Biology

Animal Kingdom

Animal Kingdom
Animals are multicellular, eukaryotic organisms. Most of them consume organic material, breathe oxygen, are able to move, can reproduce sexually.
Classification of Animals
• Based on level of organization
 Cellular level – the cells are arranged as loose cell aggregates. e.g. sponges
 Tissue level – cells performing the same function are arranged into tissues. e.g. coelenterates
 Organ level – tissues are grouped together to form organs. e.g. platyhelminthes
 Organ system level – Organs have associated to form functional systems. e.g. Annelids, Arthropods, Molluscs
• Based on Symmetry
 Radial – any plane passing through the central axis of the body divides it into two identical halves. e.g. coelenterates, ctenophores and echinoderms
 Bilateral – the body can be divided into identical left and right halves in only one plane. e.g. annelids, arthropods
• Based on Diploblastic and Triploblastic Organisation
 Diploblastic – cells are arranged in two embryonic layers ectoderm and endoderm. e.g. coelenterates
 Triploblastic – the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm. e.g. platyhelminthes, chordates
• Based on Coelom (body cavity, which is lined by mesoderm)
 Body cavity is absent and are called acoelomates. e.g. platyhelminthes
 Animals possessing coelom and are called coelomates. e.g. annelids, molluscs, arthropods, chordates etc.
 Animals possessing the mesoderm as scattered pouches in between the ectoderm and endoderm and are called pseudocoelomates.
• Based on Segmentation
 the body is externally and internally divided into segments with a serial repetition of at least some organs. e.g. earthworm
• Based on Notochord (mesodermally derived rod-like structure formed on the dorsal side during embryonic development)
 Animals with notochord are called chordates
 Animals without notochord are called non-chordates e.g. porifera

 Phylums
• Porifera (sponges)
 Asymmetrical
 Cellular level of organization
 They are hermaphrodite (having both male and female sex organs)
 e.g. spongilla
• Coelenterata (Cnidaria)
 mostly marine, immobile or free-swimming
 Radially symmetrical
 e.g. physalia
• Ctenophora (sea walnuts or comb jellies)
 Marine
 Radically symmetrical
 Diploblastic
 Tissue level of organization
 Emit light
 Comb plates helps in moving
 Sexes not separate
• Platyhelminthes (flatworms)
 flattened body back to front
 mostly endoparasites (a parasite that lives inside its hosts)
 triploblastic and acoelomate
• Aschelminthes
 Circular
 Organ system level of body organization
 bilaterally symmetrica
 triploblastic
 e.g. ascaris (roundworm)
• Annelida
 Acquatic or terrestrial
 Organ system level of organization
 Bilateral symmetry
 Triploblastic

• Arthropoda
 Largest phylum of Animalia
 Insects come under Arthropoda
 Organ system level of organization
 e.g. Apis (honey bee)
• Mollusca
 Second largest phylum of Animalia
 Bilaterally symmetric
 Triploblastic
 e.g. Octopus
• Echinodermata
 Marine
 Organ level of organization
 Symmetrical
 Triploblastic
 Presence of water vascular system
• Hemichordata
 Marine
 Organ system level of organization
 Bilaterally symmetrical
 Triploblastic
• Chordata
 Presence of notochord
 Bilaterally symmetrical
 Triploblastic
 Organ system level of organization
 3 subphyla are Urochordata, Tunicata, Cephalochordata and Vertebrata
Vertebrata
• Agnatha (jawless)
 Cyclostomata
• Gnathostomata (have jaw)
 Pisces (have fins) – Chondrichthyes and Osteichthyes
 Tetrapoda (have limbs) – Amphibia, Reptelia, Aves and Mammals