Kingdom Animalia

4.1 Criteria Used for Animal Classification

Animals are classified based on the following criteria:

4.2 Animal Body Plan

A. Cell Aggregate Plan

Cells do not form true tissues or organs.

Cells show minimal differentiation and division of labour.

Found in Phylum Porifera (sponges).

Cells are loosely organised and perform different functions without forming true tissues.

B. Blind Sac Body Plan

Body is sac-like with a single opening.

Digestion occurs inside the sac-like cavity.

Ingestion and egestion occur through the same opening.

Example: Phylum Cnidaria.

C. Tube-within-Tube Body Plan

The digestive system forms a tube within the body.

Mouth and anus are separate openings at opposite ends of the digestive tract.

Food enters through the mouth and undigested waste exits through the anus.

Found in Phylum Annelida onwards.

4.3 Animal Classification

1. Phylum Porifera

Meaning: Pori = pores; feron = bearing

Examples: Scypha, Euspongia (bath sponge), Euplectella (Venus' flower basket)

General Characteristics

Habitat: Aquatic; mostly marine, few freshwater.

Commonly called sponges.

Symmetry: Mostly asymmetrical.

Organisation: Cellular level; cells show little division of labour. Body resembles a colony of different types of cells.

Nature: Sedentary (remain attached to a surface).

Canal System (Water Flow)

Body has numerous minute pores called ostia → water enters.

Water enters the body cavity called spongocoel.

Water exits through a single large opening called osculum.

Water circulates through the canal system.

Functions of Water Circulation

Food absorption

Exchange of respiratory gases

Removal of excretory products

— Additional Characteristics

1. Choanocytes (Collar Cells)

Spongocoel is lined by special flagellated cells called choanocytes or collar cells.Beating of flagella creates a water current.

2. Body Support The body is supported by:

Spicules: Made of calcium carbonate (calcareous) or silica (siliceous). Spongin fibres: Made of protein.

3. Reproduction

Asexual - Fragmentation and gemmule formation

Sexual - Formation of gametes

Regeneration: Ability to regrow lost or damaged body parts.

Fertilization: Internal.

Development: Indirect, involving a larval stage

2. Phylum Cnidaria

Examples: Hydra

Aurelia — Jellyfish

Physalia — Portuguese man-of-war

Adamsia — Sea anemone

Diploria — Brain coral

Gorgonia — Sea fan

General Characteristics

Habitat: Aquatic; mostly marine, with a few freshwater forms.

Nature: Sessile (attached) or free-swimming.

Symmetry: Radial symmetry.

Germ layers: Diploblastic.

Body plan: Blind-sac body plan; one opening for ingestion and egestion.

Body Forms

Polyp - Cylindrical body; usually sessile - Hydra

Medusa - Umbrella-shaped body; usually free-swimming - Aurelia

Gastrovascular Cavity

The body cavity is called the gastrovascular cavity or coelenteron.

Functions in digestion and circulation.

Cnidoblasts (Stinging Cells)

Present on tentacles.

Functions: Anchorage, offence and defence.

Reproduction

Asexual reproduction: Budding and regeneration.

Sexual reproduction: Formation of gametes.

Metagenesis

Definition: Alternation between polypoid and medusoid generations.

Polyp → Medusa: Asexual reproduction.

Medusa → Polyp: Sexual reproduction.

Example: Obelia.

3. Phylum: Ctenophora

Examples: Pleurobrachia, Ctenoplana

General Characteristics

Common name: Comb jellies / Sea walnuts.

Habitat: Exclusively marine (only found in the sea).

Nature: Free-swimming.

Body: Diploblastic (two germ layers), radially symmetrical (body parts arranged around a central axis).

Body plan: Blind-sac (one opening for ingestion and egestion).

Organisation: Tissue level (cells form tissues).

Locomotion

Eight rows of ciliated comb plates (rows of tiny hair-like structures that help in movement).

Special Features

Bioluminescence (production of light by a living organism).

Digestion: Extracellular (outside cells) and intracellular (inside cells).

Colloblasts (sticky cells that capture prey) are present.

Cnidoblasts (stinging cells) are absent; hence, called Acnidarians (without cnidoblasts).

Considered a minor phylum (contains very few members).

Reproduction

Sexual reproduction.

Indirect development (development through a larval stage).

4. Phylum: Platyhelminthes

Meaning: Platy = flat; helminth = worms

Examples: Planaria, Taenia (tapeworm), Fasciola (liver fluke)

General Characteristics

Body: Dorsoventrally flattened (flattened from top to bottom); hence, called flatworms.

