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PHYLUM PLATYHELMINTHES, (Gt. platys, , =, , flat; helmins, , =, , worms) (FLAT WORMS), , There, , about 13,000 species of flatworms., , are, , CLASSIFICATION OF PLATYHELMINTHES FOR, COMPETITIVE EXAMINATIONS, , Characters, 1. Body is either, , lat., 2. These, , are, , leaf-like or ribbon-like dorsoventrally, , first animals to have, , organ-level, , It is divided in three classes on the basis of body, mouth position and habitat., A. Class Turbellaria (L. turbella = stirring). (i) Body, , shape,, , organisation and bilateral symmetry. These have blind, , is leaf-like and, , sac body plan., , ventral side of middle of body and pharynx is protrusible., and acoelomate animals., , ii), , Spaces between the body organs are filled with, a mesodermal connective tissue, called parenchyma., , by a, , mostly parasitic but some are, free living (turbellarians). Parasitic forms have hooks, , Dugesia., , 3. These, , are, , triploblastic, , 4., , 5. Habitat. These, , are, , their host., 6. Excretion and osmoregulation occur by peculiar, cells called flame cells or protonephridia or solenocytes, (Fig. 11 A). These are ammonotelic., and suckers for adhesion, , 7. Gut. These have, , on, , incomplete alimentary canal., , 8. Nervous system. It is ladder-like (Fig. 11B)., 9. These are first animals to show cephalization., , 10. Reproduction. These are mostly hermaphrodite., rertilization is internal and may be self or cross-, , fertilization. Development includes larval stages so is, , nairect. Turbellarians undergo asexual reproduction, by transverse fission., 1.Planarians have very high power ofmorpholactic, , regeneration., , These, , are, , ciliated, These, , unsegmented. (ii), , Mouth, , free-living. (iv) Body, , is, , commornly, , called, , present, , externally, , epidermis but there is no, , are, , is, , on, , covered, , cuticle., , planarians, , e.g. Planaria,, , B. Class Trematoda (Gr. trema. = hole; eidos = form). (i), , Mouth is present, ecto- or, on anterior end of body. (i) These are either, is externally covered with a living, endoparasites. (iv), , Body is leaf-like and unsegmented. (i), Body, , tegument produced into spinnules., , These are commonly called flukes eg., Fasciola (Sheep, , liver-fluke),, , Schistosoma, , (blood fluke),, , etc., , C. Class Cestoda (Gr. kestos = girdle; eidos = form)., , is ribbon-like and divided into segments calledd, proglottids. (i) Mouth and alimentation absent so absorb, the nutrients through their body surface. (ii) These are, endoparasites, (iv) Body is externally covered with, , (i) Body, , only, , a living tegument but with no spines., These, , are, , commonly, , called tapeworms e,g., Taenia, , solium (Pork tapeworm) and T. saginata (Beef tapeworm).

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Parasitic adaptations in Flukes and Tapeworms:, 1. Absence of epidermis and presence of, resistant horny cuticle on the body wal., , tough, , CYTOPLASMIC, , LONGITUDINALBRAIN, , PROCESSES, , and, , NERVES OR, , NERVE CORDS, LATERAL, , NUCLEUS, , BASAL, , are either, 2. The sense organs like eye-spots, reduced or absent., like suckers, 3. These have some adhesive structures, , NERVES, , GRANULES, , TRANSVERSE, VACUOLES, , or hooks or both or other structures., , COMMIsSURES, , D>>cILIA, , 4.One or more intermediate hosts in thelife history, to reduce their period of exposure., , CAPILLARY, , 5. Absence of organs of locomotion., , DUCT, FLAME CELL, , 6. Alimentation absent in tapeworms., , B, , A, , Examples (Fig. 12): Taenia (Tapeworm), Fasciola, Planaria., (Liver fluke), Echinococcus (Dog tapeworm) and, , Fig., , NOUs, STE, , 11. Important characters of Platyhelminthes., , Table 10. Differences between Planarians, Flukes and Tapeworms., , 1., 2., , Body form, Position of mouth, , 3. Mode of living, 4. Body covering, 5. Examples, , Tapeworms, , Flukes, , Planarian, , Characters, , Ribbon-like and segmented., , Leaf-like and unsegmented., , Leaf-like and unsegmented., , On middle of ventral side of, , On ventral side, , body., Free-living, , of body., , Ectoparasitic or endoparasitic., , Always endoparasitic., , Ciliated epidermis., , Spiny cuticle., , Non-spiny cuticle., , Planaria, Dugesia, etC., , Fasciola, Schistosonna, etc., , Taenia, Hymenolepis, etc, , of anterior end, , SCOLEX, EYE-, , ROSTELLUM, , HOOKS, , SUCKER, , AURICLE, , Absent., , DORSAL SURFACE, NECK, , VENTRAL SURFACE, PHARYNGEAL-, , MOUTH, , POUCH, , HOOKS, , GONOPORE, , PHARYNX, , SCOLEX, NECK, , IMMATURE SEGMENTS, , A. DUGESIA, HEAD LOBE, , MOUTH-, , MATURE, , ORAL SUCKER, , SEGMENTS OR, PROGLOTTIDS, , GENITAL APERTURE-, , VENTRAL SUCKER, , -STROBILA, , GRAVID PROGLOTTIDs, , EXCRETORY PORE, B. FASCIOLA HEPATICA, , Fig. 12. Important Flatworms., , C. TAENIA SOLIUM

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PHYLUM NEMATHELMINTHES OR, ASCHELMINTHESS, , 5. These are first animals to have straight and, complete alimentary canal. Pharynx is muscular and, , (Gr. 11ema = thread; helmins = worms), , tri-radiate. Intestine is non-muscular. So these have, , (Thread or roundworms), , tube-within-a-tube plan., , Characters, form. These are commonly called, roundworms or threadworms or bagworms (askos, bag) because the body is long, cylindrical, unsegmented,, thread-like with no lateral appendages. So their cross, 1., , Body, , =, , absent., , section is always circular., , 2. These have organ-system organization and, , bilateral symmetry., 3. These are triploblastic animals (Mesoderm is, present as scattered pouches between ectoderm and, , endoderm)., , 4. These, , are, , 6. Excretion. Excretory system is H-shaped and, intracellular called Rennett cell. These are ammonotelic., 7. Body wall is formed of outer cuticle of, keratin, syncitial (multinucleate) epidermis and, only longitudinal muscle fibres. Circular muscles are, , 8. Number of cells is fixed in every system of body, (Eutyly). These show auxetic growth., , 9. Nervoussystem.Itis formed ofa circumpharyngeal, nerve ring giving rise to anterior as well as posterior, nerves interconnected by connectives. So it is of ladder, , type., , pseudocoelomates., , Table 11. Differences between Flatworms and Round, , Characters, , worms., , Round worms, , Flatworms, , 1. Body form, , Dorsoventrally flattened., , Long and cylindrical., , 2. Body cavity, , Acoelomates., , Pseudocoelomates., , 3. Alimentary canal, , Absent or incomplete., , Complete., , 4., , Flame cell., , Rennet cell., , Excretory structures, , 5. Epidermis, 6. Sexes, 7., , Examples, , Non-syncitial and, , unilaminar, , Generally bisexual., Planaria, Fasciola, Taenia,, , or, , absent., , Syncitial epidermis., Always unisexual., , etc., , Ascaris, Wuchereria, Ancylostoma, etc.