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General Biology: Animal Diversity and Evolution

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  • General characteristics of animals
    Animals are heterotrophic eukaryotes, multicellular, have tissues from embryonic layers, mostly reproduce sexually, and possess Hox developmental genes.
  • Kingdom of consumers
    Animals are efficient consumers with adaptations to detect, capture, eat, and digest other organisms, e.g., chameleons use a long, sticky tongue to catch insects.
  • Animal cell structure
    Animal cells lack cell walls and are supported by collagen. Unique tissues include nervous and muscle tissues.
  • Animal reproduction and development
    Most animals reproduce sexually with a dominant diploid stage. Fertilization leads to cleavage, forming a hollow blastula, which undergoes gastrulation to form embryonic tissue layers.
  • Hox genes
    Hox genes regulate body form development and are conserved across animals, enabling diverse morphologies.
  • Common ancestor of animals
    Animals likely evolved from protists called choanoflagellates, sharing genes for cell adhesion and signaling.
  • Cambrian explosion
    Occurred 535–525 million years ago, marking the rapid appearance of many animal phyla, especially bilaterians with bilateral symmetry and complete digestive tracts.
  • Animal body plans
    Body plans include symmetry types: radial symmetry (top and bottom, no left/right) and bilateral symmetry (distinct left/right, front/back).
  • Radial vs bilateral symmetry
    Radial animals are often sessile or planktonic (e.g., cnidarians), while bilateral animals are typically active movers with a central nervous system.
  • Germ layers in animals
    Animals develop from 3 germ layers: ectoderm (outer layer), endoderm (inner layer), and mesoderm (middle layer, only in bilaterians).
  • Diploblastic vs triploblastic
    Diploblastic animals have ectoderm and endoderm (e.g., cnidarians). Triploblastic animals have all three germ layers including mesoderm (all bilaterians).
  • Body cavities
    Most triploblastic animals have a body cavity called a coelom, derived from mesoderm, which cushions organs and allows independent movement.
  • Types of body cavities
    Coelomates have a true coelom, pseudocoelomates have a body cavity not fully lined by mesoderm, and acoelomates lack a body cavity.
  • Protostome vs deuterostome development
    Protostomes have spiral, determinate cleavage; mouth develops from blastopore. Deuterostomes have radial, indeterminate cleavage; anus develops from blastopore.
  • Cleavage types
    Protostomes exhibit spiral and determinate cleavage; deuterostomes exhibit radial and indeterminate cleavage.
  • Significance of indeterminate cleavage
    Indeterminate cleavage allows each early embryonic cell to develop into a complete embryo, enabling identical twins and embryonic stem cells.
  • Animal phylogeny key points
    All animals share a common ancestor; sponges are basal; eumetazoa have tissues; most animals are bilaterians; bilaterians include invertebrates and vertebrates.
  • Major animal clades
    Bilateria divides into three major clades: Lophotrochozoa, Ecdysozoa, and Deuterostomia.
  • Phylum Porifera
    Sponges lack true tissues and have choanocytes (collar cells) that ingest bacteria and tiny food particles.
  • Phylum Cnidaria
    Cnidarians are diploblastic, radially symmetrical, have nematocytes (stinging cells), and a gastrovascular cavity with one opening.
  • Phylum Platyhelminthes
    Flatworms are dorsoventrally flattened acoelomates with a gastrovascular cavity or no digestive tract.
  • Phylum Rotifera
    Rotifers are pseudocoelomates with an alimentary canal, jaws (trophi), and a head with a ciliated crown.
  • Phylum Mollusca
    Mollusks are coelomates with a muscular foot, visceral mass, mantle, reduced coelom, and most have a calcium carbonate shell.
  • Phylum Annelida
    Segmented worms with a segmented body wall and internal organs, except the digestive tract which is unsegmented.
  • Phylum Nematoda
    Roundworms are cylindrical pseudocoelomates with tapered ends, no circulatory system, and undergo ecdysis (molting).
  • Phylum Arthropoda
    Arthropods have segmented bodies, jointed appendages, and an exoskeleton made of protein and chitin.
  • Phylum Echinodermata
    Echinoderms have bilaterally symmetrical larvae, five-part adult body organization, a water vascular system, and an endoskeleton.
  • Phylum Chordata
    Chordates have a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.