Body cavity: Acoelomate (no body cavity).

Germ layers: Triploblastic (three germ layers).

Organisation: Organ-system level (organs work together in systems).

Habitat: Mostly endoparasitic (live inside a host); some are free-living.

Adaptations in Parasitic Forms

Hooks and suckers: Help attach to the host's body.

Body covering: Cuticle (protective outer covering) in parasites; cilia (tiny hair-like structures) in free-living forms.

Digestive system: Generally absent in parasites; incomplete (one opening) in free-living forms.

Excretion and Osmoregulation

Flame cells / Protonephridia: Help in excretion (removal of wastes) and osmoregulation (maintenance of water and salt balance).

Reproduction

Hermaphrodite (bisexual): Both male and female reproductive organs occur in the same individual.

Self-fertilisation: Fusion of gametes from the same individual.

Regeneration: Ability to regrow lost body parts; highly developed in some forms.

Polyembryony: Formation of more than one embryo.

5. Phylum: Aschelminthes / Nemathelminthes

Meaning: Aschelminthes: Ascus = sac; helminth = worm.

Nemathelminthes: Nema = thread.

Examples: Ascaris (roundworm), Wuchereria (filarial worm), Ancylostoma (hookworm).

General Characteristics

Habitat: Mostly parasitic (live in a host); some free-living.

Body: Long, cylindrical, thread-like and circular in cross-section; hence, called roundworms.

Symmetry: Bilateral symmetry (one plane divides body into equal halves).

Germ layers: Triploblastic (three germ layers).

Body cavity: Pseudocoelomate (body cavity not completely lined by mesoderm).

Body plan: Tube-within-tube (separate mouth and anus).

Body covering: Tough, resistant cuticle (protective outer layer).

Muscles: Longitudinal muscles present; circular muscles absent.

Digestive System 

Complete alimentary canal: Mouth and anus at opposite ends.

Pharynx: Well-developed and muscular (helps move food).

Excretion and Nervous System

Excretion: Through canals or gland cells; waste leaves via the excretory pore.

Nervous system: Nerve ring and nerves.

Reproduction

Unisexual: Male and female sexes are separate.

Sexual dimorphism: Males and females differ in appearance.

Example: Ascaris

Female: Longer and broader, with a straight posterior end.

Male: Shorter and narrower, with a curved posterior end and a pair of penial setae (copulatory structures used during mating).

Fertilization: Internal.

Development: May or may not include a larval stage.

6. Phylum: Annelida

Meaning: Annulus = ring

Examples: Nereis, Pheretima (earthworm), Hirudinaria (leech)

General Characteristics

Common name: Ringworms / Segmented worms.

Habitat: Aquatic, free-living, ectoparasitic (live on the host's outer surface) or burrowing in moist soil.

Symmetry: Bilateral symmetry (one plane divides the body into equal halves).

Segmentation: Metameric segmentation (body divided into repeated segments).

Clitellum: Special body region involved in reproduction, especially cocoon formation.

Locomotion

Movement occurs with the help of longitudinal and circular muscles.

Examples : Setae (bristle-like structures) in Earthworm

Parapodia (paired lateral appendages) in Nereis

Suckers (structures for attachment) in Leech

Body Systems

Digestive system: Complete alimentary canal (separate mouth and anus).

Respiration: Gas exchange through the body wall.

Circulation: Closed circulatory system (blood remains within vessels).

Excretion and osmoregulation: Nephridia (excretory organs that remove waste and regulate water balance).

Nervous system: Nerve ring and ventral nerve cord.

Ventral: Located on the underside.

Solid and ganglionated: Solid cord containing groups of nerve cells called ganglia.

Reproduction

Mostly hermaphrodites (one individual has male and female reproductive organs).

Some are dioecious (sexes are separate).

Example: Nereis is dioecious.

7. Phylum: Arthropoda 

General Characteristics

Largest phylum of Kingdom Animalia.

Meaning: Arthro = joint; poda = appendages (jointed limbs).

Habitat: Omnipresent (found almost everywhere).

Nature: Solitary (live alone) or colonial (live in groups); mostly free-living.

Barnacles: Sessile (remain attached to a surface).

Some are parasitic; some are sanguivorous (feed on blood), e.g. female mosquito and bedbug.

Symmetry: Bilateral symmetry (one plane divides the body into equal halves).

Germ layers: Triploblastic (three germ layers).

