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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>.
