Animal Kingdom NEET 2026

Cheatsheet Content

1. Basis of Classification Levels of Organization: Protoplasmic: (e.g., Protozoa - not in Animalia) Cellular: Porifera (sponges) Tissue: Coelenterata (Cnidaria), Ctenophora Organ: Platyhelminthes (flatworms) Organ-system: Aschelminthes to Chordata Symmetry: Asymmetrical: Porifera (some) Radial: Coelenterata, Ctenophora, Echinodermata (adults) Bilateral: Platyhelminthes to Chordata (most) Germ Layers: Diploblastic: Ectoderm & Endoderm (Porifera, Coelenterata, Ctenophora) Triploblastic: Ectoderm, Mesoderm & Endoderm (Platyhelminthes to Chordata) Coelom: (Body cavity lined by mesoderm) Acoelomate: No true coelom (Porifera, Cnidaria, Ctenophora, Platyhelminthes) Pseudocoelomate: Coelom not lined by mesoderm (Aschelminthes/Nematoda) Coelomate (Eucoelomate): True coelom (Annelida to Chordata) Segmentation: Metamerism: Body externally and internally divided into segments (Annelida, Arthropoda, Chordata) Notochord: Rod-like structure dorsal to gut, ventral to nerve cord. Non-chordates: Absent Chordates: Present (at least at some stage) 2. Phylum Porifera (Sponges) Level: Cellular Symmetry: Mostly asymmetrical Germ Layers: Diploblastic (no distinct germ layers, but two layers of cells) Coelom: Acoelomate Key Features: Water canal system (spongocoel, ostia, osculum, choanocytes/collar cells) Intracellular digestion Spicules/spongin fibers for support Hermaphrodite, asexual (fragmentation), sexual (gametes) Indirect development (larval stage) Examples: Sycon (Scypha), Spongilla (freshwater sponge), Euspongia (bath sponge) 3. Phylum Coelenterata (Cnidaria) Level: Tissue Symmetry: Radial Germ Layers: Diploblastic Coelom: Acoelomate Key Features: Cnidoblasts/cnidocytes (stinging cells) with nematocysts Gastro-vascular cavity (coelenteron) with single opening (mouth/anus) Digestion extracellular & intracellular Polyp (sessile, cylindrical) & Medusa (free-swimming, umbrella-shaped) forms Metagenesis (alternation of generation): Polyp produces medusae asexually, medusae form polyps sexually (e.g., Obelia ) Examples: Hydra , Adamsia (sea anemone), Physalia (Portuguese man-of-war), Aurelia (jellyfish), Corals 4. Phylum Ctenophora (Comb Jellies/Sea Walnuts) Level: Tissue Symmetry: Radial Germ Layers: Diploblastic Coelom: Acoelomate Key Features: Eight rows of ciliated comb plates for locomotion Bioluminescence (light emission) is well-marked Digestion extracellular & intracellular Hermaphrodite, sexual reproduction only, indirect development Examples: Pleurobrachia , Ctenoplana 5. Phylum Platyhelminthes (Flatworms) Level: Organ Symmetry: Bilateral Germ Layers: Triploblastic Coelom: Acoelomate Key Features: Dorso-ventrally flattened body Hooks & suckers in parasitic forms Flame cells (protonephridia) for osmoregulation & excretion Hermaphrodite, internal fertilization, indirect development (many larval stages) High regeneration capacity (e.g., Planaria ) Examples: Taenia solium (tapeworm), Fasciola hepatica (liver fluke), Planaria 6. Phylum Aschelminthes (Nematoda/Roundworms) Level: Organ-system Symmetry: Bilateral Germ Layers: Triploblastic Coelom: Pseudocoelomate Key Features: Circular in cross-section Complete digestive tract (muscular pharynx) Separate sexes (dioecious), often sexual dimorphism (females longer) Internal fertilization, direct or indirect development Examples: Ascaris (roundworm), Wuchereria (filarial worm), Ancylostoma (hookworm) 7. Phylum Annelida (Segmented Worms) Level: Organ-system Symmetry: Bilateral Germ Layers: Triploblastic Coelom: Coelomate (true coelom) Key Features: Metamerically segmented body Longitudinal & circular muscles for locomotion Closed circulatory system Nephridia for osmoregulation & excretion Neural system (paired ganglia, double ventral nerve cord) Dioecious or monoecious, sexual reproduction Examples: Nereis (marine, dioecious), Pheretima (earthworm, monoecious), Hirudinaria (blood-sucking leech, monoecious) 8. Phylum Arthropoda (Joint-footed Animals) Level: Organ-system Symmetry: Bilateral Germ Layers: Triploblastic Coelom: Coelomate (reduced, haemocoel present) Key Features: Largest phylum Chitinous exoskeleton Jointed appendages Body divided into head, thorax, abdomen (may be fused) Respiratory organs: Gills, book gills, book lungs, tracheal system Open circulatory system Excretion: Malpighian tubules Sensory organs: Antennae, eyes (compound & simple), statocysts Dioecious, internal fertilization, direct or indirect development Economically Important: Apis (honey bee), Bombyx (silkworm), Laccifer (lac insect) Vectors: Anopheles , Culex , Aedes (mosquitoes) Gregarious Pest: Locusta (locust) Living Fossil: Limulus (King crab) 9. Phylum Mollusca (Soft-bodied Animals) Level: Organ-system Symmetry: Bilateral Germ Layers: Triploblastic Coelom: Coelomate (reduced) Key Features: Second largest phylum Soft body often protected by calcareous shell Body divided into head, muscular foot, visceral hump (mantle) Mantle cavity contains feather-like gills (respiration & excretion) Radula (file-like rasping organ) for feeding Open circulatory system (except cephalopods) Dioecious, usually indirect development Examples: Pila (apple snail), Pinctada (pearl oyster), Sepia (cuttlefish), Loligo (squid), Octopus (devilfish), Aplysia (sea hare), Dentalium (tusk