Body cavity: Eucoelomate (true body cavity lined by mesoderm).

Segmentation: Metamerically segmented (body divided into repeated segments).

Body plan: Tube-within-tube.

Organisation: Organ-system level.

Body Covering

Covered by a tough, non-living chitinous exoskeleton (hard outer covering made of chitin).

Moulting / Ecdysis: Periodic shedding of the old exoskeleton to allow growth.

Body Division: Body is generally divided into:

Head

Thorax

Abdomen

Body Systems

Digestive system: Complete (separate mouth and anus).

Circulatory system: Open type (blood flows through the body cavity called haemocoel).

Respiration: Through gills, trachea, book lungs or book gills.

Excretion: Through green glands, Malpighian tubules or coxal glands.

Nervous system: Nerve ring + double, ventral, ganglionated nerve cord (nerve cord containing groups of nerve cells called ganglia).

Sense organs: Well-developed; include antennae, simple or compound eyes and various receptors.

Reproduction

Sexes: Separate; show sexual dimorphism (males and females differ in appearance).

Fertilization: Generally internal.

Development: Direct or indirect through metamorphosis (change in body form during development).

Parthenogenesis: Offspring develop without fertilization; occurs in some arthropods, e.g. honey bees and bugs.

Polymorphism: Different forms within the same species, e.g. honey bees, ants and termites.

Economic Importance

Lac insect (Laccifer lacca): Produces lac.

Lobsters, prawns and crabs: Used as food.

Silkworm: Produces silk.

Honey bee (Apis): Produces honey and wax.

Harmful Arthropods

Mosquito: Acts as a vector (organism that transmits disease-causing pathogens).

Locust (Locusta): Gregarious pest (forms groups and damages crops).

Special Fact

King crab (Limulus): Known as a living fossil (organism that has retained many ancient characteristics over a long period).

8. Phylum: Mollusca

Meaning: Mollis = soft

Examples: Pila (apple snail), Bivalve, Octopus (devil fish) , Sepia (cuttlefish), Chaetopleura (chiton) , Pinctada (pearl oyster), Loligo (squid), Aplysia (sea hare), Dentalium (tusk shell)

General Characteristics

Second-largest phylum of Kingdom Animalia.

Habitat: Mostly aquatic or found in marshy places; a few are terrestrial.

Nature: Free-living or sedentary (remain attached or in one place).

Body plan: Tube-within-tube.

Symmetry: Mostly bilateral; some are asymmetrical due to torsion (twisting of the body during development).

Body: Soft-bodied.

Body Structure

The body is divided into three parts:

Head: Contains sensory organs and, in many species, the mouth.

Foot: Muscular structure on the ventral side (underside); helps in movement.

Visceral mass: Contains internal organs.

Mantle and Shell

Mantle: Thick, muscular fold of the body wall that encloses the visceral mass.

The mantle secretes a hard calcareous shell (calcium carbonate shell).

Shell may be:

External — outside the body.

Internal — inside the body.

Absent — in some molluscs.

1. Digestive System

Complete digestive tract: Anterior mouth and posterior anus.

Radula: Rasping organ (scrapes food) in the buccal cavity, with transverse rows of teeth.

2. Respiration

Aquatic forms: Feather-like gills called ctenidia, present in the mantle cavity.

Mantle cavity: Space between the mantle and visceral mass.

Terrestrial forms: May possess lungs.

3. Circulatory System

Generally open type (blood flows through body spaces).

Exception: Sepia has a closed circulatory system.

Haemocyanin: Copper-containing blue respiratory pigment that transports oxygen.

4. Excretion

Through kidneys, also called organs of Bojanus.

5. Nervous System

Consists of three pairs of ganglia (groups of nerve cells).

Ganglia are interconnected by:

Commissures: Connections between ganglia on the same side or corresponding regions.

Connectives: Connections between different ganglia.

6. Sense Organs

Eyes - Vision

Tentacles - Tactile sensation (sense of touch)

Osphradia - Test water quality/purity

7. Reproduction

Sexes: Separate.

Mostly oviparous: Lay eggs.

Development: Direct or indirect (may involve a larval stage).

8. Economic Importance

Pearl oyster: Produces precious pearls.

Many molluscs are edible.

Mollusc shells are a rich source of calcium.

9. Phylum: Echinodermata

Meaning: Echinus = spines; Derma = skin.

Examples: Asterias (sea star), Cucumaria (sea cucumber), Echinus (sea urchin), Antedon (sea lily), Ophiothrix (brittle star).

