5.+Platyhelminthes

=__Platyhelminthes– **Flatworms: Taenia Solium**__=

[[image:https://upload.wikimedia.org/wikipedia/commons/2/27/Hymenolepis_microstoma.jpg width="392" height="312" link="@https://upload.wikimedia.org/wikipedia/commons/2/27/Hymenolepis_microstoma.jpg"]]
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__General Facts About Flatworms (Classification and Diagnostic Characteristics__:

 * There are more than 25,000 species of flatworms.
 * Of these 25,000, most are **//tapeworms//** and **flukes**.
 * They typically have a small, basic brain, two eyes, cilia (to move around), and a digestive tract
 * //Taenia solium// has head. Four suckers are attached onto the head.
 * They can grow between 2 m and 8 m.
 * The large body is made with lots of proglottids that contain fully mature reproductive system.
 * **Note that this does not apply to all; some do not have central nervous systems and some do not have eyes. This is merely a broad scope of most flatworms.

__Relationship to Humans__:
- They are sexually reproducing animals and some have brains and eyes. Both have digestive tracks and process nutrients. - They are parasites for humans and can enter the human body through the consumption of raw or infected pork. - They cause cysticercosis, a disease that can cause seizures. - They live in the small intestine of humans and in the case of the pork work, small farm animals including pigs.
 * Cysticercosis is an infection that arises from Taenia Solium. This develops after the ingestion of ova excerated in human http://www.merckmanuals.com/professional/infectious-diseases/cestodes-tapeworms/taenia-solium-pork-tapeworm-infection-and-cysticercosis

**__Predator Avoidance__:**
- Developed anti-predator behavior that results from chemical cue signals that are released - Behavior is triggered by self-releasing signals from an injured planaria, which triggers release of chemicals into environment - Other planaria react to the signals, creating a warning system for the environment

** __Nutrient Acquisition__: **

 * Many flatworms are parasitic. Flatworm larvae can cause severe damage to the host.
 * Carniveores
 * Feed on smaller or dead animal
 * feed on liver, lung or brain of other animals and can cause disease in humans and other animals
 * Flatworms eat anything they can find, dead or alive.

**__Habitat And Niche:__**
//-Taenia solium,// the pork tapeworm, lives in several habitats during the various stages of its life cycle. In its pre-adult and adult stages, the pork tapeworm lives in humans in the small intestine, while its eggs are often found in the feces of the host (both internally in the host and externally when the feces are released to the external environment). During the oncosphere phase of the tapeworm's life cycle the tapeworm lives in the gut tissue of the host pig. When the tapeworm reaches the cysticercus stage of life it lives in the muscle tissue of the pig and the brain of the pig and in this stage can also be found human muscle tissue and the brain. - Has several different habitats depending on the stage in its life cycle. (2) - Preadult and adult tapeworm are located usually in the small intestine of a human host (2) - Some eggs are found in the host feces, and in the external environment where the feces are released (2)

__Nutrient Acquisition__:
- There are internal and external parasites that live either inside or outside of their house -To obtain energy, the flatworms consume digested material or nutritious substances from their host (i.e. blood).

__Reproduction and Life Cycle__:
- Has 6 stages of its lifecycle: preadult tapeworm, adult tapeworm, egg, oncosphere, postoncospheral form, and cysticercus. (2) - The preadult and adult tapeworm occur in the definitive host, the human. (2) - These 2 stages can only happen when the definitive host consumes pork that has been infected by the cysticercus stage because the adult must mature in the definitive host's intestine. (2) - The adult tapeworm is the reproductive stage and single sexually mature proglottid contains an average of 40,000 eggs. (2) - Eggs are shed in the feces of the host and then consumed by a pig, the intermediate host. (2) - The pig ingests the human feces in low sanitation conditions and then the egg sheds its outer shell and becomes the oncosphere larva. (2) - Each segment in a tapeworm has its own set of male and female reproductive systems. As a result, gametes are able to undergo self-fertilization. (2) - However, there have been reports of cross-fertilization between different individuals. ([]) (2)

__**Growth and Development**__**:**
-Fertilized eggs are laid, oftentimes in batches, many at a time -Often, the eggs are attached to a surface via adhesive secretion -Once the eggs finish embryonic development, worms develop

**__Integument__:**
- Outermost thick, waxy layer of skin serves to protect the internal organs and also absorb nutrients from the host's body - The surface of the skin has villi-like appendages that increase surface area to help absorb more nutrients - Under the outer cuticle is circular and long muscles, which make up the layer called mesenchyma - The epidermal cells of the mesenchyma are long-necked

**__General Anatomy of the Flatworm (in order)__:**
Flatworms lack an anus and have very few bodily cavities. They have one opening to take in nutrients and expel waste.
 * Anterior
 * Pharyngeal Opening
 * Gut
 * Testis
 * Yolk Gland
 * Seminal Receptacle
 * Over
 * Vagina
 * Posterior

