8.27.1 Lesson: Kingdom Animalia

Kingdom Animalia

Objective:

H.1 – Identify the characteristics of Kingdom Animalia and its various phyla.

Vocabulary

General Characteristics

Animalia is the most diverse kingdom in the scientific classification system. To better visualize the diversity of this kingdom, it is important to note that an estimated nine to ten million different species of animals inhabit the earth!  Animals range from microscopic creatures that consist of only a few cells to the largest known animal, the blue whale, that weighs over 300,000 pounds! Below is an image (left) of a rotifer, one of the smallest known animals, that is approximately 0.1-0.5mm long. The image to its right is of a blue whale, which measures up to 98 feet long!

Though the rotifer and the blue whale look nothing alike at first glance, they are classified in the same kingdom based on shared characteristics. All organisms within Kingdom Animalia meet the following requirements:

• Eukaryotic: cells within the organism contain a nucleus and membrane-bound organelles
• Multicellular: organism is made up of more than one cell
• Heterotrophic: organism relies on outside sources for nutrients
• Motile: organism is able to move
• Lack cell wall: cells of the organism do not contain a cell wall
• Sexual Reproduction: genetic information from two individuals combine to produce offspring
• Blastula Stage of Development: adults develop from small masses of unspecialized cells

Embryonic Development

All adult animals develop from a small mass of unspecialized cells. During sexual reproduction, a male’s sperm fuses with a female’s egg to produce a zygote. The zygote then undergoes division, and in animals, becomes a blastula. A blastula is a sphere of cells that fold inward to create an inner cavity filled with fluid.

During this stage of development, cells in the blastula are arranged in an inner and outer layer. The inner cell mass is involved in the formation of the embryo and contains stem cells that will differentiate into different types of cells needed by the organism. The outer layer contributes to the formation of the placenta, which nourishes the embryo during development.

Body Symmetry

One method of classifying animals involves analysis of body symmetry. Types of symmetry include bilateral symmetry, radial symmetry, and asymmetry.

Bilateral Symmetry

The division of an animal into equal right and left halves indicates bilateral symmetry, resulting in a mirror-image. Animals that identify with this type of symmetry have a head and tail, front and back, and right and left sides. Examples of bilateral organisms include humans, vertebrates, octopi, spiders, clams, insects, etc. Below is an image that depicts how a butterfly exhibits bilateral symmetry since it can be divided into equal left and right sides.

Radial Symmetry

Animals that have body parts arranged around a central axis have radial symmetry. These organisms are not recognized by a head and tail, or left and right sides, rather they are identified as having top and bottom surfaces. Any imaginary cut through the middle results in an equal division of the animal. Organisms that have a radial body plan are typically aquatic and include animals such as sea stars and sea urchins. Below is an image of a starfish that displays how it can be divided equally when “cut through” the center at different angles. 

Asymmetry

An organism with asymmetric symmetry is not symmetrical at all. If you made an imaginary cut through the organism, there is not a single angle that can be used to create two identical sides or halves. Animals such as sponges and coral are typically asymmetrical. The image below is of an asymmetrical sponge in the Caribbean Sea.

Vertebral Column

Animals can also be classified by the presence or absence of a vertebral column (spine). Vertebrates are animals with a backbone or spinal column and invertebrates are animals without one. Most animals on earth are invertebrates; in fact, there are approximately two million identified invertebrates compared to roughly 57,000 vertebrates. Invertebrates are typically small in size and include flatworms and various insects while vertebrates are much larger in size and include humans, mammals, fish, birds, amphibians, and reptiles.

Human Distinction

The characteristics of animals as outlined by the current scientific classification system place man in the animal kingdom.

However, Scripture reveals that man, unlike any other creature, was created in the image of God. Genesis 1:27 states, “So God created man in His own image, in the image of God He created him, male and female He created them.”

God established man as superior to any and every animal. As seen with Adam, the first man created, God instructed man to exercise dominion over the earth, cultivate the garden and name animals on earth. These tasks and responsibilities are both a command and a blessing from God to man, allowing us to use and care for these created resources in service to God and to one another.

Furthermore, man was given intellectual ability above that of any other part of creation. Man can reason, organize, comprehend beauty, make decisions, laugh, think abstractly, and be self-conscious. Each one of these abilities is non-instinctive, separating us from typical animal-like behavior.

Most importantly, since man was created in the image of God, we have the capacity for knowing who He is and communicating with Him through prayer, praise and worship. We can understand the difference between good and evil, and right and wrong, because of the moral awareness that God has given us.