Short Notes Animal Kingdom - Short Notes for NEET

Basis of Classification

Phylum Porifera (Sponges)

• Features:
  • Cellular level of organization; asymmetrical
  • Aquatic (mostly marine), sessile
  • Body with pores (ostia) and canals (canal system)
  • Water current maintained by choanocytes (collar cells) with flagella
  • Central cavity: spongocoel; opening: osculum
  • Skeleton: spicules (calcareous/siliceous) or spongin fibers
  • Digestion: intracellular
  • Reproduction: asexual (budding, fragmentation, gemmules) and sexual
  • Hermaphrodite; development indirect (larva: amphiblastula or parenchymula)
  • Regeneration power high
• Examples: Sycon, Spongilla (freshwater), Euspongia (bath sponge)

Phylum Coelenterata (Cnidaria)

• Features:
  • Tissue level; radial symmetry; diploblastic
  • Aquatic (mostly marine)
  • Body forms: Polyp (sessile, cylindrical: Hydra, Adamsia) and Medusa (free-swimming, umbrella: Aurelia)
  • Cnidoblasts (cnidocytes): stinging cells with nematocysts on tentacles
  • Central gastrovascular cavity with single opening (mouth)
  • Digestion: extracellular and intracellular
  • Some show metagenesis (alternation of generations): polyp and medusa phases alternate
• Examples:
  • Hydra, Obelia (colonies)
  • Physalia (Portuguese man-of-war)
  • Aurelia (jellyfish)
  • Adamsia (sea anemone)
  • Pennatula (sea pen)
  • Corals: Gorgonia, Meandrina (brain coral)

Phylum Ctenophora

• Features:
  • Marine; biradial symmetry; diploblastic
  • Eight external rows of ciliated comb plates for locomotion
  • Colloblasts (adhesive cells) for prey capture (not cnidoblasts)
  • Bioluminescence present
  • Digestion: extracellular and intracellular
• Examples: Pleurobrachia (sea walnut), Ctenoplana

Phylum Platyhelminthes (Flatworms)

• Features:
  • Bilateral symmetry; triploblastic; acoelomate
  • Dorso-ventrally flattened body
  • Free-living (aquatic/terrestrial) or parasitic
  • Organ level of organization
  • Flame cells (protonephridia) for osmoregulation and excretion
  • No circulatory or respiratory system
  • Digestive system incomplete (anus absent) or absent in parasites
  • Hermaphrodite; fertilization internal
  • Parasites have complex life cycle with intermediate hosts
• Examples:
  • Planaria (free-living flatworm)
  • Fasciola (liver fluke - sheep liver parasite)
  • Taenia (tapeworm - intestinal parasite)

Phylum Aschelminthes (Nematoda - Roundworms)

• Features:
  • Bilateral symmetry; triploblastic; pseudocoelomate
  • Cylindrical, unsegmented body
  • Free-living (soil, water) or parasitic (plants, animals)
  • Digestive system complete (mouth to anus)
  • Excretory system with renette cells
  • Body covered with cuticle
  • Sexes separate (dioecious); often sexual dimorphism
  • Development may be direct or indirect
• Examples:
  • Ascaris (roundworm - intestinal parasite)
  • Wuchereria (filarial worm - causes filariasis/elephantiasis)
  • Ancylostoma (hookworm - causes anaemia)

Phylum Annelida (Segmented Worms)

• Features:
  • Bilateral symmetry; triploblastic; coelomate
  • Body metamerically segmented (with septa internally)
  • Aquatic (marine/freshwater) or terrestrial; free-living or parasitic
  • Locomotion by setae (chitinous lateral appendages) or parapodia (lateral paddle-like)
  • Complete digestive system
  • Closed circulatory system; blood with haemoglobin (red) or chlorocruorin (green)
  • Excretion by nephridia (segments)
  • Neural system: nerve ring + ventral nerve cord (ganglionated)
  • Hermaphrodite or dioecious; external or internal fertilization
  • Development direct or indirect (larva: trochophore)
• Examples:
  • Nereis (sandworm/ragworm - marine, parapodia)
  • Pheretima (earthworm - terrestrial, setae)
  • Hirudinaria (leech - ectoparasite, suckers)

Phylum Arthropoda (Largest Phylum)

