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

Classes of Platyhelminthes Cestoda-beef & pork tapeworms

Classes of Platyhelminthes Monogenea- Diplozoon paradoxum

Classes of Platyhelminthes Trematoda-Human Live Fluke

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

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. Circulation

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 Excretion

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

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

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 Movement

General –Asexual reproduction Budding Binary fission Regeneration –Sexual reproduction Hermaphroditic Occurs through the exchange of sperm Internal fertilization Cross fertilization Reproduction

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 "Platyhelminthes." Oracle ThinkQuest Library. Web. 21 Apr "Behavior and Reproduction." Monogeneas. Web. 21 Apr