Animal Kingdom NEET Notes

Animals are multicellular and heterotrophic. Animal kingdom is most diverse than the plant kingdom.

BASIS OF CLASSIFICATION

Levels of organization

3 levels (based on organization of cells):

• Cellular level of organization: Here the cells are arranged as loose cell aggregates. E.g. Poriferans.

• Tissue level of organization: Here the cells are arranged into tissues. E.g. Cnidarians and Ctenophores.

• level of organization: Here the tissues are arranged into organs and the organs are associated to form organ systems. Each system performs a specific physiological function. E.g. All higher animals (from Platyhelminthes to chordates). Organ systems of different animals show complexities. 

• Digestive system of cnidarians and Platyhelminthes is incomplete (i.e. it has only a single opening which serves as both mouth and anus). Complete digestive system has 2 openings (mouth & anus).

• Circulatory system is 2 types (open and closed).

Body symmetry

It is the arrangement of similar body parts on 2 sides of main axis of body. Based on symmetry animals are 2 types: Asymmetrical and Symmetrical.

• Asymmetrical: Here, body cannot be divided into 2 similar parts. E.g. Certain Poriferans, Snails etc.

• Symmetrical: Here, body can be divided into 2 similar parts. It is 2 types.

• Radial symmetry: Body can be divided into 2 similar parts by any plane along oral aboral axis of body. E.g. some Poriferans, Cnidarians, Ctenophores and Echinoderms.

• Bilateral symmetry: Body can be divided into 2 right and left halves by a section passing through the longitudinal axis. E.g. All vertebrates and many invertebrates. The body of bilaterally symmetrical animal has an upper or vertebral dorsal side, a lower ventral side, left and right lateral sides, anterior (cephalic) side and posterior (anal) side.

Germ layers

These are layers of gastrula from which all the body organs are formed. Based on the number of germ layers, animals are 2 types- Diploblastic and Triploblastic.

• Diploblastic animals: 2 germ layers- outer ectoderm and inner endoderm. E.g. Sponges and Coelenterates.

• Triploblastic animals: 3 germ layers- Outer ectoderm, middle mesoderm and inner endoderm. E.g. Flat worms to mammals.

Coelom (body cavity)

It is the space between body wall and gut wall. Coelom separates the muscles of gut and body wall. Based on nature of coelom animals are 3 types.

• Acoelomate: No coelom. The space between body wall and digestive cavity is filled with matrix (parenchyma). E.g. Poriferans to Platyhelminthes.

• Pseudocoelomate: Here, blastocoel becomes the coelom. It is not lined by peritoneal layer. E.g. Aschelminthes.

• Eucoelomate (True coelomate): Here, the coelom arises from the mesoderm. Coelom is lined by peritoneal layer and filled with coelomic fluid. E.g. Annelids to mammals.

• Haemocoelomates: In Arthropods and mollusks, true coelom is reduced and filled with blood.

Functions of coelom:

• It accommodates visceral organs. Coelomic fluid gives moist environment to visceral organs. Thus, friction is minimized.

• Acts as shock absorber.

Metamerism (segmentation)

• In some animals, the body is formed of similar parts (segments or metameres). This segmentation is called metamerism. E.g. Annelids, Arthropods.

• In vertebrates: only internal metamerism.

Notochord

• It is a supporting rod formed on the dorsal side during embryonic development in some animals. Animals with notochord are called chordates and those without notochord are called non-chordates.

CLASSIFICATION OF ANIMALS:

Phylum - Porifera

- Ex. Sponges.

• Marine, asymmetrical, cellular level of organization

• Have water canal system

• Ostia, Spongocoel, Osculum

• Choanocytes/ collar cells line in the spongocoel

• Digestion is intracellular

• Skeleton made up of spicules/ sponging fibres

• Hermaphrodite –male and female organs present on the same body.

• Reproduce asexually by fragmentation

• Sexually by gametes

• Fragmentation is internal and development is indirect

E.g. Sycon, Spongilla.

Phylum Coelenterata (Cnidaria)

- Ex. Hydra

• Aquatic / marine

• Sessile (fixed) / free swimming

• Radially symmetrical

• Have cnidoblasts / cnidocytes, stinging capsule on tentacles

• Used for defense, anchorage and to capture the prey

• Tissue level of organization diploblastic

• Mouth on hypostome.

• Digestion extracellular and intracellular

• Corals have skeleton made of calcium carbonate.

