G1) All animals Share the same Characteristics, these are:
  • Eukaryotic cells
  • Multicellular (specialized cells)
  • No cell walls
  • Motile in some stage of their life
  • Heterotrophic
  • Perform Respiration
  • Reproduce (sexually or asexually)
  • Get rid of waste
Most Animals:
  • Have specialized organs and tissues
  • Are heterotrophic by ingestion
  • Have two unique types of muscles
  • Have similar early development


Knowing the characteristics that all animals share allows to not only expand our knowledge about animals, but it also allows us to clearly identify and differentiate animals from other species, which will further augment our understanding of the world.

G3) Three evolutionary trends in animals as they become more complex in form are:

Higher level of organization: As the first cells of most animals develop, they differentiate into specialized cells. The very basic animals are made up of some specialized cells, with no specialized tissues or organs. As animals have evolved over time, the more complex animals are able to organize their specialized cells into tissues, which is a group of cells that perform a similar function. Some of the most complex animals' tissues combine during growth and development to form organs. These organs can work together to make up organ systems that carry out complex functions.

Increase number of germ layers: The most basic of animals have no germ layers at all. This leads to a lack of organs, muscles, nerves, etc. As the animals increase in complexity, two germ layers are present, the ectoderm and endoderm. The most complex animals have all three germ layers; the ectoderm, endoderm, and mesoderm. With a mesoderm, animals are able to form a coelom - a fluid filled body cavity which provides a space in which internal organs can be suspended, and room for those organs to grow. With a coelom, animals are able to become very complex, and carry out many functions.

Cephalization: The simplest of animals have no definite "head" area, or are to have an absence of cephalization. As animals increase in complexity, they display some cephalization, where the concentration of sense organs and nerve cells at their anterior end are placed. Chances are, if an animal has pronounced cephalization, it will be more successful. Symmetry is closely related to cephalization, as the bilaterally symmetrical animals show some sort of cephalization, while the asymmetrical and radially symmetrical animals show no cephalization.


Understanding evolutionary trends in animals allow us to correctly and efficiently identify which animals evolved from which animals, and also be an evidence to the theory that all animals come from the same common ancestor.

G4) The differences between acoelomates, pseudocoelomates and coelomates are:

The different types of body cavities in the animal kingdom.
The different types of body cavities in the animal kingdom.


- Does not have a coelom
- Made of fluid-filled extracellular spaces/tissue
- Common with flatworms


- As the name "pseudo" suggests, these types of animals have false/fake coelom. This means that the coelom is only partially lined with the mesoderm.
- Common with roundworms.


- These types of animals have a real coelom, which is a fluid-filled body cavity completely lined with the mesoderm that contains internal organs.
- Commons with segmented worms.

Advantages of having a coelom:

- Allows room for complex internal organs to develop
- Allows the animal to have 2 sets of muscle tissue (Body wall muscle + digestive tract muscle)
- Allows blood vessels to exist separately (gives space)


Knowing which animals have coeloms is significant as it can aid us in classifying these animals to specific groups and to understand how these animals can differ from each other from the differing types of coeloms.

An example of segmentation in an earthworm.
An example of segmentation in an earthworm.

Segmentation is the division of the body into numerous repeated parts, or segments; usually exhibited by bilaterally symmetrical animals as they develop. Segmentation has been important in animal evolution because of the way genes control the production and growth of body segments. If an organism has segmentation, simple mutations can cause changes in the number of body segments. Different segments can also become specialized, such as having a head or specialized limbs. Some of the most successful animal groups exhibit some sort of segmentation. Animals can increase in size by adding more identical segments, and different segments can adapt to carry out special functions.


Segmentation is very important to understand as in animal evolution, it taught us how the genes can control the production and growth of body segments. Genes can be further tied and related to DNA, reproduction, etc.