• Features:
  • Bilateral symmetry; triploblastic; coelomate
  • Body segmented with jointed appendages (arthros = joint, poda = feet)
  • Body covered by chitinous exoskeleton; moulting (ecdysis) for growth
  • Body divided into head, thorax, and abdomen (or cephalothorax + abdomen)
  • Aquatic, terrestrial, or aerial; free-living or parasitic
  • Open circulatory system; blood = haemolymph
  • Respiration: gills (aquatic), book gills, book lungs, or tracheal system (terrestrial)
  • Excretion: Malpighian tubules, green glands, or coxal glands
  • Sensory organs: antennae, eyes (compound and simple), statocysts
  • Dioecious; fertilization mostly internal; development direct or indirect
• Examples:
  • Apis (honey bee), Musca (housefly), Anopheles (mosquito)
  • Bombyx (silkworm), Locusta (locust)
  • Palaemon (prawn), Cancer (crab)
  • Limulus (king crab), Palamnaeus (scorpion), Aranea (spider)

Phylum Mollusca (Second Largest Phylum)

• Features:
  • Bilateral symmetry; triploblastic; coelomate
  • Body unsegmented with distinct head, muscular foot, and visceral hump
  • Soft body covered by mantle; external calcareous shell (may be external, internal, or absent)
  • Aquatic (mostly marine) or terrestrial
  • Open circulatory system (except cephalopods - closed)
  • Respiration: gills (ctenidia), lungs, or mantle
  • Excretion: kidneys (metanephridia)
  • Digestive system with radula (rasping organ - except bivalves)
  • Nervous system: paired ganglia with nerve cords
  • Dioecious or hermaphrodite; development direct or indirect (larva: trochophore, veliger)
• Examples:
  • Pila (apple snail), Limax (slug)
  • Unio (freshwater mussel), Pinctada (pearl oyster)
  • Sepia (cuttlefish), Loligo (squid), Octopus

Phylum Echinodermata

• Features:
  • Adults: radial symmetry (pentamerous); Larvae: bilateral symmetry
  • Triploblastic; coelomate
  • Exclusively marine; free-living
  • Body covered with calcareous endoskeleton with spines
  • Water vascular system (ambulacral system): unique for locomotion, food capture, respiration
  • Tube feet: with suckers for locomotion
  • Digestive system complete
  • No excretory system; respiration by dermal branchiae, tube feet
  • Dioecious; external fertilization; development indirect (larva: bipinnaria, pluteus)
  • Regeneration power high
• Examples:
  • Asterias (starfish)
  • Ophiura (brittle star)
  • Echinus (sea urchin)
  • Cucumaria (sea cucumber)
  • Antedon (feather star)

Phylum Hemichordata

• Features:
  • Bilateral symmetry; triploblastic; coelomate
  • Marine, worm-like; cylindrical body
  • Body: proboscis, collar, and trunk
  • Stomochord (rudimentary notochord) in proboscis - connects hemichordates with chordates
  • Open circulatory system; respiration by gills
  • Excretion by glomerulus
  • Dioecious; external fertilization; indirect development (larva: tornaria - similar to echinoderm larvae)
• Examples: Balanoglossus (tongue worm), Saccoglossus

Phylum Chordata

• Fundamental Characteristics:
  • Notochord: rod-like structure along dorsal side (present at some stage of life)
  • Dorsal hollow nerve cord: single, tubular (becomes brain + spinal cord in vertebrates)
  • Paired pharyngeal gill slits: in pharynx (present at some stage; may be lost in adults)
  • Post-anal tail: extends beyond anus

Sub-phylum: Urochordata/Tunicata

• Features:
  • Marine; sessile adults, free-swimming larvae
  • Body covered with tunic/test (made of cellulose-like tunicin)
  • Notochord only in larval tail (hence Urochordata)
  • Larvae have all 4 chordate features; adults lose notochord, nerve cord, tail
  • Pharyngeal gill slits persist in adults
  • Retrogressive metamorphosis: larvae more advanced than adults
• Examples: Herdmania, Ascidia (sea squirt), Salpa

Sub-phylum: Cephalochordata

• Features:
  • Marine; small fish-like
  • Notochord extends from head to tail throughout life (hence Cephalochordata)
  • All 4 chordate features persist throughout life
  • No definite head
  • Circulatory system closed; respiration by gill slits
• Examples: Branchiostoma (Amphioxus/lancelet)

Sub-phylum: Vertebrata (Craniata)

• General Features:
  • Notochord replaced by vertebral column (backbone) made of vertebrae
  • Cranium (skull) protects brain
  • Paired appendages (fins or limbs)
  • Ventral heart (2, 3, or 4 chambered)
  • Kidneys for excretion and osmoregulation
  • Paired sensory organs

Class: Cyclostomata

• Features:
  • Jawless vertebrates (agnatha)
  • Elongated body; no scales
  • Circular sucking mouth without jaws
  • 6-15 pairs of gill slits for respiration
  • Marine; ectoparasites on fish
  • Notochord persists throughout life
  • Two-chambered heart
• Examples: Petromyzon (lamprey), Myxine (hagfish)

Class: Chondrichthyes (Cartilaginous Fish)

