biotechnology lecture Platyhelminthes

Platyhelminthes • Platyhelminthes are worms with small, soft body • Including: + Free – living: flatworms (Turbellariac); + Parasitic: flukes (Trematodac) and tapeworms (Cestodac) Turbellaria Trematoda Cestoda Key characteristics: • Exhibits bilateral symmetry: Only one plane of bisection produces left and right mirror image halves of body; • Polarized along two perpendicular axes: anterior-posterior (head-tail); dorsal-ventral (back-belly) axis • Triploblastic animal: - Three germ layers: Ectoderm, mesoderm and endoderm - Mesoderm contributes to form true muscle tissue • Unsegmented worms • Digestive organ with several degrees of development • Excretory organ: protonephridia • Platyhelminthes lack: - Coelom: a fluid filled cavity or canal lined by mesodermderived epithelium - Hemal system: a specialized part of connective tissue compartment that consists of interjoined vessels and cavities through which the blood circulates - Cuticle: mainly composed of α-chitin and protein → uncomplicated anatomy except for a complex reproductive system • Consist of about 20.000 species identified • Include : - Free-living flatworm (Turbellaria) - Parasitic taxa (fluke: Trematoda; Monogenea; Tapeworm: Cestoda) Turbellariac • Turbellaria could be found in marine, fresh water • Most of them are bottom dwellers, benthic inhabitants, few are pelagic • Other taxa are terrestrial, confined in humid areas • Size of body: changed upon species, from approximately 0.5 cm to 60 cm (Macroturbellarians: Remacephalus arecepta, found in Baikal lake) Body Wall • Outer of body is covered by epidermal layer with many cilia • Few taxa, epidermis is syncytial (without cell partition/septum) • Beneath the epidermis is basal lamina or basement membrane with the function of supporting the body wall • Epidermis contains gland cells, either entirely within epidermal layer or below muscle layers • Gland cells secrete: adhesive, mucus and other substances • Typical secretion of Turbellarians is rhabdoids - rodshaped secretions - Rhabdoids are released by gland cells to the surface of the epidermis where they expand to form mucus - Most common kind of rhabdoid is rhabdite with functions of locomotion, cocoon formation, predator repellant Turbellaria rhabdites Trematoda c (tiep) Parasitic flatworms, including Digenea sc, Aspidogastrea sc Key features: - 11.000 species, endoparasite; body size: 0.2 mm-6.0 cm, dorsoventrally flattened (leaf shape) - Body structure: in many respects similar to turbellarians, such as alimentary, reproductive, excretory, nervous, musculature and parenchyma systems Human liver fluke Clonorchis sinenesis - A major difference is in the tegument, epidermis of which is a nonciliated, syncytial layer called neodermis Development original of the neodermis: As the infective laval stage (miracidium) of the parasite penetrates the body wall, it slought off its epidermis and replaces it, from below, with syncytial neodemis derived from parencymal cells - Development of the organ for adhesion: suckers, oral and ventral suckers - Increasing the reproductive capacity Oral sucker Ventran sucker - Life cycle includes two or more hosts which account for the name Digenea - The first intermediate host: snail; the second, if happend: Arthropod or fish; the final or definitive host: vertebrate, human Life cycle of F hepatica - General life cycle consists of following stages: Zygote → miracidium larva → sporocyst → redia → cercaria → metacercaria → adult Some representative species of Digenea: Clonorchis sinensis (Sán gan nhỏ) Eurytrema pancreaticum (Sán tụy) Fasciola hepatica (Sán gan lớn) Fasciolopsis buski (Sán ruột) Paragonimus ringeri (Sán phổi ) Schistosoma (Sán máu) Monogenea c - 1100 species, 1-20 mm length, ectoparasite, most attach to the skin - Having only posterior attachment organ-haptor (bearing suckers and/or hooks) - Life cycle differs from that of Digenea: there is no intermediate host; clonal reproduction is absent (monogenea = one generation) Cestodac • 3400 species, endoparasites in the gut of vertebrate, some m- 25m length • Ribbonlike adult body, devided some parts: - Scolex adaptes for attachment to the host - Narrow neck (growth zone) - Segmented trunk or strobila, each is called a proglottid - Depending the developmental level, the shape of the proglottid may be different from each other Tapeworm in Intestine of dog Life cycle of tapeworm Summary Triploblastic: Three germ layers Bilateral symmetry; definite polarity of anterior and posterior ends, body flattened dorsoventrally Epidermis may be cellular or syncytial (ciliated in some); Muscular system of mesodermal origin; layers of circular, longitudinal, and sometimes diagonal fibers No internal body space other than digestive tube (acoelomate); spaces between organs filled with parenchyma, a form of connective tissue or mesenchyme 6.Digestive system incomplete (gastrovascular type); absent in some Nervous system consisting of a pair of anterior ganglia (brain) with longitudinal nerve cords connected by transverse nerves; Simple sense organs; eyespots in some Excretory system of two lateral canals with branches bearing flame cells (protonephridia) 10 Most forms monoecious; reproductive system complex, usually with well-developed gonads, ducts, and accessory organs; internal fertilization; development direct in free swimming forms;indirect in internal parasites; life cycle often involving several hosts ...• Platyhelminthes are worms with small, soft body • Including: + Free – living: flatworms (Turbellariac);... worms • Digestive organ with several degrees of development • Excretory organ: protonephridia • Platyhelminthes lack: - Coelom: a fluid filled cavity or canal lined by mesodermderived epithelium