pLaTyHeLmInThEs

بسم الله الرحمن الرحيم 
Assalamualaikum

platyhelminthes

 characteristics

> multicelled animals with elongated bodies that have clearly defined anterior (front) and posterior (rear) ends.

> bilaterally symmetrical, meaning that their two sides reflect each other

> usually have a recognizable head, which houses gravity and light-receptive organs, and eye spots

> lack circulatory and respiratory systems and and have only one opening serves as mouth and anus

> Their soft, flattened bodies are composed of three layers-the ectoderm, endoderm, and mesoderm. ( triploblastic )

> may be covered by a protective cuticle or by microscopic hairs, called cilia.

> internal organs are comprised of a nervous system, usually hermaphrodite sexual organs, and an excretory system  (protonephridia & nephridiopore )

> acoelomate : body comprised of parenchyma

Class Turbellaria

> These flatworms are covered by microscopic hairs (cilia) that they beat continuously, creating turbulence in the water-an activity that gave them their name

> most familiar Turbellarians are the planarians, soft-bodied, aquatic, flattened worms that appear to have crossed eyes and ear lobes. 

*the crossed eyes are eye spots with which the worm can detect light.

 *The lobes to each side are sensory and also are equipped with glands to secrete an adhesive substance used in capturing prey.

> The single opening on the ventral (bottom) surface of the worm serves as both mouth and anus.

 > Internally the worm has a complex, branching gut that courses nearly the full length of the body.

> Since the worm has no circulatory system, the elongated gut brings food to nearly all areas of the worm's body

> Planaria have no skeletal or respiratory systems.

> Turbellarians have no cuticle

> All turbellarians are simultaneous hermaphrodites, having both female and male reproductive cells, and fertilize eggs internally by copulation.

**REPRODUCTION 

>Freshwater planaria-mostly reproduce sexually- oviparous , some- parthenogenesis

> Families Dugesiidae & Planariidae occasionally reproduce by binary fission

> Many turbellarians clone themselves by tranverse or longitudinal division

> Regeneration

*If a planaria is cut in half, the front half will grow a new tail section and the rear half will generate a new head. 

*If cut into thirds, the middle third will regrow a head and tail and the other two sections will regenerate as described.

**DEFENSE

> Camouflage - to avoid being seen by an predators

> Bright colouration - warn predators of toxin / distasteful chemicals = aposematic colouration 

>  Aposematic coloration protects animals from predators by producing a"warning signal" from the combination of color patterns which they demonstrate.

 > The "warning signal" identifies an animal as unpalatable, or distasteful to the inquisitive predator.

>  It is believed that before warning coloration developed, a chemical defense system was first established in animals.

Class Monogenea

> parasites, completing their life cycles within the body of a single living host, such as fish, frogs, turtles, and squid.

> Most of the 400 species in this class are ectoparasites, meaning that they cling to the outside of their host, for example, to the gills, fins, or skin of fish.

> Their bodies are covered by a protective cuticle and have adhesive suckers at each end.

> Body - head,trunk,haptor ( hook & suckers )

> They eat by sucking blood through their mouths, which open beside their suckers.

> has no eyespots ( no need light receiver )

 * some parasitic have eyespots because they live at the outer which receive the light

Class Trematoda

> Commonly known as flukes,

> Leaf-like form

>  Adaptation for parasitism :-

* various penetration of glands*glands to produce cyst material

*adhesion organs - suckers & hook

*increased reproductive capacity

*mouth at the anterior end,with oral sucker

*sense organ poorly developed

**LIFE CYCLE

>A fluke must live in two or more hosts during its lifetime because its developmental needs are different than its adult needs 

* The first host is usually a mollusk and the final host-which houses the fluke during its mature, sexual stage-is invariably a vertebrate, sometimes a human. 

> Egg : miracidium,sporocyst,redia,cercaria,metacercaria,adult

** Blood flukes, called schistosomiasis, 

- 2 host ( snail & human)

- Eggs in intestinal wall cause abdominal pain, ulceration, abcesses , & bloody diarrhea

- Eggs block organs

________________________________________________________________________

** Liver fluke in human , Chlonorchissinensis(in raw fish/ undercooked fish )

- Intermediate host 1- snail Parafossarulus, tissue to liver 

- Intermediate host 2 - fish family Cyprinidae,bore under scale to muscle

- Adult habitat : bile duct of fish eating mammals

- Symptoms : abdominal pain,liver cancer,jaundice

Worms mature & produce egg -> Eggs passed in feses into water -> Miracidium hatches from egg,infects snail ( 1st intermediate ) -> Cercariae exit from snail -> Cercariae penetrate the skin of fish, 'encyst' in fish muscles as metacercariae-> Human infected by eating raw / undercooked fish ->Metacercariae 'excyst' in small intestine & immature worm migrates into bile ducts of the liver 

*berterusan.. hihi

Class Cestoda

> Tapeworms are the dominant member 

> Long flat bodies with linear series of sets of reproductive organs ( 1 set - 1 proglottid )

> Tapeworms cling to the intestinal wall of their hosts with suckers, hooks, or other adhesive devices.

> No digestive sysem- Having no mouth or gut, they receive their nourishment through their skin.

>  Entire surface covered with microtriches -minute projection for nutrient absorption

> Body : scolex,neck,strobila

> Specialized structure - scolex (attachment organ.normally with hook & suckers) 

 * function - for attachment to the host,no suck of nutrients

** Taenia sp.

- T.saginata - beef tapeworm

- T.solium - pork tapeworm ( both juvenille & adult can develop in humans )

*adult - in human intestine

*Juvenille (cysticerci ) in intermuscular tissue of cattle,pigs

-Scolex - with sucker no hook

-Short necks connect scolex & strobila ( up to 2000 proglottids )

**CYSTICERCOSIS

- Cysticercus cellulosaein pigs

- intermediate stage of Taenia solium- longer than T.saginata in the small intestine of humans - no health implication

- In humans, auto-infection can occur from adult worm* most frequently affected site is central nervous system - brain- neurocysticercosis - may lead to epilepsy (sawan )

LIFE CYCLE

- After 2-3 months of cysticercus in pigs ,pearly white cyst with an invaginated scolex move to muscles

- The ingestion proglottides by scavenging pigs - transmission of cysticerci to swine

* example : use of human excrement as fertilizers

- Larvae hatch from eggs in intestine - migrate to muscle tissue,brain,liver & ...

- The auto-infection  of the central nervous system with the larva form of cysticercus in humans is manifested with headache,dizziness,hydrocephalus,loss of vission & nausea

* mohon ditegur y salah :)




 والسلام