1 Animal Phylogeny 2025

Animal Diversity: Phylogenetic Relationships

General Overview

• Introduction to Animal Diversity

• Spring 2025

• Focus on phylogenetic relationships within the animal kingdom.

Characteristics of the Animal Kingdom

• Animals are:

  • Multicellular

  • Heterotrophic

  • Eukaryotes

  • They lack a cell wall (Chapter 32)

Tissues in Animals

• Most animals possess tissues:

  • Definition: A tissue is a group of cells arranged in a specific pattern or layer with a common function.

  • Tissues arise from embryonic layers called germ layers.

  • Example: Kidney tissue.

Unique Tissue Types in Animals

• Animals have two unique tissue types:

  1. Nervous Tissue

     • Composed of neurons and supporting cells.

     • Function: Conduct signals.

  2. Muscle Tissue

     • Function: Movement through contraction.

     • Contraction is a result of the interaction between actin and myosin.

Understanding Animal Diversity

• Quote by Theodosius Dobzhansky: "Nothing in biology makes sense except in the light of evolution."

Phylogeny

• Definition: Classification scheme based on evolutionary relationships.

• It is a hypothesis explaining the available evidence from various sources.

• Refer to Figure 32.11 for visual representation.

Monophyletic Animal Kingdom

• The animal kingdom is monophyletic, indicating it is derived from a single common ancestor.

• This common ancestor is believed to have been a unicellular protist.

Classification within the Animal Kingdom

• Eumetazoa and Metazoa classification categories:

  • Animals are classified into the Metazoa group —all are multicellular.

  • Distinction based on presence of true tissues:

    • Parazoa: Lacks true tissues; e.g. Phylum Porifera.

    • Eumetazoa: Presence of true tissues.

Symmetry in Animals

• Symmetry Definition: Correspondence in size and shape of the body's sides when divided by a median plane.

• **Types of Symmetry:

  1. Radial Symmetry:

     • More than two planes divide the body into similar halves.

     • Body arranged around a central axis.

  2. Bilateral Symmetry:

     • Animal can be divided into mirror-image right and left sides.

     • Often associated with cephalization—concentration of nervous and sensory structures at the anterior end.

Overview of Animal Development

• Fertilization: Results in a diploid zygote.

• Cleavage: The zygote undergoes multiple cell divisions (cleavages).

• Blastula: Hollow ball of cells stage.

• Gastrulation: Formation of a layered embryo (gastrula).

• Invagination may occur during gastrulation.

Germ Layers in a Gastrula

• Key Germ Layers:

  1. Ectoderm: Forms outer covering and nervous system.

  2. Endoderm: Forms gut, liver, lungs.

  3. Mesoderm: The third layer present in many animals, forms between ectoderm and endoderm.

Diploblastic and Triploblastic Development

• Diploblastic animals: Develop from embryos with 2 germ layers.

• Triploblastic animals: Develop from embryos with 3 germ layers.

Body Plans of Bilateria

• Acoelomate Body Plan:

  • No body cavity, e.g. Phylum Platyhelminthes (flatworms).

• Pseudocoelomate Body Plan:

  • Body cavity present, but not enclosed by mesoderm-derived tissue, e.g. Phylum Nematoda (roundworms).

• Coelomate Body Plan:

  • Body cavity present and enclosed by mesoderm-derived tissue, e.g. Phylum Annelida (segmented worms).

Developmental Patterns in Animals

• Protostome Development:

  • Blastopore fate: Mouth; Cleavage: Spiral.

  • Examples include molluscs and annelids.

• Deuterostome Development:

  • Blastopore fate: Anus; Cleavage: Radial.

  • Examples include echinoderms and chordates.

Types of Cleavage

• Radial Cleavage: Typical of deuterostomes.

• Spiral Cleavage: Typical of protostomes.

Major Lineages of Animals

• Deuterostomes: Include echinoderms and chordates.

• Protostomes: Divided into two groups:

  • Lophotrochozoa: Possess lophophores and/or trochophore larvae (includes ectoprocts, molluscs, annelids).

  • Ecdysozoa: Shed their exoskeleton to grow (includes arthropods and nematodes).