chapter 26

Overview of Animal Diversity II Lecture 26 (Chapter 32)

  • Date: 19 July 2022
  • Location: Viking Bay Ko, Phi Phi Le, Thailand
  • Featured Species:
    • Ocellaris Anemonefish (Amphiprion ocellaris)
    • Magnificent Sea Anemone (Radianthus magnifica)

Biblical Perspective on Animal Creation

  • Genesis 1:24 (NIV): "And God said, “Let the land produce living creatures according to their kinds: the livestock, the creatures that move along the ground, and the wild animals, each according to its kind.”"
  • Date: 7 September 2018
  • Location: Maasai Mara National Reserve, Kenya
  • Featured Species:
    • Common Wildebeest (Connochaetes taurinus)
    • Plains Zebra (Equus quagga)

Body Plans: Symmetry

Asymmetrical

  • Characteristics:
    • Irregularly shaped
  • Example:
    • Stylissa massa (Sponges known for their lack of regular shape)
  • Date: 17 December 2017
  • Location: Mana Island, Fiji

Radial Symmetry

  • Definition:
    • Symmetrical around a central point; any line through the central point yields mirror image halves.
  • Features:
    • No central nervous system or cephalization (contrast to bilateral symmetry)
    • Many species are sessile (attached) or planktonic (drifting).
  • Example:
    • Pacific Stubby Rose Anemone (Urticina clandestina)
  • Date: 4 July 2024
  • Location: Mendocino Headlands, California

Bilateral Symmetry

  • Definition:
    • Symmetrical around one line with mirror images on each side. Distinction between anterior (front) and posterior (back) ends.
  • Features:
    • Usually have a central nervous system and exhibit cephalization (formation of a head).
    • Most species are motile (capable of locomotion).
  • Example:
    • European Peacock Butterfly (Aglais io)
  • Date: 8 August 2021
  • Location: Nyzhnya Rozhanka, Ukraine

Comparison of Symmetries

  • Radial Symmetry
    • Oral and Aboral surfaces defined; often found in stationary or drifting organisms.
  • Bilateral Symmetry
    • Anterior, Dorsal, Ventral, and Posterior surfaces defined; aligns with active movement and predation.

Body Plans: Germ Layers

Absence in Sponges

  • Sponges (phylum Porifera) do not possess true germ layers.
  • Example:
    • Large Tube Sponge (Haliclona fascigera)
  • Date: 13 July 2023
  • Location: Changuu Island, Zanzibar, Tanzania

Diploblastic Organisms

  • Structure:
    • Composed of two germ layers: Endoderm (inner) and Ectoderm (outer).
    • Note: Some definitions reference a non-living layer (Mesoderm) but may vary.

Triploblastic Organisms

  • Structure:
    • Composed of three germ layers: Endoderm, Ectoderm, and Mesoderm.

Body Plans: Body Cavity

Acoelomate

  • Definition:
    • Animals lacking a body cavity; their body is a solid mass of cells.
    • Example: General flatworms
  • Germ Layer Composition:
    • Ectoderm
    • Mesoderm
    • Endoderm
    • Digestive cavity present within the mass.

Pseudocoelomate

  • Definition:
    • Body cavity lies between the digestive tract and the outer body wall, originating from the blastopore.
  • Germ Layer Composition:
    • Ectoderm
    • Mesoderm
    • Endoderm
  • Characteristics:
    • Pseudocoelom is not completely surrounded by mesoderm.

Coelomate

  • Definition:
    • True body cavity located between the digestive tract and the outer body wall, lined with mesoderm.
  • Functions:
    • Mesodermal structures serve to suspend and cushion internal organs.
  • Germ Layer Composition:
    • Ectoderm
    • Mesentery (Tissue supporting organs)
    • Endoderm
    • Mesoderm (forming the coelom)

Hemocoel

Definition

  • An open circulatory system found in some phyla where blood-like fluid (hemolymph) transports nutrients, gases, and wastes throughout the organism.

Body Plans: Embryonic Development

Protostome Development

  • Characteristics:
    • Determinate cleavage is evident; the fate of cells is fixed at the 4-cell stage meaning they cannot form a complete organism if separated.
    • Spiral cleavage occurs where cells align obliquely.
    • Mouth formation arises from the blastopore; the anus is formed later from a separate opening.
    • Coelom develops by schizocoely where a solid mass of mesoderm splits.
  • Visuals of Development Stages:
    • Anus and mouth formation details illustrated with stages of gastrulation and coelom formation.

Deuterostome Development

  • Characteristics:
    • Indeterminate cleavage allows for the possibility of separating cells at the 4-cell stage to develop into separate organisms (e.g., twins).
    • Radial cleavage occurs where cells layer directly on top of one another.
    • Mouth is formed from another opening, with the anus originating from the blastopore.
    • Coelom is formed via enterocoely from pouches made in the wall of the primitive gut.
  • Development Stages:
    • Similar diagrammatic representation as in protostomes, highlighting stages of development, cleavage types, and formation processes.

Body Plans of Major Animal Phyla

Comparative Table

  • Highlights the body symmetry, germ layers, body cavity types, and embryonic development stages for several phyla including:
    • Porifera: Asymmetrical, Two layers but no germ layers, Acoelom, Neither.
    • Cnidaria: Radial, Diploblastic, Acoelom, Neither.
    • Ctenophora: Biradial or bilateral, Diploblastic or triploblastic?, Acoelom, Neither.
    • Platyhelminthes: Bilateral, Triploblastic, Acoelom, Protostome.
    • Annelida: Bilateral, Triploblastic, Coelom, Protostome.
    • Mollusca: Bilateral, Triploblastic, Coelom, Protostome.
    • Nematoda: Bilateral, Triploblastic, Pseudocoelom, Protostome.
    • Arthropoda: Bilateral, Triploblastic, Coelom, Protostome.
    • Echinodermata: Radial or bilateral, Triploblastic, Coelom, Deuterostome.
    • Chordata: Bilateral, Triploblastic, Coelom, Deuterostome.

Kingdom Classification

Animal Kingdom

  • Animals belong to the kingdom Animalia.

Phylogeny and Historical Development

Evolutionary Timeline

  • Key clades and timelines represent the evolutionary history of animals with significant markers such as:
    • 770 million years ago: Origin of Metazoa.
    • 680 million years ago: Emergence of Eumetazoa.
    • 670 million years ago: Formation of Bilateria.
    • Major clades include Ecdysozoa, Lophotrochozoa, and Deuterostomia with each defined by unique characteristics such as ecdysis in Ecdysozoa and lophophore in Lophotrochozoa.

Clade Overview

  • Metazoa: All animals, sponges (phylum Porifera) are basal animals.
  • Eumetazoa: Animals with true tissues, includes basal phyla Ctenophora and Cnidaria.
  • Bilateria: Animals with bilateral symmetry, inclusive of three main clades.
  • Deuterostomia: Clade includes vertebrates and defined by deuterostome development.
  • Lophotrochozoa: Characterized by a lophophore feeding structure or trochophore larva.

Study Reference

  • Study recommendation for preparations over lectures 25-26 (Chapter 32).