Transcript Classes of Platyhelminthes

General Characteristics
• flattened, bilaterally symmetrical
• have no other body cavity than the
digestive cavity (acoelomates)
• platy = flat & helminthes = worms
• Platyhelminthes were regarded as
a primitive stage in the evolution of
bilaterians soft and ciliated
epidermis covered with cuticle and
external suckers or hooks, or both
• space between internal organ filled
by loose parenchyma
• well developed muscle layers
• no skeletal, circulatory, or
respiratory system
Classes of Platyhelminthes
Turbellaria-Planaria
http://www.thaigoodview.com/library/contest2551/science04/119/kingdon_animalia/Class%20Turbellaria.htm
Classes of Platyhelminthes
Cestoda-beef &
pork tapeworms
http://x3on.blogspot.com/2009_04_01_archive.html
Classes of Platyhelminthes
MonogeneaDiplozoon
paradoxum
http://instruction.cvhs.okstate.edu/jcfox/htdocs/Disk1/Images/Img0086.jpg
Classes of Platyhelminthes
Trematoda-Human
Live Fluke
http://gurungeblog.wordpress.com/2008/11/11/mengenal-phylum-platyhelminthes/
Body Plan
• Bilateral symmetry
• have no other body cavity than the
digestive cavity (acoelomates)
• three germ layers (mesoderm, ectoderm,
endoderm)
• soft and ciliated epidermis covered with
cuticle and external suckers or hooks, or
both
Feeding
• General
– flat worms have one digestive opening that branches
to all parts of the body
• Turbellarians
– use muscular pharynx and prey on smaller animals or
feed on dead animals
• Cestoda
– block the intestines and rob nutrients from the human
host
• Monogena and Trematoda
– use suckers for attaching to internal organs rely on
the host for digestion
Respiration
• General
– Respiration occurs through diffusion
– Mainly carnivorous and prey on small
invertebrates
– Also feed on remain of dead animal
– All exchange is on a cellular level, by
diffusion, which is why flatworms are flat.
Nitrogenous waste mostly as ammonia, lost
through diffusion. Endoparasitic forms often
rely on anaerobic metabolism
Circulation
• General
– Circulation occurs through diffusion
– Lack circulation system
– Some species have gastrovascular system
– Otherwise, all internal transport occurs by
simple diffusion through and between cells of
the small body.
Excretion
• General
– Excretion occurs through flame cells
– Mouth: anterior end or mid-body on ventral surface
– Lack an anus
• Excess water (and possibly wastes) enters the flame
cell system and is propelled through the tubules toward
the outside by the beating of the cilia (the "flame
Response
• General
– Higher temperature and starvation
• Negatively affect size
• Decrease the number of days that elapsed
before egg laying began
• More larvae at 21°C than at 30°C
– Tangoreceptor: respond to touch
• Minimal b/c no orientation to light or gravity
– Light sensitive eyespots
– Can adapt and modify
Response II
– Ocelli
• eyespots that detect light
– Gangalia
• main sources of sensory input
– Aurical
• tasting chemicals
– Have a cephalized nervous system
• ventral nerve cord
• head ganglion attached to nerve cords
connected body
• by transverse branches across the
Movement
• Turbellians
– use cilia to move over a secreted slime tract
– head slightly raised
• Cestoda
– absorb nutrients from host
– no movement
• Monogenea and Trematoda
– parasitic worms rely on the host's circulation
– suckers for attachment
Reproduction
• General
– Asexual reproduction
• Budding
• Binary fission
• Regeneration
– Sexual reproduction
• Hermaphroditic
• Occurs through the exchange of sperm
• Internal fertilization
• Cross fertilization
Reproduction II
• Turbellaria
– exchange of sperm
• Cestoda
– proglottids: several ovaries and 1,000 distinct
testes
• Monogenea
– make both sperm and eggs
• Trematoda
– gut and well-developed reproductive system
Works Cited
• "Platyhelminthes." W. Fielding Rubel School of Business. Web. 21
http://cas.bellarmine.edu/tietjen/images/platyhelminthes.htm
• "Platyhelminthes." Oracle ThinkQuest Library. Web. 21 Apr. 2010.
<http://library.thinkquest.org/26153/marine/platyhel.htm>.
• "Behavior and Reproduction." Monogeneas. Web. 21 Apr. 2010.
<http://animals.jrank.org/pages/1521/Monogeneans-MonogeneaBEHAVIOR-REPRODUCTION.html>.