Animal kingdom

• Animal Kingdom

  Over a million species of animals have been described, the need for classification becomes important to assign a systematic position to newly described species
• Basis of Classification

  • Fundamental features common to various individuals in relation to the arrangement of cells, body symmetry, nature of coelom, patterns of digestive, circulatory or reproductive systems
• Levels of Organisation

  • Cellular
  • Tissue
  • Organ
  • Organ system
• Incomplete digestive system


  Single opening to the outside of the body that serves as both mouth and anus
• Complete digestive system


  Two openings, mouth and anus
• Open circulatory system

  Blood is pumped out of the heart and the cells and tissues are directly bathed in it
• Closed circulatory system

  Blood is circulated through a series of vessels of varying diameters (arteries, veins and capillaries)
• Symmetry

  • Asymmetrical
  • Radial
  • Bilateral
• Diploblastic organisation

  Cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm
• Triploblastic organisation

  Developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm
• Coelom

  • Coelomate
  • Pseudocoelomate
  • Acoelomate
• Segmentation

  Body is externally and internally divided into segments with a serial repetition of at least some organs
• Notochord

  Mesodermally derived rod-like structure formed on the dorsal side during embryonic development
• Chordates

  Animals with notochord
• Non-chordates


  Animals which do not form notochord
• Porifera

  • Multicellular animals with cellular level of organisation
  • Water transport or canal system
  • Skeleton made up of spicules or spongin fibres
  • Sexes not separate, hermaphrodite
  • Reproduce asexually and sexually
• Coelenterata (Cnidaria)


  • Aquatic, mostly marine, sessile or free-swimming, radially symmetrical
  • Tissue level of organisation, diploblastic
  • Central gastro-vascular cavity with a single opening, mouth
  • Digestion extracellular and intracellular
  • Some have calcium carbonate skeleton
  • Exhibit polyp and medusa body forms
  • Alternation of generation (Metagenesis)
• Ctenophora

  • Exclusively marine, radially symmetrical, diploblastic
  • Tissue level of organisation
  • Body bears eight external rows of ciliated comb plates for locomotion
  • Digestion extracellular and intracellular
  • Bioluminescent
  • Sexes not separate, reproduction only sexual with external fertilisation and indirect development
• Platyhelminthes

  • Dorso-ventrally flattened body, bilaterally symmetrical, triploblastic, acoelomate
  • Organ level of organisation
  • Parasitic forms have hooks and suckers
  • Absorb nutrients directly through body surface
  • Flame cells for osmoregulation and excretion
  • Sexes not separate, internal fertilisation, indirect development with larval stages
  • Some have high regeneration capacity
• Aschelminthes

  • Body circular in cross-section, bilaterally symmetrical, triploblastic, pseudocoelomate
  • Organ-system level of body organisation
  • Complete alimentary canal with well-developed muscular pharynx
  • Excretory tube removes body wastes
  • Sexes separate (dioecious), internal fertilisation, development direct or indirect
• Annelida

  • Aquatic (marine and fresh water) or terrestrial, free-living, sometimes parasitic
  • Organ-system level of body organisation, bilateral symmetry, triploblastic, metamerically segmented, coelomate
  • Body surface distinctly marked into segments or metameres
  • Longitudinal and circular muscles for locomotion, aquatic forms have parapodia
  • Closed circulatory system, nephridia for osmoregulation and excretion
  • Neural system with paired ganglia and ventral nerve cord
  • Sexes separate (dioecious) or combined (monoecious), sexual reproduction
• Annelida


  • Organ-system level of body organisation
  • Bilateral symmetry
  • Triploblastic
  • Metamerically segmented
  • Coelomate
• Metameres


  Segments of the body
• Annelida


  • Longitudinal and circular muscles for locomotion
  • Closed circulatory system
  • Nephridia for osmoregulation and excretion
  • Paired ganglia connected by lateral nerves to a double ventral nerve cord
• Annelida


  • Nereis
  • Pheretima (Earthworm)
  • Hirudinaria (Blood sucking leech)
• Arthropoda

  • Largest phylum of Animalia
  • Organ-system level of organisation
  • Bilaterally symmetrical, triploblastic, segmented and coelomate
  • Body covered by chitinous exoskeleton
  • Body consists of head, thorax and abdomen
  • Jointed appendages
• Arthropoda respiratory organs


  • Gills
  • Book gills
  • Book lungs
  • Tracheal system
• Arthropoda


  • Open circulatory system
  • Sensory organs like antennae, eyes, statocysts
  • Excretion through malpighian tubules
  • Mostly dioecious with internal fertilisation and oviparous development
• Economically important insects

  • Apis (Honey bee)
  • Bombyx (Silkworm)
  • Laccifer (Lac insect)
• Arthropoda vectors

  • Anopheles
  • Culex
  • Aedes (Mosquitoes)
• Arthropoda gregarious pest


  • Locusta (Locust)
• Arthropoda living fossil


  • Limulus (King crab)
• Mollusca

  • Terrestrial or aquatic (marine or fresh water)
  • Organ-system level of organisation
  • Bilaterally symmetrical, triploblastic and coelomate
  • Body covered by calcareous shell and unsegmented with distinct head, muscular foot and visceral hump
  • Mantle covers visceral hump
  • Mantle cavity contains feather-like gills
  • Anterior head region has sensory tentacles
  • Mouth contains radula (file-like rasping organ)
• Echinodermata

  • Endoskeleton of calcareous ossicles
  • All marine with organ-system level of organisation
  • Adult radially symmetrical, larvae bilaterally symmetrical
  • Triploblastic and coelomate
  • Digestive system complete with mouth on ventral side and anus on dorsal side
  • Water vascular system for locomotion, food capture and transport, and respiration
  • No excretory system
  • Sexes separate, sexual reproduction with external fertilisation and indirect development
• Hemichordata

  • Worm-like marine animals with organ-system level of organisation
  • Bilaterally symmetrical, triploblastic and coelomate
  • Body with anterior proboscis, collar and long trunk
  • Open circulatory system
  • Respiration through gills
  • Excretion through proboscis gland
  • Sexes separate, external fertilisation and indirect development
• Hemichordata


  • Balanoglossus
  • Saccoglossus
• Chordata


  • Notochord, dorsal hollow nerve cord, paired pharyngeal gill slits
  • Bilaterally symmetrical, triploblastic, coelomate with organ-system level of organisation
  • Post-anal tail and closed circulatory system
• Chordata subphyla

  • Urochordata or Tunicata
  • Cephalochordata
  • Vertebrata
• Urochordata


  • Notochord only present in larval tail
• Cephalochordata


  • Notochord extends from head to tail, persistent throughout life