• Exhibit 2 basic forms called polyp and medusa.

• Polyp is sessile cylindrical (hydra)

• Medusa is umbrella shaped free living (jelly fish)

• They show alternation of generation (metagenesis) where polyp forms medusa asexually and medusa forms polyp sexually. Ex. Obelia

Ex. - Hydra, Physalia, Sea anemone, Sea pen, Sea fan, Brain coral

Phylum - Ctenophora (sea walnuts/comb jellies)

• Marine, radially symmetrical diploblastic

• Tissue level of organization

• Body bears 8 rows ciliated comb plates help in locomotion

• Digestion by intra and extra cellular

• Bioluminescence is well developed

• Sexes are not separate (monoecious)

• Reproduce by sexual reproduction

• Fertilization is external and indirect development.

Phylum – Platyhelminthes (flat worms)

• Dorso-ventrally flattened body

• Endoparasites, bilaterally symmetrical

• Organ level of organization

• Triploblastic - acoelomate

• Hooks and suckers are present

• Flame cells for excretions

• Sexes are not separate - fertilization is internal and development is through many larval stages

• Have high regeneration capacity

Phylum - Aschelminthes (round worms)

• Free living, aquatic, terrestrial parasitic

• Organ system level of body organization

• Bilaterally symmetrical and triploblastic

• Pseudocoelomate

• Digestive system is complete (mouth and anus)

• Sexes are separate (dioecious)

• Fertilization is internal and development is direct.

Ex. Ascaris, Wuchereria (filarial worm) and Ancylostoma (hookworm)

Phylum – Annelida (annulus little ring)

• Aquatic/terrestrial

• Free-living/ parasites

• Organ system level of body organization

• Bilaterally symmetrical

• Triploblastic

• Metamerically segmented – coelomate

• Metameres/body is segmented

• Marine Nereis possess parapodia

• Possess longitudinal and circular muscles help in locomotion

• Closed circulatory system

• Nephridia help in osmoregulation and excretion

• Dioecious (sexes are separate)

• Earthworm and leeches are monoecious

• Reproduction is sexual

E.g. Nereis, Pheretima (earth worm) and Hirudinaria (blood sucking leech)

Phylum – Arthropoda – (jointed legs)

• Largest phylum 2/3 are insects

• Organ system level of body organization

• Bilaterally symmetrical

• Segmented and coelomate

• Chitinous exoskeleton.

• Body has head thorax and abdomen.

• Have jointed appendages (organs for locomotion) respiratory organs are gills/book gills/Book lungs / tracheal system

• Open circulatory system.

• Sense organs are antennae, eye, statocysts (balance organs)

• Fertilization is internal.

• Excretion by malpighian tubules.

• Sexes are separate (Dioecious)

• Oviparous

• Development may be direct/ indirect

• Economic importance- Honey bees (Apis), Silkworm worm (Bombyx), Vectors. Mosquito, Housefly, Aquatic –crab, prawn, lobster

Phylum - Mollusca: (soft bodied and shelled)

• Second largest phylum

• Terrestrial and aquatic

• Organ system level of body organization

• Bilaterally symmetrical

• Triploblastic and Coelomate

• Calcareous shell and unsegmented body with head muscular foot and visceral hump

• Soft spongy layer of skin forms a mantle over the visceral hump

• Gills for respiration and excretion

• Head has sensory tentacles

• Mouth has file like rasping organ for feeding radula

• Sexes are separate (Dioecious)

• Oviparous

• Indirect development

E.g. Oyster, snail, squid, devil fish

Phylum - Echinodermata: (spiny skinned)

• Spiny skin has exoskeleton which is calcareous ossicles

• Marine organ level of body organization

• Radially symmetrical

• Coelomate

• Triploblastic

• Mouth of the lower side and anus on the upper side.

