Animal Diversity Lecture

Overview of Animal Diversity

• Animals exhibit immense diversity but share some common traits.

General Features of Animals

• Heterotrophs: Animals are heterotrophs, meaning they acquire energy and organic molecules through ingestion of other organisms. There are three main categories:

  • Herbivores: Animals that consume plants.

  • Carnivores: Animals that consume other animals.

  • Omnivores: Animals that consume both plants and animals.

• Multicellularity: All animals are multicellular organisms, differentiating them from unicellular forms that are classified as protists.

• No Cell Walls: Animal cells do not have rigid cell walls, which allows for flexibility. They are often structured with extracellular proteins, such as collagen.

• Active Movement: Animals are known for their capability to move actively and complexly compared to other organisms. Moves can include walking, running, flying, and swimming.

Animal Body Plan

• The evolution of animals is characterized by several key innovations:

  1. Symmetry

  2. Tissues

  3. Body Cavity

  4. Embryonic Development

  5. Segmentation

Symmetry

• Most animals exhibit a form of symmetry:

  • Radial Symmetry: Body can be divided into multiple planes (e.g., jellyfish).

  • Bilateral Symmetry: Body can be divided into two mirror-image halves.

Evolutionary Trends in Embryonic Development

• Two main developmental pathways:

  • Protostomes: The blastopore becomes the mouth (e.g., flatworms, mollusks).

  • Deuterostomes: The blastopore becomes the anus (e.g., echinoderms, chordates).

Germ Layers

• During embryonic development, three germ layers form:

  • Ectoderm: Outermost layer (skin, nervous system).

  • Mesoderm: Intermediate layer (musculoskeletal system).

  • Endoderm: Innermost layer (digestive tract).

Body Cavity Types

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

• Pseudocoelomate: Partial lining of mesoderm (e.g., roundworms).

• Coelomate: Fully lined body cavity with mesoderm (e.g., mollusks, annelids).

Major Animal Groups

• Parazoans: Sponges, which lack true tissues and organs; classified in the phylum Porifera. They are filter feeders, capturing food through their porous bodies.

• Eumetazoans: Animals with true tissue organization, including the groups Cnidarians (jellyfish, corals) and Bilateria (including protostomes and deuterostomes).

Cnidarians

• Ancient group of animals, characterized by:

  • Body Forms: Two forms: Polyp (sessile, mouth facing up) and Medusa (free-floating, umbrella-shaped).

  • Classes: Cnidarians are categorized into five main classes:

  • Anthozoa: Sea anemones and corals (polyps).

  • Cubozoa: Box jellies (highly venomous).

  • Hydrozoa: Hydroids, often colonial.

  • Scyphozoa: True jellyfish (medusa stage predominant).

  • Staurozoa: Star jellies, stalked medusa form.

Platyhelminthes (Flatworms)

• Phylum includes ciliated, soft-bodied animals exhibiting:

  • Bilateral Symmetry

  • Acoelomate Body Plan: With an incomplete digestive system (one opening).

Nematoda (Roundworms)

• Extremely abundant, possess a complete digestive system and an incomplete body cavity.

Mollusca

• Coelomates with a complete digestive tract:

  • Body Structure: Composed of visceral mass, muscular foot, and mantle.

  • Types: Includes gastropods (snails), cephalopods (octopuses), and bivalves (clams).

Annelida

• Segmented worms with:

  • Fluid-filled coelom aiding in movement.

  • Well-developed circulatory and nervous systems.

Arthropoda

• Largest animal group, exceeding 30 million species, characterized by:

  1. Jointed appendages

  2. Exoskeleton made of chitin

  3. Body segmentation.

  4. Complex nervous system

  5. Various respiratory organs (gills, tracheae).

  6. Open circulatory system.

• Classes: Insects (highly diverse), Arachnids (spiders), Crustaceans (crabs).

Summary

• Animals share fundamental features such as heterotrophy, multicellularity, the absence of cell walls, and complex movements. They exhibit various body plans and complexities, leading to vast diversity across different forms, structures, and mechanisms of reproduction and survival.