Overview
This chapter introduces the concept of animal biodiversity, focusing on animal classification, body plans, key characteristics of animal phyla, and the ecological roles of invertebrates.
Introduction to Animal Biodiversity
- Biodiversity refers to the variety of life on Earth, especially the large number of animal species.
- All animals belong to Kingdom Animalia, which is divided into different phyla based on body plan differences.
- Approximately 1.5 million animal species have been recorded.
Animal Classification and Phyla
- Animals are sorted by similarities and differences into groups called phyla.
- Examples of phyla: Porifera (sponges), Cnidaria (jellyfish), Platyhelminthes (flatworms), Annelida (earthworms), Arthropoda (insects), and Chordata (mammals).
- Each phylum is defined by unique structural characteristics.
Key Features of Animal Body Plans
- Body plans include body symmetry, cephalisation, tissue layers, number of gut openings, and presence of a body cavity.
- Symmetry types: asymmetrical, radial, and bilateral.
- Cephalisation is when sense organs and the brain are concentrated at the head, first seen in Platyhelminthes.
- Sessile animals are those attached to one place for life, e.g., sponges.
Body Symmetry and Cephalisation
- Bilateral symmetry is associated with more advanced, active animals.
- Animals with bilateral symmetry usually have cephalisation and are more mobile.
- Radial symmetry allows movement in multiple directions but with less specialization.
- Asymmetrical animals lack symmetry and are typically less complex.
Key Terms & Definitions
- Phylogenetic tree — a diagram showing evolutionary relationships among organisms.
- Phylum — a taxonomic rank below kingdom and above class.
- Taxonomist — a biologist who classifies organisms.
- Body plan — fundamental structural features that characterize animal groups.
- Cephalisation — development of a head with sensory organs.
- Sessile — immobile and fixed in place.
- Symmetry — balanced distribution of identical parts on either side of a dividing line.
- Gut — the alimentary canal or digestive tract.
Action Items / Next Steps
- Review the key features of animal body plans.
- Study examples of different animal phyla and their defining traits.
- Practice identifying body symmetry and cephalisation in various animal diagrams.
- Complete end-of-topic exercises for reinforcement.