1. The Three Major Groups of Worms Comparisons and contracts between the three animals.

2. In this assignment I will be breaking down the major characteristics of Flatworms, Roundworms and Segmented worms in a simple allowing my audience to recognize the comparisons and contrasts between the 3 groups.

3. General Characteristics and Parts
Flatworms have a sac body plan, which means that they have no body cavity. They are acoelomate.
Flatworms contain cephalization, which is a concentration of of nervous tissue at the anterior part of their body
These animals are bilaterally symmetrical, which means that their body cavity can be cut in half lengthwise, and the two halves will be identical.
They contain three germ layers, which consist of an endoderm, ectoderm, and a mesoderm. The ectoderm forms outer epidermis, the mesoderm forms muscle tissue and reproductive and excretory organs, and the endoderm forms inner gut.
Due to their mesoderm they have a organ level of organization
Roundworms contain a tube within-a-tube body plan, which means that they are pseudocoelomate.
These animals are more evolved than porfiera, cnidaira, and planeria, as they have two openings, a mouth and an anus, instead of a single opening that acts as both. Having a tube within-a-tube body plan allows the animal to contain specialized digestive organs, instead of retaining nutrients by diffusion which is a very inefficient characteristic.
Roundworms are bilaterally symmetrical, contain 3 germs layers that are very similar to the flatworms, and also contain more advanced cephalization.
Segmented worms, more commonly known as earth worms, are very similar to round worms in many ways.
Segmented worms contain a true coelomate body plan, which is a tube within-a-tube body plan, with very specialized organs.
These animals also have 3 germ layers, and contain cephalization with sensory organs.
They are one of the most primitive animals to contain segmentation, which allows for much more specialized body parts. They also have septa which are the partitions between segments and allow structural support by creating a hydroelastic skeleton. The septa also allow for specialized parts of the digestive system.

4. The nervous system
Flatworms nervous systems are referred to as a “nerve ladder” type of nervous system, since it is made up of two lateral nerve cords connected by transverse nerves, along with cephalization. This nervous system gives them the ability to be much more responsive to the environment around them compared to organisms like cnidaria and porifera, as it allows for them to control their muscles precisely for movement. Flatworms are able to sense predators with the help from their two eyespots, which are part of their cephalization. Eyespots are light sensitive structures on their head that can sense which direction the light is coming from. Flatworms are know for travelling away from the light, as this is where predators often are found.
They are the first animals to start showing signs of a brain, making them a very important step in the evolutionary ladder of animals.
Roundworm’s nervous system does not contain a brain, however it is relatively well developed for such a primitive animal. They have simple sense organs, divided into two parts. A circumpharyngeal nerve ring and longitudinal nerves that extend down the through the worms body to parts of the gut and reproductive organs. The longitudinal nerves show signs of the beginning of the development of the spinal cord. The circumpharyngeal nerve ring is necessary for the roundworm to move, these nerves send nerve impulses to the worm’s muscles to contract and stretch for movement. They contain several ganglia in there head region. Ganglia are groups of nerve cells that forward sensory nerve information to the worms longitudinal nerves and circumpharyngeal nerve ring. Ganglia are the beginning of a true brain.
The nervous system of a segmented worm is very similar to a round worm. It contains a chain of ganglia which is near the ventral, head of the worm, which is connected by a ventral nerve cord. However, segmented worms actually contain a very primitive brain-like structure! They possess a cerebral ganglia, which allows them to respond to light, touch, chemicals, moisture, temperature, and vibrations.

5. Movement
Due to flatworms advanced nervous system, they have the ability to control their movement by using their nerve ladder. The nerve ladder sends messages from the anterior end to the posterior end, to create muscle contractions across the worms body. These movements allow the worm to be a mobile animal. This is another key for the evolutionary path of animals.
Roundworms contains a layer of longitudinal muscles under their skin. Their muscles flex very quickly producing a whip- like wiggle. This is the way that these animals are able to move around. Scientifically this is called undulatory propulsion, which means “limbless locomotion”.
Segmented worms move by contractions of their segmented muscles. They contain longitudinal and circular muscles which work together to coordinate the worms movement. The circular muscles tighten, making the worm long and skinny, next the longitudinal muscles squeeze and pull the front end forward and finally the rear end is pulled toward the front end. This is the sequence of actions that allows worms to move around efficiently.