**__Movement__:**
//T. solium// is a parasite, so for the most part, it stays inside of a host until excreted along with feces or upon surgical removal. Eggs first leave the body though feces. Then, the eggs pass onto local vegetation, allowing days or weeks to pass by before being ingested by an unknowing pig. The eggs move with the digestive system and then the circulatory system until burrowing in muscle and developing into cysticerci, where they can persist for many years. Humans or other pig predators take up the cysticerci by consuming raw or undercooked pork, transferring the eggs once again. Finally, the cysticerci travel to the intestine where they develop and persist as adults, growing until they can reproduce and send their offspring off down the digestive tract. https://web.stanford.edu/group/parasites/ParaSites2006/Taenia_solium/Life%20Cycle.html

**__Sensing the Environment__:**
- Sense organs are absent in the tapeworm, but free nerve endings exist throughout the body Flatworms have "eyes," where they can detect light. These eyes have a single layer of photosensitive cells, which allows the flatworm to detect light.

__**Gas Exchange**__**:**
-The tapeworm lacks a respiratory system or any specialized organ that performs gas exchange.

__**Waste Removal**__**:**
Waste excretion happens through passive diffusion of soluble wastes. They have specialized cells called protonephridia cells which make up their excretory organs and utilize kidneys and has two or more longitudinal branching tubules along the length of the body. Holes open onto the outside of the worms and end in flame cells. Since no circulatory system, the flame cells pick up the wastes.

__**Environmental Physiology (Temperature, water, and salt regulation)**__**:**
Scientists have determined that pickling meat containing //T. solium// will kill the worms, either because the pH decreased to 5.3 or because the worms died from such a high concentration of salt. The same group of scientists also roasted meat containing //T.// //solium// and discovered that the worms died once the temperature increased to over 65°C.

**__Internal Circulation__:**
Tapeworms have no circulatory system.

**__Review Questions__:**
1) What type of habitats do tapeworms live throughout their life cycle? Why can't they develop in one place?

2) How is this change of environment similar to that of humans?

3) What does the information about the environmental physiology shed insight upon about the tapeworm's nutrient regulation?

4) How is the information about regulation similar to that of the information about environmental sensing?

5) Also related to the previous two questions, how does the waste excretion contribute to the knowledge of tapeworms' regulatory systems? What can one conclude from this information?

__**Citations**__:

 * 1) Hillis, David M. “Animal Origins and Diversity.” Principles of Life, Sinauer Associates, 2012, pp. 457–470.
 * 2) http://animaldiversity.org/accounts/Taenia_solium/ (2)
 * 3) The Editors of Encyclopædia Britannica. “Tapeworm.” //Encyclopædia Britannica //, Encyclopædia Britannica, Inc., 18 Mar. 2014, www.britannica.com/animal/tapeworm.
 * 4) http://www.ucmp.berkeley.edu/platyhelminthes/platyhelminthes.html
 * 5) https://web.stanford.edu/group/parasites/ParaSites2001/neurocysticercosis/morphology.html
 * 6) https://www.britannica.com/animal/flatworm/Development
 * 7) http://www.hbwbiology.net/taxonomy-platyhelminthes.htm
 * 8) []
 * 9) http://www.biologydiscussion.com/invertebrate-zoology/phylum-platyhelminthes/taenia-solium-habitat-structure-and-life-history/28918
 * 10) https://www.britannica.com/animal/flatworm
 * 11) https://www.ncbi.nlm.nih.gov/pubmed/11952216?report=abstract
 * 12) http://animals.mom.me/sensory-structures-flatworm-7189.html

1) Because the different stages of the tape worm's life cycle requires different environments, it is unable to live in one stable environment throughout its life cycle.
 * __Review Questions (Answers)__:**

2) As tapeworms must grow and develop in one environment, humans must do the same. When a human is a fetus, it grows and develops inside the mother's uterus, and in the case of the tapeworm, it grows and develops in the intestine of its host. More specifically, when the tapeworm develops enough, it must change environments to stay alive; humans are born and live outside of their mother's body because gas exchange becomes insufficient at approximately 9 months of pregnancy. Obviously, both organisms do not stop growing and developing when the change environments; however, different conditions are required as the life cycle progresses.

3) Provided that the tapeworms died after a change in temperature, pH, and salt concentration, it is likely they these organisms do not have a system to regulate these conditions. Typically, organisms that have regulation methods can withstand a certain amount of change before they are unable to regulate the conditions further before dying, yet it appears that the tapeworms do not do the same.

4) Given both subtopics, it is obvious that these organisms are not very complex. Because they are unable to sense their environment, it can only make sense that they have no means of adjusting to their environment to maintain homeostasis.

5) Again, a very similar answer to those of the previous two questions will lend an explanation to this organism's regulatory abilities and systems. Considering the waste excretion happens through diffusion, the organism expends no energy maintaining its internal conditions. One might be able to conclude that this organism allocates most of its energy to reproduction and survival, especially in terms of nutrient acquisition (note the lack of the word homeostasis; clearly the organism has little to no control over its internal function and depends heavily on its environment to survive).