Biology: Class 11 — Chapter 4: Animal Kingdom

• Cellular Level: Cells are arranged as loose cell aggregates. Division of labour occurs among cells. Example: Sponges (Porifera).
• Tissue Level: Cells performing the same function are arranged into tissues. Example: Coelenterates.
• Organ Level: Tissues are grouped together to form organs, each specialised for a particular function. Example: Platyhelminthes.
• Organ System Level: Organs associate to form functional systems, each concerned with a specific physiological function. Examples: Annelids, Arthropods, Molluscs, Echinoderms, and Chordates.
• Digestive System Patterns:
  • Incomplete: Has only a single opening to the outside of the body that serves as both mouth and anus (e.g., Platyhelminthes).
  • Complete: Has two distinct openings, a mouth and an anus.
• Circulatory System Patterns:
  • Open type: Blood is pumped out of the heart and cells/tissues are directly bathed in it.
  • Closed type: Blood is circulated through a series of vessels of varying diameters (arteries, veins, and capillaries).

• Asymmetrical: Any plane that passes through the centre does not divide the body into equal halves. Example: Most sponges.
• Radial Symmetry: Any plane passing through the central axis of the body divides the organism into two identical halves. Examples: Coelenterates, Ctenophores, and Echinoderms.
• Bilateral Symmetry: The body can be divided into identical left and right halves in only one plane. Examples: Annelids, Arthropods, etc.

• Diploblastic: Cells are arranged in two embryonic layers: an external ectoderm and an internal endoderm, with an undifferentiated layer called mesoglea in between. Example: Coelenterates.
• Triploblastic: Developing embryo has a third germinal layer, the mesoderm, in between the ectoderm and endoderm. Examples: Platyhelminthes to Chordates.

The presence or absence of a cavity between the body wall and the gut wall is key to classification.

• Coelomates: Possess a true body cavity (coelom) lined by mesoderm. Examples: Annelids, Molluscs, Arthropods, Echinoderms, Hemichordates, and Chordates.
• Pseudocoelomates: The body cavity is not lined by mesoderm; instead, mesoderm is present as scattered pouches. Example: Aschelminthes.
• Acoelomates: The body cavity is completely absent. Example: Platyhelminthes.

• Metamerism: External and internal division of the body into segments with serial repetition of at least some organs (e.g., Earthworm).
• Notochord: A mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals. Animals with a notochord are chordates; those without are non-chordates (Porifera to Echinoderms).

• Commonly known as sponges; mostly marine and asymmetrical.
• Exhibit cellular level of organisation.
• Water Transport/Canal System: Water enters through minute pores (ostia) into a central cavity (spongocoel) and exits through the osculum. Helps in food gathering, respiratory exchange, and waste removal.
• Lined by collar cells (choanocytes).
• Skeleton made of spicules or spongin fibres.
• Hermaphrodite; reproduce asexually by fragmentation and sexually by gametes. Fertilisation is internal with indirect development.
• Examples: Sycon (Scypha), Spongilla (Fresh water sponge), and Euspongia (Bath sponge).

• Aquatic, mostly marine, sessile or free-swimming, radially symmetrical.
• Possess stinging capsules or cnidoblasts (cnidocytes) on tentacles for anchorage, defense, and prey capture.
• Tissue level of organisation; diploblastic.
• Central gastro-vascular cavity with a single opening (mouth on hypostome).
• Two basic body forms:
  • Polyp: Sessile and cylindrical (e.g., Hydra, Adamsia).
  • Medusa: Umbrella-shaped and free-swimming (e.g., Aurelia / jelly fish).
• Metagenesis (Alternation of generation): Polyps produce medusae asexually, and medusae form polyps sexually (e.g., Obelia).
• Examples: Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan), and Meandrina (Brain coral).

• Commonly known as sea walnuts or comb jellies; exclusively marine, radially symmetrical, diploblastic.
• Body bears eight external rows of ciliated comb plates for locomotion.
• Exhibit prominent bioluminescence (emission of light).
• Sexes are not separate; reproduction is exclusively sexual. Fertilisation is external with indirect development.
• Examples: Pleurobrachia and Ctenoplana.

• Dorso-ventrally flattened body, commonly called flatworms.
• Mostly endoparasites; bilaterally symmetrical, triploblastic, acoelomate with organ level of organisation.
• Possess hooks and suckers in parasitic forms.
• Specialised flame cells help in osmoregulation and excretion.
• Sexes are not separate; fertilisation is internal with many larval stages. High regeneration capacity in Planaria.
• Examples: Taenia (Tapeworm), Fasciola (Liver fluke).

• Circular in cross-section, commonly called roundworms.
• Organ-system level, bilaterally symmetrical, triploblastic, and pseudocoelomate.
• Alimentary canal is complete with a well-developed muscular pharynx.
• Sexes are separate (dioecious); females are often longer than males.
• Examples: Ascaris (Roundworm), Wuchereria (Filaria worm), Ancylostoma (Hookworm).

• Aquatic or terrestrial; free-living or parasitic.
• Organ-system level, bilateral symmetry, triploblastic, metamerically segmented, and coelomate.
• Body surface marked into segments or metameres.
• Possess longitudinal and circular muscles for locomotion. Aquatic forms like Nereis have lateral appendages called parapodia for swimming.
• Excretory organs are nephridia.
• Examples: Nereis (dioecious), Pheretima (Earthworm - monoecious), and Hirudinaria (Blood sucking leech - monoecious).

