooded, terrestrial and aquatic.
2. Body covering : With horny scales or scutes.
3. Skin : Skin is dry; do not have glands.
4. Limbs : Tetrapodus and pentadactylus.
5. Skull : Single occipital condyle.
6. Vertebrae : Gastrocentrous type ribs form a true sternum.
7. Respiration : Lungs are responsible for respiration.
8. Heart : Two auricles and incomplete divided ventricle.
9. Right and left aortic arches are complete.
10. RBC : Nucleated.
11. Excretory organs : Each metanephric kidney is provided with a separate ureter.
12. Cranial nerves : 12 pairs.
13. Fertilization : Internal fertilization and development on land.
14. Cloaca : Typical.
Classification
Sub-class 1-Anapsida e.g. Seymouria, Chelone (marine turtle or green turtle), Trionyx (soft shelled fresh water terrapin), Testudo (land tortoise).
Sub-class 2-Parapsida e.g. Ichthyosaurus.
Sub-class 3-Diapsida e.g. Sphenodon (Tuatara), Hemidactylus (common wall lizard or Gecko), Calotes (blood sucker or garden lizard), Chameleon (garden coloured lizard), Draco (flying lizard or dragon), Phrynosoma (horned lizard or horned toad), Varanus (monitor lizard), Heloderma (poisonous lizard or Gila monster), Typhlops (blind snakes), Python, Eryx johni (sand boa), Ptyas (rat snake), Tropidonotus (grass snake), Bungarus (krait), Naja naja (cobra), Naja hannah (king cobra), Hydrophis (sea snake), Viper, Natrix, Crocodylus palustris (muggar), Alligator, Gavialis gangeticus (gharial).
Sub-class 4-Synapsida e.g. Cynognathus.
Class-Aves
General characters
1. These are warm blooded animals.
2. Exoskeleton of feather.
3. Limbs : They have forelimbs modified into wings provided with feathers for flight. Hindlimbs adopted for walking or swimming and perching.
4. Skin : Tail has oil glands.
5. Skeleton : Spongy and light weight.
6. Skull : Monocondylic.
7. Break : Horny without teeth in living birds.
8. Vertebrae : Heterocoelus but may be amphicoelus or procoelus. Cervical and thoracic (some) free, posterior thoracic lumbar and saccral fused certain fused caudals form the pygostyle.
9. Ribs : Double headed with uncinate process.
10. Sternum : Usually with keel for the attachment of flight muscles.
11. Carpo-meta carpus : Distal carpals and metacarpals.
12. Tibiotarsus : Fusion of proximal tarsal and tibia tarsometatarsus—fusion of metatarsals with distal tarsals.
13. Digestive system : Crop (a storage organ) is formed by the gullet. Stomach divided into glandular system and muscular system. Cloaca true with three chambers.
14. Respiratory organs : Spongy and non-distensible lungs. air sacs present and communicate with the air cavities in the bones.
15. Sound production : By a swollen part syrinx.
16. Heart : Contain four chambered heart, double circulatory. Only right aortic arches are present.
17. RBC : Oval and nucleated.
18. Excretory organs : Metanephric; three lobed excretory duct, the ureters open directly into cloaca.
19. Brain : Most developed Cerebellum.
20. Sex : Separate.
21. Reproductive organs : Only left ovary is present.
22. Fertilization : Internal.
23. Eggs : Large with yolk (megalecithal).
Classification
Sub-class 1-Archaeornithes or Palaeornithes (extinct) e.g. Archaeopteryx and Archaeornis.
Sub-class 2-Neornithes (living and extinct birds) e.g. Hesperornis (extinct), Struthio camelus (ostrich), Apteryx (kiwi), Tadorna tadorna (common shell duck), Cygnus olor (mute swan), Gyps fulvus (Griffon vulture), Haliastur indus (brahminy kite), Aquila chrysaetos (golden eagle), Accipiter nisus (Eurasian sparrow hawk), Falco peregrinus (peregrine falcon), Pavo cristatus (peacock), Columba livia (common pigeon), Psittacula krameri (green parrot), Bubo bubo (herred owl), Calypte and (humming bird-smallest bird), Apus melba (alpine swift), Passer domesticus (common house sparrow), Eudynamis scolopaceous (koel), Alcido atthis (kingfisher), Corvus splendens (common house crow), Orthotomus sutorius (tailor bird), Ploceus philippinus (weaver bird or baya).
Class-Mammalia
General characters
1. These are warm blooded.
2. Skin : Covered with hairs with sweat glands and sebaceous (oil) glands.
3. Mammary glands : Present. Females feed young ones.
4. Teeth : Heterodont, thecodont, diphydont.
5. Skull : Dicondylic.
6. Lower jaw : Of dentary.
7. Vertebrae : Amphiplatyan, seven cervical vertebrae.
8. Ribs : Double headed.
9. Limbs : Either plantigrade or digitigrade or unguligrade.
10. Muscular diaphragm : Separates the thoracic cavity with abdominal cavity.
11. Heart : Four chambered, double circulatory. Only left aortic arch is present.
12. RBC : Biconcave, non-nucleated.
13. Ear : External (pinna), middle and internal ear.
14. Brain : Four optic lobes (corpora guadrigemina).
15. Excretory organs :Metanephric type.
16. Viviparous : Generally oviparous in monotremata.
Classification
Sub-class 1-Prototheria (primitive, egg laying mammals) e.g. Echidna (spiny ant-eater), Ornithorhynchus.
Sub-Class 2-Theria e.g. Macropus major (Australian kangaroo), Erinaceous (hedgehog), Talapa (mole), Pteropus (flying fox), Lemur, Loris, Ateles (spider monkey), Ape, Homo sapiens (man), Pan (chimpanzee), Oryctolagus cuniculus (rabbit), Lepus (hare), Manis crassinadata (Indian pangolin), Funambulus (squirrel), Rattus rattus (house rat), Balaenoptera musculus (Blue whale), Delphinus delphis (common dolphins), Panthera leo persica (asiatic lion), Panthera tigris (tiger), Canis familiaris (dog), Canis lupas (wolf), Canis aureus (jackal), Vulpes benghalensis (Indian fox), Acinonyx jubetus (cheetah), Felis domesticus (domestic cat), Herpestes (mongoose), Phoca (seal), Panthera pandus (leopard), Elephas maximus (asiatic elephant), Equus cabalus (horse), Equus zebra (zebra), Hippopotamus (horse of silver), Sus (pig), Camelus (camel), Bos indicus (cow), Bubalus bubalis buffalo), Capra (goat), Ovis (sheep), Giraffe, Cervus (deer), Antelope etc.
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