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๐Ÿ“– Summaries โ€บ Zoology

Animal Kingdom

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Animal Kingdom

With over a million animal species described, classification is essential. Animals are classified using fundamental features common to many individuals.

Basis of classification

  • Levels of organisation: cellular (sponges) - tissue (coelenterates, ctenophores) - organ (platyhelminthes) - organ system (aschelminthes onward).
  • Symmetry: asymmetrical (sponges), radial (coelenterates, ctenophores, adult echinoderms), bilateral (annelids to chordates).
  • Germ layers: diploblastic (two layers + mesoglea, e.g. coelenterates) vs triploblastic (mesoderm present, platyhelminthes to chordates).
  • Coelom: acoelomate (no cavity, platyhelminthes), pseudocoelomate (aschelminthes), coelomate (mesoderm-lined cavity, annelids onward).
  • Segmentation (metamerism): serial body segments, first clearly seen in annelids.
  • Notochord: present in chordates; non-chordates (porifera to echinoderms) lack it.

Non-chordate phyla

Porifera (sponges, canal system, choanocytes), Coelenterata/Cnidaria (cnidoblasts, polyp & medusa), Ctenophora (comb plates, bioluminescence), Platyhelminthes (flatworms, flame cells), Aschelminthes (roundworms, pseudocoelom), Annelida (segmented, nephridia, closed system), Arthropoda (largest phylum, jointed appendages, malpighian tubules), Mollusca (shell, mantle, radula), Echinodermata (water vascular system, spiny skin), Hemichordata (proboscis-collar-trunk, stomochord).

Chordata

Defined by a notochord, dorsal hollow nerve cord, paired pharyngeal gill slits, post-anal tail and closed circulatory system. Subphyla: Urochordata, Cephalochordata (protochordates) and Vertebrata. All vertebrates are chordates, but all chordates are not vertebrates.

Vertebrate classes

Cyclostomata (jawless ectoparasites), Chondrichthyes (cartilaginous fishes), Osteichthyes (bony fishes), Amphibia, Reptilia, Aves and Mammalia. Heart chambers rise from two (fishes) to three (amphibians, most reptiles) to four (crocodiles, aves, mammals). Fishes, amphibians and reptiles are cold-blooded; aves and mammals are warm-blooded. Mammals are unique in having mammary glands and hair.