• Features:
  • Skeleton entirely cartilaginous
  • Marine; mostly predators
  • Body streamlined; ventral mouth
  • Skin with placoid scales (dermal denticles)
  • 5-7 pairs of gill slits without operculum
  • No swim bladder (air sac); buoyancy by oily liver
  • Two-chambered heart
  • Poikilothermous (cold-blooded)
  • Sexes separate; internal fertilization; mostly viviparous (some oviparous)
  • No larval stage
• Examples:
  • Scoliodon (dogfish)
  • Carcharodon (great white shark)
  • Trygon (stingray)
  • Torpedo (electric ray)
  • Pristis (saw fish)

Class: Osteichthyes (Bony Fish)

• Features:
  • Skeleton bony (ossified)
  • Marine or freshwater
  • Body streamlined; terminal or superior mouth
  • Skin with cycloid/ctenoid scales
  • Gills covered by operculum (gill cover)
  • Swim bladder (air bladder) for buoyancy
  • Two-chambered heart
  • Poikilothermous
  • Sexes separate; external fertilization; mostly oviparous
  • Development direct or indirect
• Examples:
  • Labeo (rohu), Catla (katla)
  • Clarias (catfish - air breathing)
  • Hippocampus (sea horse)
  • Exocoetus (flying fish)
  • Anabas (climbing perch)

Class: Amphibia

• Features:
  • Dual life: aquatic larva, terrestrial adult (amphi = both, bios = life)
  • Body divisible into head and trunk (tail may be present)
  • Skin moist, glandular; no scales
  • Two pairs of pentadactyl limbs (some limbless)
  • Respiration: gills (larvae), lungs and skin (adults)
  • Three-chambered heart (two atria + one ventricle)
  • Poikilothermous
  • Dioecious; external fertilization; oviparous
  • Indirect development with metamorphosis (tadpole larva)
  • Can undergo aestivation (summer sleep) and hibernation (winter sleep)
• Examples:
  • Rana (frog), Hyla (tree frog)
  • Bufo (toad)
  • Salamandra (salamander)
  • Ichthyophis (limbless amphibian)

Class: Reptilia

• Features:
  • Terrestrial or aquatic; creeping/crawling mode of locomotion
  • Body covered with dry, cornified skin with epidermal scales/scutes
  • Body divisible into head, neck, trunk, and tail
  • Usually two pairs of pentadactyl limbs (absent in snakes)
  • Respiration by lungs only
  • Three-chambered heart (except crocodiles: four-chambered)
  • Poikilothermous
  • Dioecious; internal fertilization; mostly oviparous
  • Eggs with tough leathery shell (cleidoic eggs)
  • Direct development; no metamorphosis
• Examples:
  • Chelone (turtle), Testudo (tortoise)
  • Hemidactylus (wall lizard), Chameleon
  • Calotes (garden lizard), Draco (flying lizard)
  • Crocodilus (crocodile), Alligator
  • Naja (cobra), Viper, Krait

Class: Aves (Birds)

• Features:
  • Body covered with feathers (unique to birds)
  • Forelimbs modified into wings for flight
  • Hind limbs for walking, perching; with scales
  • Beak without teeth; pneumatic bones (hollow, air-filled for light weight)
  • Streamlined body; air sacs connected to lungs
  • Respiration by lungs
  • Four-chambered heart
  • Homeothermic (warm-blooded)
  • Dioecious; internal fertilization; oviparous
  • Hard-shelled eggs; direct development
  • High metabolic rate; 12th cranial nerve present
• Examples:
  • Corvus (crow), Columba (pigeon)
  • Psittacula (parrot), Pavo (peacock)
  • Struthio (ostrich - flightless)
  • Neophron (vulture)

Class: Mammalia

• Features:
  • Body covered with hair/fur
  • Mammary glands present (for milk production to nourish young)
  • Pinnae (external ears) present
  • Two pairs of limbs for walking, running, climbing, burrowing, swimming
  • Teeth embedded in sockets (thecodont); different types (heterodont); replaced once (diphyodont)
  • Skin with sweat and sebaceous (oil) glands
  • Four-chambered heart
  • Respiration by lungs
  • Homeothermic
  • Dioecious; internal fertilization; viviparous (except monotremes)
  • Direct development
  • Diaphragm present (separates thorax and abdomen)
• Examples:
  • Oviparous mammals: Ornithorhynchus (platypus), Echidna (spiny anteater)
  • Marsupials (with pouch/marsupium): Macropus (kangaroo)
  • Placental mammals:
    • Rattus (rat), Mus (mouse)
    • Canis (dog), Felis (cat)
    • Elephas (elephant)
    • Equus (horse)
    • Panthera (lion, tiger, leopard)
    • Balaenoptera (blue whale)
    • Homo sapiens (human)