Introduction to Animal Diversity

Biology 130: Zoology - Introduction to Animal Diversity

Overview of Zoology

  • Course Title: Biology 130 Fall 2025: Zoology
  • Focus on animal diversity, structure, and function.
  • Recommended to bring textbook to labs for reference.

Instructor Background

  • Ph.D. in Zoology with a research background in functional morphology of archosaurs (dinosaurs, pterosaurs, birds, and ancestors).
  • Current research emphasis on reproductive biology and conservation of the Western pond turtle, Emys marmorata.

Fundamental Questions in Zoology

  • Key question: How do we define an animal?
  • Initial discussion on the characteristics of animals.

Phylogenetic Tree

  • Constructed by microbiologist Carl Woese based on genetic relationships.
  • Divides organisms into three domains:
    • Bacteria
    • Archaea
    • Eukarya
  • Bacteria and Archaea are prokaryotes (no nucleus or organelles).
  • LUCA (Last Universal Common Ancestor) is a crucial concept; represented on the phylogenetic tree.
Understanding LUCA
  • LUCA is theorized to be the common ancestor of all current forms of life.

Fossil Record and Eukaryotic Life

  • Oldest eukaryotic fossil: Grypania; however, biomarkers of eukaryotes date back to 2.7 billion years.
  • The Earth is approximately 4.6 billion years old; first life forms appeared around this time.

Definition of Animals

  • Animals are defined as:
    • Multicellular, heterotrophic eukaryotes (ingesting organic nutrients).
    • Lack cell walls, possessing structural proteins like collagen.
    • Have unique tissue types:
    • Nervous tissue
    • Muscle tissue
    • Dominant diploid stage (sexual reproduction).

Developmental Patterns in Animals

  • Fertilization: Formation of a diploid zygote (fertilization of haploid sperm and egg).
  • Development includes:
    • Cleavage: Mitotic divisions of the zygote.
    • Blastula Formation: Hollow ball of cells.
    • Gastrulation: Inward folding of the blastula forming germ layers.
    • Germ Layers: Endoderm, ectoderm (and possibly mesoderm).
Developmental Concepts
  • Larval Stages: Many animals go through distinct larval stages before metamorphosing into adults.
  • Direct vs. Indirect Development: Many organisms experience metamorphosis except sponges.

Homeobox Genes (HOX Genes)

  • Defined as “master control genes” found in all animals.
  • Initiate and coordinate developmental processes, specifying developmental timing and patterning.
  • HOX genes produce regulatory proteins and are critical for the body’s modular framework.
  • Highly conserved across animal kingdom; increased numbers correlate with complexity.

Animal Origins

  • Animals are a monophyletic group, all stemming from a common ancestor—a colonial flagellated ancestor (choanoflagellate) dating back over 700 million years.
  • Choanoflagellates were likely the ancestors of all animals based on genetic and morphological analyses.

Symmetry and Body Plans

  • Understanding body symmetry:
    • Asymmetrical: Example - Sponges
    • Radial symmetry: Examples - Jellyfish, corals
    • Bilateral symmetry: Examples - Humans and various other multicellular organisms.
Tissues and Germ Layers
  • Definition of tissues: Groups of cells performing specific functions.
  • Germ Layers: Endoderm (gut lining), Ectoderm (skin), Mesoderm (muscle and other tissues).
  • Animals can be classified as diploblastic (2 layers) or triploblastic (3 layers).

Evolutionary Relationships

  • Traditional Phylogenies: Based on anatomical and developmental characteristics, including fossils.
  • Molecular Biology: Incorporates genetic data leading to evolving phylogenetic hypotheses.
  • Importance of evolutionary trees to understand relationships and organization of animal life.
Major Groupings of Animals
  • Parazoa: Lack true tissues, sponges (Porifera) fall under this category.
  • Eumetazoa: Animals with true tissues, including various phyla:
    • Bilateria: Animals showing bilateral symmetry, which can be further divided into Protostomes and Deuterostomes.

Body Cavity Organization

  • Acoelomates: (flatworms) lack body cavity.
  • Pseudocoelomates: (nematodes) partial body cavity lining.
  • Coelomates: (annelids) body cavity entirely lined with mesoderm derived tissues.

Protostomes vs. Deuterostomes

  • Protostomes: Mouth develops first from the blastopore, exhibit spiral cleavage (e.g., mollusks, annelids, arthropods).
  • Deuterostomes: Anus develops first from the blastopore, exhibit radial cleavage (e.g., echinoderms, chordates).

Classes of Phylum Cnidaria

  • Defined by their cnidocytes (stinging cells); divided into classes such as Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa, each with unique features and life cycles.

Cnidarian Body Plan

  • Includes polymorphic forms (polyp and medusa) and digestive system known as the gastrovascular cavity, which functions in digestion and nutrient distribution through a simple flow.
Nerve and Muscle System in Cnidarians
  • Cnidarians have simple nerves and muscles, NOT true muscles (which derived from mesoderm).
  • Hydrostatic skeleton supports movement, utilizing a nerve net structure.

Cambrian Explosion

  • A remarkable period marking the rapid appearance of most modern animal phyla around 540 million years ago.
  • Possible causes include ecological shifts, increasing atmospheric oxygen levels, and evolution of HOX genes.

Key Takeaways

  • Significance of the Cambrian explosion in terms of diversification and evolutionary history.
  • Role of evolutionary relationships documented through both molecular and morphological data.
  • The complex relationships and lineage among different animal taxa elucidate modern animal traits and characteristics.