Animals

If you thought the protist kingdom was diverse you will soon learn that organisms in the Animal kingdom show great variations in particular characteristics. Biologists believe that animals evolved from protists. All animals are heterotrophic and multicellular.

The evolutionary divergence arises from the development of specialized tissue like nervous tissue and muscle tissue. Most animals reproduce sexually. They lack chloroplast and chlorophyll so they cannot manufacture carbohydrates like plants. Animal cells lack a cell wall, but they do have membrane bound organelles and a distinct nucleus.

A labelled diagram of an animal cell appears below.

(Mini) Task Generate a list of 10 different animals. Later you will classify each one based on its characteristics. Remember, animals are diverse, so include a good variation. DO IT NOW!

Classification The two main classifications of animals are vertebrates and invertebrates. Most animals are invertebrates and include jellyfish, worms, octopus and lobsters. The animals in these phyla do not have a backbone. Vertebrate animals have a backbone, called a notochord, during some portion of their life cycle. These animals are more familiar because they are dominant on land and in water. Vertebrates are structurally bigger than invertebrates and include fish, birds, frogs and humans.

Question Below are images of organisms that belong in the Animal kingdom. For each animal, classify it as either an invertebrate or a vertebrate.

Answer Invertebrate – Butterfly, Coral & Preying Mantis. Vertebrate – Bison, Pelican & Salamander.

There are 33 phyla in the animal kingdom. In this activity we will examine one representative invertebrate and one vertebrate animal. enTI enTI Stop at 4:55

Invertebrates Invertebrates make up approximately 95% of all of the identified organisms on the planet. Invertebrates live in a wide range of habitats from dark forests to the deepest trenches of the oceans. They inhabit land, air, and aquatic habitats. There is a lot of variety in the invertebrate group; however, the one characteristic that they all share is the absence of a backbone.

The Earthworm Have you ever wondered why worms only come out to play when it is raining? Earthworms belong to the phylum Annelida along with additional species. An earthworm with two regions highlighted. (1)Clitellum which is involved in reproduction. (2) Segmentation.

Physical Structure Earthworms have segmented bodies. If you look at the image above and on the right side, you will notice divisions along the length of the worm. On average there are approximately 100 segments. Segmentation is beneficial for movement because it allows the worm to be flexible. It is capable of moving a few segments at a time instead of moving its entire body at once.

Earthworms show bilateral symmetry which means that their bodies, if cut lengthwise down the middle, will mirror each other. Bilateral symmetry is an evolutionary advancement from radial symmetry. Worms have a definite head region with nerve cells that indicates brain development. This allows earthworms to assess their environment as they move and adjust and react appropriately to changes. Radial symmetric invertebrates lack a definite head region and therefore their movements are more random.

All earthworms have a body cavity called a coelom. This cavity protects the internal organs of the worm. Recall that all animals have specialized tissues as one of their evolutionary adaptations. In addition to sensory nerves, worms also contain organ systems like digestive, respiratory, circulatory and reproductive. Note, not all invertebrates contain a body cavity, only higher functioning invertebrates have a coelom.

Virtual Worm Tour

Habitat Earthworms live in moist environments. Generally they burrow in soil because it provides them with nourishment and keeps their outer layer moist which is important for their survival. Worms take in oxygen through their skin which is covered in tiny mucus-secreting cells. Dry skin means death to a worm. So when it rains, the wet ground is easier for worms to move on; consequently, it is easier for the worm to find a mate in an open area rather than in its burrow.

Reproduction Earthworms are hermaphrodites which mean they contain both male and female sex organs. This does not mean that they can self-fertilize. Each worm must find a mate of the same species to reproduce.

An earthworm is ready to mate when its clitellum changes colour from pinkish to red- orange, as shown in the figure to the right. Two earthworms line up in a head to tail fashion and exchange spermatozoa (sperm), as shown in the diagram below.

A slime tube then forms around the clitellum, which dries and fills with a fluid called albumin. The earthworm then wiggles out of the tube head first. The tube passes over the female pore which deposits ovum (eggs) into the capsule.

Further Reading logyPages/I/Invertebrates.html logyPages/I/Invertebrates.html