Introduction to Animal Diversity

Biology 1108 Lecture Notes

Chapter 27: Introduction to Animal Diversity

Kingdom Animalia

  • Fundamental Characteristics of Animals:

    • Eukaryotic

    • Multicellular

    • Heterotrophic (organisms that cannot produce their own food and must obtain it by consuming other organisms)

    • No cell walls, which distinguishes them from plants and fungi

    • Body Symmetry:

    • Invertebrates: Animals without backbones (vertebral columns)

    • Vertebrates: Animals with backbones (vertebral columns)

    • Body Symmetry Types:

      • Asymmetry

      • Radial Symmetry

      • Bilateral Symmetry

Animal Phylogeny

  • Cladogram of Major Animal Phyla:

    • Porifera (sponges)

    • Cnidaria (jellyfish, corals)

    • Platyhelminthes (flatworms)

    • Nematoda (roundworms)

    • Mollusca (snails, clams)

    • Annelida (segmented worms)

    • Arthropoda (insects, crustaceans)

    • Echinodermata (starfish, sea urchins)

    • Chordata (vertebrates, including mammals)

  • Body Plans and Symmetries:

    • Radial Symmetry: Exhibited by Cnidaria and Ctenophora

    • Bilateral Symmetry: Found in several phyla including Arthropoda and Chordata

    • Pseudocoelom: Identified in certain groups like Nematoda

    • Coelom: Defined as a body cavity lined with mesoderm; associated with more complex body structures

Major Variations in Body Plan

  1. Presence of Tissue Layers:

    • Parazoans: Sponges which contain no true tissue layers

    • Eumetazoans: All other animals with true tissues

  2. Body Symmetry:

    • Diploblastic: Organisms such as Cnidaria and Ctenophora with two germ layers.

    • Triploblastic: Organisms with three germ layers include most other animal phyla.

  3. Body Cavities (Coelom):

    • Acoelomates: No body cavity (e.g., flatworms)

    • Pseudocoelomates: Body cavity not a true coelom, partially lined with mesoderm (e.g., roundworms)

    • Coelomates (Eucoelomates): True coelom body cavity completely lined with mesoderm (e.g., annelids, molluscs)

Germ Layers

  • Definitions and Functions of Germ Layers:

    1. Ectoderm: The outermost layer, primarily forms skin and nervous system

    2. Mesoderm: The middle layer, forms muscles and connective tissues

    3. Endoderm: The innermost layer, forms the digestive tract

  • Diploblastic Organisms:

    • Possess only the ectoderm and endoderm

    • Example: Phylum Cnidaria

  • Triploblastic Organisms:

    • Bodies organized from all three layers: ectoderm, mesoderm, and endoderm

    • Example: most other higher animal phyla (e.g., chordates, arthropods)

Body Cavity Classification

  • Classification of Organisms Relative to Body Cavities:

    1. Acoelomates: No central body cavity

    2. Pseudocoelomates: Have a body cavity known as pseudocoel which is derived from blasted and mesoderm

    3. Coelomates: Have a body cavity (coelom) fully lined with mesodermal tissue

  • Coelom Formation Mechanisms:

    • Schizocoelous: formation of coelom by splitting of mesodermal bands (characteristic of protostomes)

    • Enterocoelous: formation involves folding of archenteron (characteristic of deuterostomes)

Major Developmental Patterns: Protostomes and Deuterostomes

  • Protostomes:

    • Spiral and determinate cleavage
      discusses early embryonic development where each cell has a predetermined fate

    • Blastopore develops into the mouth

    • Examples include Mollusca, Annelida, Arthropoda

  • Deuterostomes:

    • Radial and indeterminate cleavage with the potential for cellular differentiation

    • Blastopore develops into the anus

    • Examples include Echinodermata, Chordata

Summary of Major Clades within Kingdom Animalia

  • Metazoans:

    • Subdivided into:

    • Radiata: Includes phyla with radial symmetry (e.g., Cnidaria)

    • Bilateria: Includes bilaterally symmetrical organisms (most other animal existences)

      • Divided further into:

      • Protostomes: Lophotrochozoans and Ecdysozoans

      • Deuterostomes: includes Echinodermata and Chordata

This complex classification emphasizes that the diversity of animal life is underpinned by differences in body plans, germ layers, and developmental processes, which offers insight into animal evolution and physiology.