Animal Taxonomy and Classification

Introduction

• Animal taxonomy involves identifying, naming, and classifying animals.
• Carolus Linnaeus (1707-1778) is recognized as the founder of taxonomy.
• There are approximately 1.2 million identified animal species, with estimates of 9-10 million total species on Earth.
• The importance of classification lies in assigning a systematic position to newly discovered species.

Taxonomy vs. Systematics

• Taxonomy focuses on describing, naming, and classifying organisms.
• Systematics studies biological diversity and evolutionary relationships between organisms.
• Taxonomic groups are now based on hypotheses about evolutionary relationships derived from systematics.

Classification

• The classification of animals is hierarchical, with progressively smaller and more specific groups within each level.
• For example, a species of nematode, Caenorhabditis elegans, is classified as follows:
  • Kingdom: Animalia
  • Phylum: Nematoda
  • Class: Chromadorea
  • Order: Rhabditida
  • Family: Rhabditidae
  • Genus: Caenorhabditis
  • Species: elegans

Body Symmetry

• Body symmetry refers to the balance of an organism's body parts.
• Three axes are considered:
  • Anterior-posterior (head-tail) axis
  • Dorsal-ventral (back-belly) axis
  • Left-right axis
• Cross sections bisecting the anterior-posterior axis are used to categorize symmetry:
  • Bilateral symmetry: A single plane divides the body into two mirror images.
  • Radial symmetry: Many planes can divide the body equally.
  • Asymmetry: No plane can divide the body into equal halves.

Coelom

• A coelom is a body cavity present in most animals, located between the intestinal canal and the body wall.
• The presence of body cavities plays a role in classification.

Germ Layers

• Germ layers are the primary tissues that form during embryonic development.
• Diploblastic animals: Have two embryonic layers:
  • External ectoderm
  • Internal endoderm
  • Mesoglea present between ectoderm and endoderm
• Triploblastic animals: Have three embryonic layers:
  • External ectoderm
  • Middle layer of mesoderm
  • Internal endoderm
  • Mesoglea is absent. Instead, the mesoderm is present between the endoderm and ectoderm.

Lateral Line System

• The lateral line system (LLS) is a sensory organ found in aquatic vertebrates.
• It detects movement, vibration, and pressure changes in the surrounding water.
• Hair cells, modified epithelial cells, respond to displacement caused by motion and transduce these signals into electrical impulses through excitatory synapses.

Basis of Classification

• Several key characteristics are used to classify animals:
  • Body symmetry
  • Nature of coelom
  • Patterns of digestive, circulatory, and reproductive systems
  • Arrangement of cells in germ layers

This quiz explores the fundamentals of animal taxonomy, including its significance, methods of classification, and the distinction between taxonomy and systematics. You will learn about the hierarchical structure of classification as exemplified by various species.