Habitat: Exclusively marine; solitary or gregarious (living in groups); sedentary or free-living; mostly benthic (living at the bottom of the sea).

Symmetry: Radial symmetry with pentamerous symmetry (body parts arranged in multiples of five).

Body shape: Spherical, elongated or star-shaped; no distinct body divisions.

Body surfaces: Oral surface (side with mouth) and aboral surface (side opposite the mouth).

Endoskeleton: Made of calcareous ossicles (small calcium-containing skeletal plates); spines are present on the body.

Water vascular system: A characteristic feature; water enters through the madreporite (sieve-like plate). It helps in locomotion, food capture and respiration.

Digestive system: Complete; mouth is on the oral surface, while the anus is generally on the aboral surface.

Respiration: Through peristomial gills (around the mouth), papillae (thin body projections) and respiratory trees.

Circulatory system: Absent.

Excretory system: Absent.

Nervous system: Simple; consists of a nerve ring around the mouth and radial nerves in the arms.

Sexes: Usually separate; sometimes bisexual.

Fertilization: External.

Development: Indirect (larval stage present).

Regeneration: High power of regeneration (ability to regrow lost body parts).

10. Phylum: Hemichordata

Meaning: Hemi = half; Chordata = rod.

Examples: Balanoglossus, Saccoglossus.

General Characteristics

Classification: Earlier considered a subphylum of Chordata because the buccal diverticulum was mistaken for a notochord. Now classified as a separate phylum under Non-chordata.

Habitat: Exclusively marine; usually live in burrows at the sea bottom. Mostly free-living; Rhabdopleura is sedentary (remains attached).

Body: Soft, worm-like (vermiform), unsegmented and divided into three parts:

Proboscis – front part.

Collar – middle part.

Trunk – main body region.

Buccal diverticulum: A rod-like extension of the buccal cavity (mouth cavity); some scientists considered it a notochord.

Digestive system: Complete; alimentary canal is straight or U-shaped.

Respiration: Through numerous gills arranged in two longitudinal rows in the pharyngeal region. These open outside through gill slits.

Circulatory system: Simple and open type.

Excretion: Through the glomerulus (excretory structure).

Nervous system: Nervous tissue is embedded in the epidermis (outer body layer) on both dorsal and ventral sides.

Sexes: Usually separate; sometimes bisexual.

Fertilization: External.

Development: Indirect, through a free-swimming larva.

Significance: Considered a connecting link between non-chordates and chordates.

11. Phylum: Chordata

Characteristic Features

Chordates are identified by the presence of:

Notochord – at least during early embryonic life.

Pharyngeal gill slits – openings in the pharyngeal (throat) region.

Dorsal hollow nerve cord – a hollow nerve cord running along the dorsal side of the body.

Ventral heart – heart located on the ventral (underside) of the body.

Classification

Chordata is divided into three subphyla:

Urochordata

Cephalochordata

Vertebrata

Protochordates: Urochordata and Cephalochordata together are called protochordates.

A. Subphylum: Urochordata or Tunicata

Examples: Herdmania, Salpa, Doliolum.

Common names: Tunicates or ascidians.

Habitat: Exclusively marine.

Body covering: Soft body covered by a test or tunic (protective outer covering) made of tunicine.

Notochord: Present only in the larval tail; hence the name Urochordata. It disappears during metamorphosis (transformation from larva to adult).

Pharynx: Contains numerous gill slits.

Circulatory system: Closed type.

Development: Indirect (larval stage present).

B. Subphylum: Cephalochordata

Example: Branchiostoma (Amphioxus or Lancelet)

Habitat: Exclusively marine; partly buried in soft marine sediments.

Body: Small, fish-like animals, rarely exceeding 5 cm in length.

Notochord: Extends throughout the body and remains present throughout life.

Myotomes: Muscle blocks present along the body.

Post-anal tail: Present (tail extends beyond the anus).

Circulatory system: Closed type.

Blood: Lacks respiratory pigment.

C. Subphylum: Vertebrata

Notochord: Replaced by a cartilaginous or bony vertebral column (backbone).

Divisions:

1. Agnathostomata – jawless vertebrates.

2. Gnathostomata – vertebrates with jaws.

1. Division: Agnathostomata

Includes the most primitive living vertebrates, which lack jaws.

Includes one living class: Cyclostomata.

Class: Cyclostomata

Meaning: Cyclos = circular; stoma = mouth.

Examples: Petromyzon (lamprey), Myxine (hagfish).

