Transcript Acoelomates
Acoelomates Phylum Platyhelminthes Phylum Nemertea Phylum Gnathostomulida Taxonomy Grade Bilateria Division Protostomia Type title here Acoelomates Example: Platyhelminthes Pseudocoelomates Example: Nematoda Division Deuterosomia Eucoelomates Examples: Mollusca, Arthropods, Annelida Examples: Echinodermata, chordata Acoelomate Phyla • Platyhelminthes – Flat worms • Nemertea – Ribbon worms • Gnathostomulida – Jaw worms Why bilateral symmetry? Movement toward prey or host – Cephalization – Directional sense organs • Chemoreceptors • Ocelli (light sensing eyespots) • Rheoreceptors (sense water currents) Acoelomates Key Features • Three germ layers – Ectoderm, endoderm, mesoderm – Mesoderm forms muscle and mesenchyme • Organ-system level of organization – Cephalization – Excretory system – Some have circulatory and one-way alimentary canal Acoelomates Body Plan Phylum Platyhelminthes • Specialized Cells – – – – Rhabdites - secrete mucous sheath Tegument - outer covering of syncytial cells Flame cells – Osmoregulation Some have endolecithal egg cells – yolk contained within egg cell Platyhelminthes Cross Section Tegument • Syncytium – Apical cell membrane missing Flame Cell • Osmoregulation – Beating flagella creates negative pressure to draw fluid into chamber – Water is directed through channels then through an external pore Major Classes of Platyhelminthes • Class Turbellaria – Planaria – free living • Class Trematoda – Liver flukes – endoparasites • Class Monogenea – Fish ectoparasites • Class Cestoda – Tape worms – endoparasites Class Turbellaria • Key Features – – – – – Ladder like nervous system Eye spots (Ocelli) Auricles - chemoreceptors Free living flatworms Muscular and ciliary movement – Carnivorous Planarian Body Plan Class Trematoda • Similar in structure to Turbellaria • Special adaptation for endoparasitic life style – Cyst glands – Suckers and hooks for griping host • Digenetic – complex life cycle with multiple hosts Liver Fluke Liver Damage Caused By Flukes • Scar tissue • Blocked bile ducts Flukes in Liver Section Fasciolopsis - Anterior End Schistosoma mansoni • Blood fluke • Male and female are dioecious Schistosoma cercaria Class Cestoda • Tapeworms - endoparasites • Key Features – Lack a digestive system – Composed of reproductive units called proglottids – Adult tegument covered in microvilli-like projections – increases surface area, non-ciliated Tapeworm • New proglottids are added just behind the scolex Tapeworm Tegument • Microvilli help with food adsorption • Sensory cells – no other sense organs Mature Proglottid • Reproductive unit • Mature proglottids are either shed or produce shelled embryos • Each proglottid has both male and female organs Tape Worm Life Cycle Taenia solium Pork tapeworm Taenia Cyst in Muscle Phylum Nemertea • Ribbon worms – Ciliated epidermis – Locomotion – gliding over slime track and muscular contraction – Complete digestive tract – mouth and anus – Extracellular digestion – Proboscis to capture prey Amphiporus