32 Overview of Animal Diversity HANDOUT

Introduction to Animal Diversity

  • Overview of Chapter 32 covering animal diversity and characteristics

Key Concepts

  • Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers.

  • The history of animals spans over half a billion years.

  • Classification of animals can be done based on body plans.

  • Emerging molecular and morphological data continue to shape views on animal phylogeny.

Extant Animal Species

  • Over 1.3 million living animal species have been identified.

Definition of Animals

  • Animals are defined as efficient consumers of other organisms, with adaptations to detect, capture, eat, and digest food.

Characteristics of Animals

  • Multicellular eukaryotes.

  • Heterotrophic, relying on other organisms for nourishment.

  • Tissues develop from embryonic layers.

  • Structural support is provided by proteins rather than cell walls, unlike plants.

  • Unique characteristics include the presence of nervous tissue and muscle tissue.

Levels of Organization

  • Movement and nerve impulse conduction are pivotal adaptations distinguishing animals from other life forms.

Animal Reproduction

  • Animals typically reproduce sexually, involving haploid sperm and diploid zygotes.

Zygote Development

  • Stages of Development:

    • Cleavage leads to eight-cell stage.

    • Formation of a blastula (hollow ball of cells).

    • Gastrulation involves the formation of the endoderm, ectoderm, and blastopore.

Developmental Variations

  • Some species develop directly into adults, while others have a larval stage:

    • A larva is a sexually immature form distinct from adults; it often has different food requirements and habitat.

    • Metamorphosis transforms larvae into juvenile forms resembling adults but not yet sexually mature.

Genes Controlling Development

  • Adult morphology varies widely, but developmental genes are similar across taxa:

    • Homeobox genes regulate the expression of various genes.

    • Hox genes influence morphology during embryonic development.

History of Animals

  • The history of animals stretches more than half a billion years, with

    • Origin of multicellularity requiring cell adhesion and signaling.

    • Identifying protist groups closely related to animals through morphological and molecular evidence.

Neoproterozoic Era (1 Billion-542 Million Years Ago)

  • Earliest macroscopic fossils, Ediacaran biota (~560 MYA):

    • Early soft-bodied eukaryotes like molluscs, relatives of sponges, and cnidarians.

    • Evidence of early predation and varied body symmetry and structures.

Paleozoic Era (542-251 Million Years Ago)

  • Cambrian Explosion (535-525 MYA):

    • Rapid emergence of diverse animal forms including arthropods, chordates, and echinoderms.

    • Characteristic development of hard skeletons and bilateral symmetry.

Post-Cambrian Evolution

  • Continuous increase in animal diversity, with vertebrates becoming top marine predators and some arthropods adapting to terrestrial habitats.

  • Vertebrates' colonization of land began ~365 MYA, evolving into diverse terrestrial groups.

Mesozoic Era (251-65.5 MYA)

  • Evolution of animal phyla led to new habitats being explored:

    • Formation of coral reefs, appearance of large dinosaurs and the first mammals, and significant insect diversification.

Cenozoic Era (65.5 MYA-present)

  • Mass extinctions affecting terrestrial and marine animals, leading to the rise of large mammalian herbivores and predators that filled ecological vacuums.

Body Plans of Animals

  • A body plan includes morphological and developmental traits:

    • Symmetry, tissue structure, body cavities, and developmental pathways.

Symmetry

  • Asymmetry: No symmetry, not dividable into equal halves.

  • Radial Symmetry: Parts arranged around a central axis.

  • Bilateral Symmetry: Distinct right and left halves, allowing for organized body structures.

Tissues

  • True tissues are isolated by membranous layers; sponges do not have true tissues.

  • Germ Layers:

    • Ectoderm: Forms outer covering and nervous system.

    • Endoderm: Forms digestive tract.

    • Mesoderm: Forms muscles and other organs.

Body Cavities

  • A coelom is a fluid-filled cavity between the digestive tract and body wall:

    • Coelomates: Have a true coelom.

    • Pseudocoelomates: Have a pseudocoelom (partial).

    • Acoelomates: Lack a body cavity.

Developmental Modes

  • Protostome and Deuterostome modes vary in cleavage patterns, coelom formation, and fate of the blastopore.

Phylogeny of Animals

  • Evolving views of animal phylogeny are shaped by both molecular and morphological data, with ancestral protists leading to major animal groups.