Characteristics:

Body: Jawless and eel-like.

Skin: Soft and smooth, with unicellular mucus glands; scales are absent.

Fins: Median fins present; paired fins absent.

Mode of life: Ectoparasites (live on the outer body of a host).

Mouth: Circular, sucking mouth without jaws.

Skeleton: Cranium (skull) and vertebral column are made of cartilage.

2. Division: Gnathostomata

Meaning: Jawed vertebrates.

It is divided into two superclasses:

Pisces: Fishes (bear fins).

Tetrapoda: Animals that bear four limbs.

A. Superclass: Pisces

General Characteristics

Habitat: Aquatic.

Body temperature: Poikilothermic (body temperature changes with surrounding temperature).

Lateral line system: Contains rheoreceptors (sensory receptors that detect water currents).

Locomotion: By body muscles and fins; the caudal fin acts like a steering wheel.

Exoskeleton: Dermal scales (scales formed in the skin).

Endoskeleton: Bony or cartilaginous.

Body shape: Streamlined, boat-shaped body reduces water resistance during swimming.

Respiration: Through gills.

Heart: Two-chambered and ventrally located.

Circulation: Single and closed circulation. The heart contains only deoxygenated blood; hence, it is called a venous heart.

Brain: Well-developed, with large olfactory lobes (associated with smell).

Sexes: Separate.

Reproduction: Most are oviparous (lay eggs); some are viviparous (give birth to young ones).

Classification of Pisces

Superclass Pisces is divided into two classes.

1. Class: Chondrichthyes

Meaning: Chondron = cartilage; Ichthyes = fish.

Examples:Scoliodon – Dogfish, Pristis – Sawfish, Electric ray, Common skate, Hammerhead shark

2. Class: Osteichthyes (Bony Fishes)

Examples of Bony Fishes

Exocoetus (flying fish), Hippocampus (sea horse), Pomfret, Labeo rohita (Rohu), Catla (Katla), Clarias (Magur), Betta (fighting fish), Pterophyllum (angelfish) and aquarium fishes.

Meaning: Fishes with a bony endoskeleton.

Habitat: Aquatic; found in freshwater and marine water.

Endoskeleton: Bony.

Exoskeleton: Cycloid (smooth-edged) or ctenoid (comb-edged) scales.

Mouth: Mostly terminal (located at the front end).

Caudal fin: Homocercal (two externally equal lobes).

Gills: Four pairs of gill slits, covered by an operculum (bony gill cover).

Air bladder: Present; helps maintain buoyancy (ability to float at a particular depth).

Claspers: Absent (paired reproductive organs found in male cartilaginous fishes).

Fertilization: External.

Reproduction: Oviparous (egg-laying).

B. Superclass: Tetrapoda

Meaning: Animals that generally possess two pairs of limbs.

Some animals, such as snakes, are secondarily limbless (their ancestors had limbs, but these were lost during evolution).

Includes four classes: Amphibia, Reptilia, Aves and Mammalia.

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1. Class: Amphibia

Meaning: Amphi = both; bios = life.

Examples: Rana (frog), Bufo (toad), Salamandra (salamander), Ichthyophis (limbless amphibian), Hyla (tree frog).

General Characteristics

Habitat: Live on land and in freshwater.

Body temperature: Poikilothermic (changes with surrounding temperature).

Body divisions: Head and trunk; neck and tail are usually absent in adults, with a few exceptions.

Limbs: Two pairs arise from the pectoral and pelvic girdles and help in locomotion.

Skin: Moist and glandular, containing mucus glands.

Exoskeleton: Absent.

Eyes and ears: Eyelids present; tympanum (eardrum) represents the ear.

Cloaca: Common chamber through which digestive wastes, excretory products and gametes are released.

Circulatory system: Closed; heart is ventral and three-chambered (two auricles and one ventricle).

RBCs: Biconvex and nucleated.

Respiration: Through skin, lungs and buccopharynx (mouth–throat cavity).

Nervous system: Well-developed.

Sexes: Separate.

Reproduction: Oviparous (egg-laying); fertilization is external.

Development: Indirect, through an aquatic larval stage; metamorphosis occurs (larva changes into adult).

2. Class: Reptilia

Meaning: Repere = to creep or crawl.

Examples: Naja naja (cobra), Hemidactylus (wall lizard), Chelonia (turtle), Crocodilus (crocodile), Testudo (tortoise), chameleon (tree lizard), Bungarus (krait), Vipera (viper).