• The largest phylum of Animalia, including insects (over two-thirds of all named species).
• Organ-system level, bilateral symmetry, triploblastic, segmented, and coelomate.
• Body covered by a chitinous exoskeleton; divided into head, thorax, and abdomen.
• Possess jointed appendages.
• Respiratory organs: gills, book gills, book lungs, or tracheal system.
• Circulatory system is of open type. Excretion via malpighian tubules.
• Mostly dioecious, internal fertilisation, mostly oviparous.
• Examples:
  • Economically important: Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect).
  • Vectors: Anopheles, Culex, and Aedes mosquitoes.
  • Living fossil: Limulus (King crab).

• The second largest animal phylum; terrestrial or aquatic.
• Organ-system level, bilateral symmetry, triploblastic, and coelomate.
• Body covered by a calcareous shell; unsegmented with a distinct head, muscular foot, and visceral hump.
• A soft, spongy layer of skin forms a mantle over the visceral hump. The space between them is the mantle cavity, containing feather-like gills.
• Mouth contains a file-like rasping organ for feeding called radula.
• Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Octopus (Devil fish).

• Spiny-bodied animals with an endoskeleton of calcareous ossicles; exclusively marine.
• Adults are radially symmetrical, but larvae are bilaterally symmetrical. Triploblastic and coelomate.
• Most distinctive feature: water vascular system, which helps in locomotion, capture/transport of food, and respiration.
• Excretory system is absent. Sexes are separate; fertilisation is external.
• Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea lily), Ophiura (Brittle star).

• Worm-like marine animals; earlier treated as a sub-phylum of Chordata.
• Have a rudimentary structure in the collar region called stomochord.
• Cylindrical body composed of an anterior proboscis, a collar, and a long trunk.
• Open circulatory system; respiration through gills; excretion via proboscis gland.
• Examples: Balanoglossus and Saccoglossus.

• Urochordata (Tunicata): Notochord present only in larval tail. Examples: Ascidia, Salpa, Doliolum.
• Cephalochordata: Notochord extends from head to tail and is persistent throughout life. Example: Branchiostoma (Amphioxus or Lancelet).
• Vertebrata: Possess notochord during embryonic period; replaced by a cartilaginous or bony vertebral column in adults. "All vertebrates are chordates but all chordates are not vertebrates."

• Ectoparasites on some fishes; jawless (Agnatha).
• Elongated body with 6-15 pairs of gill slits. Sucking and circular mouth without jaws.
• Devoid of scales and paired fins. Cranium and vertebral column are cartilaginous.
• Marine but migrate to fresh water for spawning, after which they die. Larvae return to the ocean after metamorphosis.
• Examples: Petromyzon (Lamprey) and Myxine (Hagfish).

• Marine animals with streamlined bodies and a cartilaginous endoskeleton.
• Notochord is persistent throughout life. Gill slits are separate and lack an operculum (gill cover).
• Skin contains tough, minute placoid scales. Teeth are modified placoid scales.
• Air bladder is absent; must swim constantly to avoid sinking.
• Cold-blooded (poikilothermous). Heart is two-chambered.
• Some possess electric organs (e.g., Torpedo) or poison stings (e.g., Trygon).
• Examples: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark).

• Marine and fresh water fishes with a bony endoskeleton.
• Four pairs of gills covered by an operculum on each side.
• Skin covered with cycloid/ctenoid scales.
• Air bladder is present, which regulates buoyancy.
• Heart is two-chambered; cold-blooded. Mostly oviparous with direct development.
• Examples: Exocoetus (Flying fish), Hippocampus (Sea horse), Labeo (Rohu), Catla (Katla).

• Can live in both aquatic and terrestrial habitats. Most have two pairs of limbs.
• Body divisible into head and trunk; skin is moist and lacks scales.
• A tympanum represents the ear.
• Alimentary, urinary, and reproductive tracts open into a common chamber called cloaca.
• Respiration by gills, lungs, and skin. Heart is three-chambered (two auricles, one ventricle).
• Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander).

• Creeping or crawling mode of locomotion. Mostly terrestrial.
• Body covered by dry and cornified skin, epidermal scales, or scutes.
• Tympanum represents ear. Limbs, when present, are two pairs.
• Heart is usually three-chambered, but four-chambered in crocodiles.
• Poikilotherms. Snakes and lizards shed scales as skin cast.
• Examples: Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Crocodilus (Crocodile), Naja (Cobra).

• Presence of feathers; most can fly (except flightless birds like Ostrich).
• Possess a beak. Forelimbs are modified into wings. Hind limbs adapted for walking, swimming, or perching.
• Long bones are hollow with air cavities (pneumatic bones).
• Digestive tract has additional chambers: the crop and gizzard.
• Heart is completely four-chambered. Warm-blooded (homoiothermous) animals.
• Respiration by lungs; air sacs supplement respiration.
• Examples: Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich).

• Found in diverse habitats. Unique feature: presence of milk-producing mammary glands.
• Skin possesses hair. External ears or pinnae are present.
• Different types of teeth are present in the jaw (thecodont, heterodont).
• Heart is four-chambered; homoiothermous. Respiration by lungs.
• Mostly viviparous with direct development.
• Examples:
  • Oviparous: Ornithorhynchus (Platypus).
  • Viviparous: Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Panthera tigris (Tiger).