G6) There are a couple of reasons why sponges are different from all other animals on this planet. These reasons are they don’t have a mouth or gut and they only contain specialized cells. Below are some key parts of a sponge and what their functions are.
Epidermal cells- Cells that form a protective outer layer of the sponge
Collar cells- Circulates water through sponge
Amebocytes- Travels around the sponge and distributes food and oxygen
Spicules- Provides protection


Sponges and its key parts are significant to understand and learn because sponges are important to the marine economy and are the simplest forms of animals. Its characteristics allows us to distinguish it as animals, even though they are nothing like the animals we are used to.

The life cycle of a parasitic worm.
The life cycle of a parasitic worm.

Worms with a parasitic lifestyle are all around us. A parasite is an organism that lives in or on another organism, known as the host, and benefits by deriving nutrients at the host's expense. These parasite must be able to adapt to their lifestyle, and do so in many ways. A parasite does not want to grow too large, or else it will kill the host, which leads to a lack of nutrients. Their sensory receptors are reduced or absent due to the fact that little sensory information is required. Parasitic worms generally have a reduced digestive system, if they feed off of tissues. Parasites are able to have highly developed reproductive systems as there are hazards involved in transferring eggs from one host to another; natural selection has favoured the production of a large amount of eggs, due to the absent or a reduce digestive system. Parasitic worms' life cycles involved two or more hosts, known as the primary host and the intermediate host. In the primary host, sexual reproduction of the worms takes place, where as in the intermediate host(s), asexual reproduction takes place. The intermediate host(s) may also act as vehicles for carrying larvae to the primary host. Intestinal parasites need protection against digestive enzymes and immune response of the host, and they get this from the tegument and the cuticle. The tegument is a modified epidermis which is folded to increase surface area and make absorption of nutrients more efficient. The cuticle is a tough, non-living covering secreted by the epidermal cells of a worm. Intestinal parasitic worms also need hooks and suckers to attach to the intestinal wall of the host, and get nutrients from the host. Some examples of parasitic worms and how they enter a human body include:
  • Chinese Liver Fluke (Contracted from raw fish)
  • Tapeworm (Obtained by eating raw meat; scolex contains hooks and suckers to attach to the intestinal wall, no digestive system, no nervous system, and a highly developed reproductive system)
  • Blood Flukes (Enter through the skin and get into the blood vessels)
  • Ascarids (Consuming food or water containing eggs; burrow through the intestinal wall)
  • Hookworms (Get into the feet of a human from contaminated soil; use sharp teeth and hooks to burrow into skin)
  • Trichinella (Eating meat with the larval worms; under-cooked meat, pork)
  • Filarial Worms (Black fly bites infected human, ingests the larvae, then bites another human)
  • Leeches (Attaches to the outer surface of an animal; the leech sucks the host's blood, secreting a substance, known as an anticoagulant, that keeps the blood from clotting)


Parasites are especially important to learn about so that when we are infected with parasites, we are able to defend and protect against it. Also, understanding how parasites work can help us understand what characteristics they have that makes them a parasite.

G8) A primary host for a parasitic worm is where the parasitic worm is found and where sexual reproduction occurs.
An intermediate host for a parasitic worm is where a parasite is present during a short transition period in their life. Intermediate hosts occasionally act as a way of transportation for the parasitic worm to get to the primary host.

The following is the Hydatid Tapeworms life cycle. First off an animal passes the hydatid tapeworms eggs onto the ground with its feces. Another animal then consumes the eggs when it eats the grass that has been contaminated with dog feces. The eggs of the Hydatid Tapeworm are then hatched in the animals gut. Larva then hatches out of the eggs and makes their way to the brain, liver and lungs and stay there as a Hydatid cyst. Next the sheep dies and then is consumed by an animal or human and they may also eat the hydatid cysts. At this point the cysts make their way to the intestine and mature into a tapeworm. The tapeworm then begins to produce eggs and they are taken out with the animal’s feces. At this point the eggs may be consumed again by another animal starting the process all over again.


Again, parasites (more specifically, the primary and intermediate hosts) are significant as it allows us to counter and prepare us when parasites do attack our body or help us prevent it from even happening.

