Kingdom Animalia – Part One

Remember…we’re talking about Kingdom Animalia

What characteristics do all members of the animal kingdom share?

Characteristics of Kingdom Animalia

1) Multicellular – what might be the benefit of being multicellular?

2) Eukaryotic – their cells each have membrane-bound organelles and a nucleus

3) Heterotrophic – animals are unable to obtain energy from the sun, so they need to consume other organisms

4) Animal cells lack cell walls (this, among other things, makes us different from plants!)

Animal Cell vs. Plant Cell

• Look at the diagram below. Notice animal cells are surrounded just by a cell membrane while plants have a cell membrane and a rigid cell wall

Cell Wall

Animal Kingdom has 2 Main Groups

Invertebrates• Lack a backbone• 97% of all species on Earth

are in this category

Vertebrates• Have a backbone for at least

part of their history• Only one phylum (Chordata)

Evolutionary Trends of K. Animalia

• If we examine the basic body plan of the members of K. Animalia, we find that they exhibit four major evolutionary trends:

1) Multicellular Development of Tissues

2) No symmetry Bilateral Symmetry3) 2 Germ Layers 3 Germ Layers4) Acoelomate (no gut) Coelomate (gut

surrounded by cells)

Trend #1 Multicellular Tissues

• Remember: multicellular means you are made up of more that 1 cell. Humans, for example, are made of trillions of cells

• The benefit of being a multicellular organism is that your cells can group together to form “tissues” that can them be specialized for different functions (i.e. become organs).

• Simple animals are multicellular; however they lack true tissues (e.g. sponges). In more complex animals, cells start to form tissues and simple organs

Types of Tissues Found in Complex Animals

Trend #2: Body Symmetry• There are three main types of body symmetry: no

symmetry(asymmetrical), radial symmetry, and bilateral symmetry

• Radial means you can divide the organism into more than 2 equal parts while bilateral means you can divide the organism into 2 like parts.

Trend #2: Body Symmetry

Why would it be beneficial to be bilateral?As you can see below, bilateral species have developed different body regions (anterior = head; dorsal = back) allowing these regions to specialize into different functions (head = sensory organs).

Trend #3: Development of Germ Layers

All animal life begins with a single fertilized egg

The single egg divides multiple times to form a small ball of cells called a blastula (yes you were once a blastula!)

The blastula later develops into “germ layers” (ectoderm, endoderm and mesoderm)

Trend #3: Development of Germ Layers

Each of these layers becomes specific tissues in an adult

Ectoderm – skin, nervous system (in more complex animals it also becomes feathers, scales, hair and nails)

Mesoderm – present in more complex animals. Forms organs of circulatory, reproductive, urinary and muscular system.

Endoderm – form lining of the gut

Why are germ layers important?• Germ layers give us a hint as to how the complexity of

organisms has progressed

• Lower invertebrates (sponges, jellyfish, etc.) lack a mesoderm (only have 2 germ layers) and therefore have no circulatory systems

• In more complex animals, a mesoderm layer (3rd germ layer) is present and it develops into important internal transport systems (digestive systems, circulatory systems, etc.)

Trend #4: Body Cavities • Another evolutionary trend is the development of an

internal body cavity called a coelom. A true coelom is lined by cells from the mesoderm germ layer.

• Some less complex animals groups have “pseudocoelom” (pseudo = false). This is a fluid-filled body cavity that is not surrounded by a layer of cells

• The simplest organisms lack coeloms and are therefore called “acoelomate.” In this case, the gut is not lined by cells or surrounded by a fluid-filled cavity.

Trend #4: Body Cavities

The red circle above is the gut. Notice in the pseudocoelomate, the gut is surrounded by a fluid-filled cavity. In the coelomate organism, the gut is surrounded by a layer of mesoderm cells (in blue).

Why is a coelom important?

• Having a coelom is beneficial because it helps to:– Protects internal organs– Streamlines the organism– Allows for the evolution of more complex organs

and organ systems