• Have water vascular system, help in locomotion, to capture and transport of food and for respiration

• Excretory system is absent

• Dioecious and fertilization is external, development is indirect with free swimming larva

Ex. Starfish, sea urchin, sea lily, sea cucumber

Phylum – Hermichordata

• Under non-chordate

• Worm like marine animals

• Organ system level of organization

• Bilaterally symmetrical, triploblstic

• Coclomate – body has anterior proboscis, a collar and a long trunk

• Circulatory system is open type

• Respiration is through gills

• Excretory organ is proboscis gland

• Sexes are separate

• Fertilization is external

• Development is indirect Ex. Balanoglossus

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Phylum – Chordata

• Presence of notochord dorsal hollow spinal cord –nerve cord and paired pharyngeal gill slits

• Bilaterally symmetrical and triploblastic

• Coelomate organ system level of organization

• Have post and tail

• Closed circulatory system

Chordata -Urochordata, Cephalochordate and Vertebrata

• Urochordata – notochord present in larval tail e.g. Ascidia, Salpa

• Cephalochordate – notochord extends from head to tail e.g. Amphioxus

Subphylum – Vertebrata:

• Possess notochord (replaced by vertebral column)

• All vertebrates are chordates but not all chordates are vertebrates (all vertebrates have vertebral column, but all chordates do not have vertebral chord).

• Fins and limbs for locomotion

Super class – Agnatha (without jaw) Class – Cyclostomata

• Ectoparasites on some fishes.

• Elongated body with 6-15 pairs of gill slits

• Sucking circular mouth without jaw

• Body is devoid of scales – paired fins

• Cranium and vertebral column are cartilaginous

• Circulation is closed –marine but migrate to fresh water for spawning

• After spawning they die

• Larvae, metamorphosis and return to the ocean

Super class - Gnathostomata (with jaw)

• Jaws are present

• Paired lateral appendages

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There are six classes:

Class – Chondrichthyes:

• Cartilage fish, endoskeleton is cartilage

• Body is stream lined

• Pelvic fins in male with claspers

• 5-7 pairs of gills.

• No operculum

• Mouth in ventral with teeth.

• Jaws are powerful

• Air bladder is absent

• Heart is 2 chambered (I auricle and one ventricle)

• Some possess electric /poison stings

• Poikilothermous (cold blooded)

• Body has placoid scales

• Unisexual

• Viviparous and fertilization is internal

Class – Osteichthyes - boney fish

• Endoskeleton is bone. Skin is covered by cycloid scales.

• Four pairs of gill slits with operculum, mouth is terminal, air bladder is present and help in buoyancy.

• Heart is two chambered (I auricle and I ventricle)

• Poikilotherms (cold blooded)

• Sexes are separate, fertilization is external and oviparous

Ex. Angel fish, Clown fish,

Class – Amphibia - dual life

• Live on land and move to water for breeding

• Body has head and trunk

• Tail is in larval stage – two pairs of limbs

• Digits without claws.

• Poikilotherms – eyes are with nictitating membranes

• Skin is smooth and moist with mucous glands

• Tympanum is ear drum

• Heart is three chambered (two auricles and one ventricle)

• Respiration by gills in larva and by lungs and skin in adults

• Digestive system complete

• Urinary tract and reproductive tract open in to a common cloacal chamber and the

• Opening is called cloacal aperture.

• Sexes are separate

• Oviparous

• Fertilization is external and development is indirect with tadpole larva Ex. Toad, Frog

Class – Reptilia

• Skin is dry without glands.

• Covered by horny epidermal scales (scutes)

• Tympanum is small no external opening

• 12 pairs of cranial nerves

• Trunk bears two pairs of pentadactyl limbs with claws.

• Heart with three and half chambered (two auricles, one which is incompletely partitioned ventricle)

• Only Crocodiles have four chambered heart

• Respiration is by lungs.

• Fertilization is internal.

• Oviparous and egg is covered by hard calcareous shells

Ex. Snake, Tortoise, Turtle, Viper, Lizard

Class-Aves​

• Forelimbs into wings and hind limbs modified for perching, swimming, running, etc.

• Voice box called syrinx is present

• Respiration is by lungs.

• Skin is dry with oil glands, at the base of tail.

• Bones are pneumatic bones (air cavities) helps to make the body light.

• Homeiothermous

• Heart is 4 chambered

• Oviparous and egg is with calcareous shells.

• Fertilization is internal.

Ex. Pigeon, Crow, Sparrow, Ostrich.

Class- Mammalia​

• Aquatic/aerial/terrestrial

• Body has head, neck, trunk and tail Have mammary glands in females’ External ear (pinna) is present

• Skin has sweat glands and sebaceous glands

• Heart is 4 chambered Respiration is by lungs. Body has hair

• Excretion is by kidneys (ureotelic – urea) Sexes are separate

• Viviparous (give birth young ones)

• Few are ovoviviparous – egg laying mammals (Platypus)

• Few are marsupials – pouched mammals with brood pouches (Kangaroo) Ex. Canis macaca, Camelus, Dolphin