G9) The embryonic development in animals goes much like:

- The sperm cell (n) and egg cell (n) will meet and undergo fertilization, which will form a zygote (2n)
- The zygote undergoes cell division/cleavage and will form a hollow ball of cells, as known as blastula.
- The cells will divide + each divided cells will become smaller and smaller, which allows the gastrula to remain the similar (if not same) size, compared to a zygote (cells move inward
during this process).
- The cells will develop continuously to the point where they begin to specialize.
- The three germ layers (endoderm, ectoderm, mesoderm) are layers of the developing animal. The germ layers are layers of cells in the embryo that helps specific tissues in the adult
to form
- After the embryonic development have been fulfilled, the embryo may become a "mini-me" of the adult, through the process of direct development, or become a larva (an immature
stage that looks + acts nothing like the adult, until it undergoes metamorphosis [a process where it changes shape dramatically as they grow] ) .
- The whole larva process is done through indirect development

Adult --> meiosis --> fertilization --> zygote --> cleavage --> blastula --> gastrula --> embryo --> larva / miniature version of adult.

embryonic development2.jpg
A simple diagram showing the steps of embryonic development


The embryonic stage is a crucial subject to learn about as embryonic stages of most animals are extremely similar. Understanding how the process works and why we all become differentiated is important in helping us understand how animals evolve, grow, and develop.

G10) Digestive system- Earthworms have a great digestive system that allows them to eat and digest soil and sand. First off their pharynx takes in the soil and carries it to the esophagus which then carries the food to the crop. The crop is a large storage organ which stores food and soil before moving it to the gizzard where the food and soil is grinded down. After the soil and food are grinded down they are brought to the intestines where it is digested and absorbed into the blood. The last step of the digestive system is when the sand, soil and digested food exits out of the anus.
external image earthw4.jpg
Circulatory system- Unlike flatworms and roundworms, earthworms have a fluid called blood that takes oxygen around to all the cells of the worms body. The blood also carries carbon dioxide from body cells to the epidermis where it is diffused out.The protein that carries the oxygen that is present in the blood is called hemoglobin. The circulatory system involves blood and blood vessels.
external image 9891741_orig.jpg?129
Excretory system-nitrogen waste are carried out of the worms body and blood by diffusion into structures called nephridia. Most segments have two nephridia, Nitrogen wastes are excreted through and opening in the body wall.


The digestive, excretory, and circulatory systems are obviously important to learn as not only do we have them, but knowing how they function in different animals can help us understand and be evidence towards biology and how animals are related to each other.

G11) The ecological roles are:


- Provides: shelter for other marine animals (sponges, cnidarians, worms, etc.) to live on/in/under it.
- Have symbiotic relationships with non-animal organisms, such as: symbiotic bacteria, blue-green bacteria, plant-like protists (which provides oxygen to sponges and remove
sponges' wastes)
- Plays an important role as diets of certain snails, starfish, and fishes.


- Have symbiotic relationships with sea anemones. They protect the sea anemones from predators and clean them, in turn for protection + scraps of food from sea anemones.
- Provide habitats for marine animals by forming corals and reefs --> these corals + reefs are built from many separate coral colonies attached together, where the marine animals can
live (such places like: within the recesses of tunnels, caves, and deep channels)


- Important diets of many fishes, crabs, and lobsters as well as flounders
- Condition soils + aerate them by constantly burrowing through ground (also speeds up the process of returning nitrogen and other important nutrients from dead organisms which
can be used by plants)


The ecological roles of different phyla we studied are important as it not only helps us appreciate them much more, but it also forces us to understand how important they are to specific ecosystems, and that we should not just kill them without thought when we see them.

Terms to Know:

Left - A radially symmetrical animal, Mid & Right - A bilaterally symmetrical animal
Left - A radially symmetrical animal, Mid & Right - A bilaterally symmetrical animal

The anterior end is the front end of a bilaterally symmetrical animal.
The posterior end is the back end of a bilaterally symmetrical animal.
The ventral side is the lower side of a bilaterally symmetrical animal.
The dorsal side is the upper side of a bilaterally symmetrical animal.
The medial is the axis from the centre of an organism to one or other side.
The lateral is the axis from the left to right side of the body.