IF

Invertebrate Diversity Notes

Evolution of Invertebrate Diversity Overview

  • The study of invertebrate diversity begins with the understanding of animal characteristics and classifications.

Defining Animals

  • Animals are characterized by the following features:
    • Eukaryotes: Organisms with complex cells containing a nucleus.
    • Multicellular Heterotrophs: They cannot produce their own food; they rely on ingestion.
    • Lack of Cell Walls: Unlike plant cells, animal cells do not have rigid walls.
    • Unique Life Cycles: Differentiated embryonic development stages include:
      • Haploid (n) and Diploid (2n) stages
      • Life stages: Egg → Zygote → Larva → Adult

Body Plans of Animals

  • Animals can be categorized based on their body plans, which exhibit:
    • Symmetry:
      • Radial Symmetry: Symmetry around a central axis (e.g., sea anemones).
      • Bilateral Symmetry: Divides the body into two mirror-image halves (e.g., lobster).
    • Presence of True Tissues: Distinction into groups based on the layers of tissues present:
      • Diploblastic: Two tissue layers (ectoderm and endoderm).
      • Triploblastic: Three tissue layers include mesoderm (e.g., coelomates).
    • Body Cavity: Animals can be classified as:
      • Coelomates: Organisms with a true body cavity lined by mesoderm.
      • Pseudocoelomates: Organisms with a body cavity not entirely lined by mesoderm.
      • Acoelomates: Organisms lacking a body cavity.
    • Embryonic Development:
      • Protostome Development: Mouth develops from the blastopore (e.g., mollusks).
      • Deuterostome Development: Anus develops from the blastopore (e.g., echinoderms, chordates).

Examples of Different Invertebrate Phyla

  • Sponges (Phylum Porifera):

    • Simple structure lacking true tissues and organs.
    • Filter feeders using choanocytes to draw water through their porous bodies.

  • Cnidarians (Phylum Cnidaria):

    • Exhibit radial symmetry with two tissue layers.
    • Possess stinging cells (cnidocytes) for capturing prey.
    • Body forms include polyp (e.g., hydra) and medusa (e.g., jellyfish).

  • Flatworms (Phylum Platyhelminthes):

    • Simplest bilateral animals lacking a body cavity (acoelomates).
    • Include free-living and parasitic forms, such as tapeworms.

  • Rotifers (Phylum Rotifera):

    • Microscopic, multicellular organisms with specialized organs.
    • Capable of parthenogenesis (female reproduction without male fertilization).

  • Molluscs (Phylum Mollusca):

    • Structured with a muscular foot, visceral mass, and mantle.
    • Includes various classes like gastropods (snails), bivalves (clams), and cephalopods (squid).
    • Many exhibit a trochophore larval stage.

Advanced Features of Animals

  • Differentiation in circulatory systems, organ structures, and sensory capabilities among different groups, emphasizing the evolutionary adaptations in response to diverse environmental conditions.
  • Special adaptations like the lophophore in lophophorates for feeding through suspension feeding.