6. Circulatory System
Flatworms do not contain a true circulatory system as they do not possess a heart. Instead they circulate nutrients and oxygen through part of the gastrovascular cavity similar to cnidaria. Nutrients and oxygen diffuse across different tissues and membranes of the body, allowing nourishment to get to every cell.The reason flatworms are so thinly shaped is it to allow for the process of diffusion to occur easier; if tissues are thin then it is easier for nutrients to move to different areas of the body more quickly.
Round worms do not contain a circulatory system. They do not have blood vessels to transport nutrients and oxygen, instead they retain nutrients and excrete wastes through their body walls by diffusion. The pseuodocoloem is is the area of the worm where the distribution of nutrients to the rest of the body occurs.
Segmented worms are one of the most primitive animals with a true circulatory system. It consists of a dorsal and a ventral blood vessel that extend from the head to the end of the worm. They contain five pairs of branches, called pesudohearts, that connect the two vessels together behind the head region. The five branches resemble a heart, as they are able to pump blood around the entire body with pulsating actions. Blood is pumped from the pseudohearts towards the back of the worm through the ventral blood vessel, and then the blood returns through the dorsal blood vessel. Segmented worms have a very effective circulatory system as they are able to transport oxygen and nutrients throughout the entire body of the worm.

7. Digestive system
The digestive system of planaria, which is one of the more common flatworms, is very similar cnidarians. Since flatworms are acoelomate, they contain only one opening that operates as the mouth and anus. Food will enter through the pharynx of the worm, which is a long and skinny limb-like structure that extends from the underside of the worm and is connected directly into the gastrovascular cavity. Normally you think that the mouth of an animals is part of it’s head or cephalization, but for flatworms their structure that works as their mouth is surprisingly directly attached to the visceral side half way down their body. The pharynx sucks up food, and then sends it to the gastrovascular cavity to get digested by enzymes. The nutrients are absorbed by the animal through it’s gastrovascular lining by the process of diffusion, and is sent to the cells around the body. Whereas, wastes are sent right back out the same opening as it entered the worm.
Since round worms are pseucolomate they contain a complete digestive tract from mouth to anus. They possess specialized digestive organs, which sets them apart from flatworms. This is a more advanced characteristic of animals because food and wastes do not mix. The digestive system starts at the mouth of the worm, their mouth contains three lips, and depending on the species can possess teeth. The lips push the food into the pharynx where it is efficiently pushed into the intestines. Digestion is rapid and nutrients are absorbed by diffusion into the cells of the body. Undigested food remains become feces and will continue on through the tract to be excreted out of the anus. This is the final step of the digestive tract.
The great amount of segmentation that earthworms possess allow development of specialized parts of the digestive system, which is very similar to advanced animals. Their food consists of soil, and it enters the mouth as they burrow through the ground. The food is pushed into the pharynx and then down the esophagus, and into the crop. The crop is where food is stored until it is ready to enter the gizzard where is it broken down mechanically. Next, the food enters the intestine where the food is chemically broken down, and absorbed into the blood stream. Finally, all of the undigested foods are sent through the anus to be excreted.

8. Excretory System
Flatworms create two types of wastes. When food enters the body of a worm, parts of it will be used to nourish the worms but there will also be parts that need to be excreted from the worms body as the worm has no use for them. Some wastes that the worms can tell should not enter it’s body will be expelled straight out of the pharynx immediately. This is a very efficient way for the worm to save energy. By removing substances out of it’s body right away instead of having it pushed around the body for it to be excreted in the end anyways saves a lot of energy for an animal with not proper digestive system. There are also wastes that have entered the body as food for the worm, but have had all out their nutrients absorbed so there is no more use for the substances and they are excreted from the body through the gastrovascular cavity. Planeria contain specialized cells called “flame cells” which help in the process of removing these wastes from their body. A flame cell is a sac-like cell with cilia that beat, they have the ability to move water continuously through the excretory canals and out the excretory pores.
Round worm’s waste exit the body through the anus, which is a hole at the end of the digestive tract. After all of the nutrients have been absorbed by the worms intestines then the rest is waste. The food is pushed through the intestines and to the anus where it is excreted from the body.
Earthworms also produce two types of wastes which are excepted in separate ways. Digested food that are of not use to the worms body are excreted out of the anus. Cellular wastes and excess water are excreted through excretory pores across the surface of the worm. These pores are called naphridia, and they are found in pairs in each segment of the worm. They filter the wastes out of the blood and excrete them without them having to be removed by the anus.

9. Respiration
Flatworms do not contain a respiratory system, as they do not contain lungs or blood vessels of any type. Instead, gas exchange occurs by the process of diffusion. The skin of flatworms is covered with a great amount of pores which allow easy access for oxygen and other gases to move in and out of it’s body. Once the oxygen has entered the worm, it is sent directly into the cells of the animal.
Segmented worms also have no respiratory organs, therefore oxygen and carbon dioxide is diffused through the skin of the worm as well. Once the oxygen has entered the body of the worm it enters small blood vessels and is sent throughout the worm. However, this action can only happen when the worm is moist, therefore worms cannot survive if they are in a very dry and warm environment.
Just like flatworms, roundworms have no true respiratory system. They rely of the process of diffusion to breathe through their body walls. Their pesudocoelom, which is fluid in between their two tubes, distributes dissolved oxygen to the cells all over their body.