shell), Chaetopleura (chiton) 10. Phylum Echinodermata (Spiny-skinned Animals) Level: Organ-system Symmetry: Radial (adults), Bilateral (larvae) Germ Layers: Triploblastic Coelom: Coelomate Key Features: Calcareous ossicles as endoskeleton Water vascular system (ambulacral system) for locomotion, capture, respiration Complete digestive system (mouth ventral, anus dorsal) No excretory system Dioecious, external fertilization, indirect development (free-swimming larva) Remarkable power of regeneration Examples: Asterias (starfish), Echinus (sea urchin), Antedon (sea lily), Cucumaria (sea cucumber), Ophiura (brittle star) 11. Phylum Hemichordata (Half Chordates) Level: Organ-system Symmetry: Bilateral Germ Layers: Triploblastic Coelom: Coelomate Key Features: Worm-like marine animals Body divided into proboscis, collar, trunk Stomochord (a structure similar to notochord, but not true notochord) Open circulatory system Respiration by gills Excretion by proboscis gland Dioecious, external fertilization, indirect development Examples: Balanoglossus (tongue worm), Saccoglossus 12. Phylum Chordata Fundamental Features: Presence of a notochord Dorsal hollow nerve cord Pharyngeal gill slits Post-anal tail Divided into: Urochordata (Tunicata): Notochord only in larval tail. Body covered by tunic/test. (e.g., Ascidia , Salpa , Doliolum ) Cephalochordata: Notochord extends from head to tail, persistent throughout life. (e.g., Branchiostoma /Amphioxus/Lancelet) Vertebrata: Notochord replaced by cartilaginous or bony vertebral column in adults. Subphylum Vertebrata Classes: Class 1: Cyclostomata Jawless vertebrates (Agnatha) Ectoparasites on some fishes Elongated body, 6-15 pairs of gill slits Sucking and circular mouth without jaws Scaleless body, paired fins absent Cartilaginous cranium & vertebral column Closed circulation Marine, but migrate to freshwater for spawning, larvae return to ocean Examples: Petromyzon (lamprey), Myxine (hagfish) Class 2: Chondrichthyes (Cartilaginous Fishes) Marine, streamlined body Cartilaginous endoskeleton Ventral mouth Gill slits without operculum (gill cover) Skin with placoid scales; teeth are modified placoid scales (backwardly directed) Predaceous, powerful jaws No air bladder, so swim constantly to avoid sinking Poikilothermous (cold-blooded) Internal fertilization, viviparous (most) Examples: Scoliodon (dog fish), Pristis (saw fish), Carcharodon (great white shark), Trygon (sting ray - electric organ is absent, but has poison sting) Class 3: Osteichthyes (Bony Fishes) Marine & freshwater, streamlined body Bony endoskeleton Terminal mouth Four pairs of gills covered by operculum Cycloid/ctenoid scales Air bladder present (buoyancy) Poikilothermous External fertilization, oviparous, direct development Examples: Marine: Exocoetus (flying fish), Hippocampus (sea horse) Freshwater: Labeo (rohu), Catla (katla), Clarias (magur) Aquarium: Betta (fighting fish), Pterophyllum (angel fish) Class 4: Amphibia Aquatic & terrestrial habitats Body divisible into head & trunk (tail may be present) Skin moist without scales Two pairs of limbs Tympanum represents ear Alimentary canal, urinary, and reproductive tracts open into a common chamber called cloaca Respiration by gills, lungs, and skin Three-chambered heart (two atria, one ventricle) Poikilothermous Dioecious, external fertilization, oviparous, indirect development Examples: Bufo (toad), Rana (frog), Hyla (tree frog), Salamandra (salamander), Ichthyophis (limbless amphibia) Class 5: Reptilia (Creeping/Crawling Animals) Terrestrial animals, dry and cornified skin, epidermal scales/scutes No external ear openings (tympanum present) Limbs, if present, are two pairs Three-chambered heart (except crocodiles with 4-chambers) Poikilothermous Internal fertilization, oviparous, direct development Examples: Chelone (turtle), Testudo (tortoise), Chameleon (tree lizard), Calotes (garden lizard), Crocodilus (crocodile), Alligator , Hemidactylus (wall lizard) Snakes: Naja (cobra), Bungarus (krait), Vipera (viper) Class 6: Aves (Birds) Presence of feathers Most can fly (except flightless birds like ostrich) Beak present, no teeth Forelimbs modified into wings Hindlimbs adapted for walking, swimming, or clasping Dry skin without glands (except oil gland at tail base) Endoskeleton fully ossified (bony), long bones hollow (pneumatic) Air sacs connected to lungs (supplement respiration) Four-chambered heart Homoiothermous (warm-blooded) Internal fertilization, oviparous, direct development Examples: Corvus (crow), Columba (pigeon), Psittacula (parrot), Struthio (ostrich), Pavo (peacock), Aptenodytes (penguin), Neophron (vulture) Class 7: Mammalia Presence of mammary glands (milk production) Hair on body Two pairs of limbs (walking, running, climbing, burrowing, swimming, flying) External ears (pinnae) Different types of teeth in jaws (heterodonty) Four-chambered heart Homoiothermous Respiration by lungs Internal fertilization, viviparous (except Prototherians), direct development Examples: Oviparous: Ornithorhynchus (platypus) Viviparous: Macropus (kangaroo), Pteropus (flying fox), Camelus (camel), Macaca (monkey), Rattus (rat), Canis (dog), Felis (cat), Elephas (elephant), Equus (horse), Delphinus (common dolphin), Balaenoptera (blue whale), Homo sapiens (man)