General Characteristics

Habitat: First true terrestrial vertebrates; some are aquatic or semi-aquatic and may live in marshy areas.

Locomotion: Usually by two pairs of limbs. Limbs are pentadactyl (having five digits), and digits bear claws. Snakes are limbless and crawl on their belly.

Body temperature: Poikilothermic.

Skin: Dry, non-glandular and covered with epidermal scales, scutes, shields or plates.

Shedding of skin: Lizards and snakes shed their skin periodically.

Ear: Tympanum present.

Heart: Two complete auricles, but ventricles are incompletely divided; therefore, the heart is not perfectly four-chambered. Exception: Crocodile has a four-chambered heart.

Brain: Well-developed; olfactory lobes and cerebellum are better developed than in amphibians.

Sexes: Separate, with prominent sexual dimorphism (visible differences between males and females).

Fertilization: Internal.

Reproduction: Mostly oviparous; viper is an exception in the textbook, listed as viviparous (giving birth to young ones).

Parental care: Present.

3. Class: Aves

Meaning: Avis = bird.

Examples: Columba (pigeon), Psittacula (parrot), Struthio (ostrich), kiwi, Aptenodytes (penguin), Corvus (crow), Neophron (vulture), Passer (sparrow).

General Characteristics

Limbs: Forelimbs are modified into wings for flying; some birds, such as ostriches, are flightless. Hind limbs help in walking, running and clasping tree branches.

Aquatic birds: Ducks have webs between their toes.

Body shape: Streamlined (boat-shaped) to reduce air resistance during flight.

Body temperature: Homeothermic (maintains a constant body temperature).

Exoskeleton: Feathers; scales are present on hind limbs.

Body divisions: Head, neck, trunk and tail.

Skin: Thin, dry and non-glandular, except for the uropygial gland (oil gland at the base of the tail).

Bones: Hollow, air-filled bones called pneumatic bones, which reduce body weight.

Jaws: Toothless and modified into a beak.

Digestive system: Crop (temporary food storage) and gizzard (grinds food) are present.

Blood: Red due to red blood cells; RBCs are biconvex and nucleated.

Heart: Perfectly four-chambered; double circulation occurs.

Respiration: Through lungs, with air sacs that aid efficient respiration and may also help reduce body density.

Brain: Enlarged, with a well-developed cerebellum for balance and coordination.

Sexes: Separate, with prominent sexual dimorphism (differences between males and females).

Reproduction: Oviparous (egg-laying); fertilization is internal.

Parental care: Highly developed.

Migration: Seasonal migration occurs in some birds.

Special Features

Urinary bladder: Absent, helping reduce body weight.

Female reproductive system: Usually only the left ovary and left oviduct are functional, reducing body weight.

4. Class: Mammalia

Meaning: Mammae = breasts or nipples.

Examples

Common mammals: Bat, Rattus (rat), Macaca (monkey), Camelus (camel), whale, human, Canis (dog), Felis (cat), Elephas (elephant), Equus (horse), Pteropus (flying fox).

Oviparous mammal: Ornithorhynchus (platypus).

Viviparous example: Macropus (kangaroo).

General Characteristics

Mammary glands: Milk-producing glands nourish the young; these are modified sweat glands.

Distribution: Omnipresent (found in a wide range of habitats).

Habitat: Mostly terrestrial; some aquatic, while others are aerial or arboreal (tree-dwelling).

Limbs: Used for walking, flying, climbing, burrowing and swimming.

Body divisions: Head, neck, trunk and tail.

Body temperature: Homeothermic (maintains a constant body temperature).

Exoskeleton: Includes hair, fur, nails, hooves and horns.

Skin: Glandular, with sweat glands and sebaceous glands (oil-producing glands).

External ear: Pinna (external ear flap) is present.

Dentition: Heterodont (different types of teeth, such as incisors, canines, premolars and molars).

RBCs: Biconcave (disc-shaped with a depression on both sides) and enucleated (without a nucleus).

Blood: Red in colour.

Heart: Ventral in position and four-chambered.

Respiration: Through lungs.

Brain: Highly developed; cerebrum has a transverse band called the corpus callosum (connects the two cerebral hemispheres).

Reproduction in Mammals

Oviparous: Lay eggs; e.g. duck-billed platypus (Ornithorhynchus).

Marsupials: Have a pouch in which immature young develop; e.g. kangaroo.

Placental mammals: The majority are placental and viviparous (give birth to young ones). The placenta helps exchange nutrients, oxygen and waste between mother and developing young.