10. Feeding Methods
Planeria feed on small animals and the remains of larger dead animals. Some species have the ability to solely live off of the nutrients from a host. Flatworms contain a very primitive digestive system, they contain three germ layers as well as an incomplete gut called the gastrovascular cavity, this is there the food sits once it has entered the worms body through the pharynx. However, having a primitive digestive system is not an issue for these animals as a majority of them are parasitic animals, therefore they get their nutrients directly from other living animals which does not require a great amount of digestion. Useful food particles diffuse across the gastrovascular membrane and across the tissues of the worm to nourish all of the cells. There are no other structures that aid in digestion.
A large amount of round worms are parasitic animals, similar to flatworms, meaning that they retain their nourishment from other living creatures. Many live in the intestines, skin and other tissues of much larger animals, as well as humans. They do not need an advanced digestive system as the nutrients have been previously broken down by the host.
Segmented worms are famous for their important role in maintaining healthy soil all cross the worm. Earthworms push themselves through the dirt in order for it to enter in their mouth. Dirt is filled with organic materials like leaves and compost items, which gives the worms the nutrients they need to survive. An earthworm’s digestive system will break down all of the organic materials, and when it is excreted out of the worm’s anus as feces, then it becomes valuable fertilizer for all of the plants around.
Some species of flatworms are able to absorb food by diffusion through their skin.

11. Reproduction
Some roundworms are hermaphroditic, but most are dioecous meaning that they have separate sexes. Both male and female reproductive organs are found in the pseudocoelom, and takes up a large amount of space compared to the other systems. Female worms have long coiled ovaries that produce thousands of eggs per day, which can be stored in the uterus. Connected to the uterus is the vagina, which leads to an external opening leading out of the worm. The male reproductive organs consist of one testi that is coiled, which produced sperm, and a sperm duct which is a tube that the sperm passes through to get to the opening at the posterior end of the worm in males this is called the penis. During fertilization, sperm is released into the vagina. This process is called internal fertilization and it is a advanced characteristic of roundworms.
Earthworms are hermaphrodites meaning that they contain both male and female reproductive organs, therefore the reproductive process for each worm is the same. The male sex organs are found in the head, and the female sex organs are found in the clitellum. The clitellum is a large band that wraps around the worms body. Earthworms reproduce by cross-fertilization, meaning that they are unable to fertilize their own eggs. Two worms will press up against each other and press their ventral surfaces together with their heads faces opposite directions. A large amount of mucus forms around the two worms, and then they both ejaculate their sperm. The sperm enters the opposing worm, and is stored in a pouch-like seminal vesicle in the worms body. Next a caccoon forms around each of the worms and when they move apart it picks up the worms eggs and stored sperm, this is where fertilization takes place. The caccoon closes up to form a protective case for 2-3 weeks unto they young worms are mature enough to hatch.
Flatworms are hermaphrodites, which means that they contain both male reproductive organs including a penis and testis, as well as female reproductive organs like ovaries. They undergo cross-fertilization between organisms, this means that two individuals fertilize each other through their reproductive process. Flatworms will align themselves side by side one another, facing opposite directions, allowing them to simultaneously fertilize one another.
Another reproductive characteristic of planeria is that they have incredibly efficient regeneration capabilities. If a flatworm is cut lengthwise, down the middle, it will grow into two separate animals.

12. Habitat
There are three different classes of flatworms, the class Turbellaria live in the ocean and some species can be found living in fresh water. And then the other two classes, Trematoda and Cestodae are both parasitic worms that live within either an secondary host, like a snail or primary host, like a human.
Roundworms can live in almost every habitat around the world, including soil, salt flats, aquatic sediments, polar regions and the tropics, however they cannot survive in very dry places as there means of respiration are dependent on water and moisture.
Segmented worms also inhabit areas all over the world. They are terrestrial animals and they usually live in areas with mild temperatures but since their two main surviving needs are soil and moisture they are found all over the world.

13. Image Citation. Work Cited.
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Muscle Movements of Earthworms. Digital Image. June 9, <
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Nematoda Digestive System. Digital Image <
Parasitic Worms Burrow into Walls of Women’s Intestine. Digital Image. Aug. 19, < raw-fish-stomach.html>.
Platyhelminthes Digestive System. Digital Image. <
Respiration In Earthworms. Digital Image. <
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