Platyhelminthes BIO 205 PDF

Phylum Platyhelminthes (Flatworms & co) Chapter 8  METAZOA Bilateria Protostomia Deuterostomia...

Phylum Platyhelminthes (Flatworms & co) Chapter 8  METAZOA Bilateria Protostomia Deuterostomia Lophotrochozoa Ecdysozoa choanofla gellates sponges cnidarians molluscs annelids flatworms nematodes arthropods echinoderms chordates Gastrulation Diploblasty Multicellularity Blastulation  Bilateria Animals actively looking for food, shelter, and sexual partners – Need for strategies and structures – Radial symmetry NOT appropriate – 2 major innovations: Cephalization & central nervous system – Concentration of sensory organs in the head region Bilateral symmetry  METAZOA Bilateria Protostomia Deuterostomia Lophotrochozoa Ecdysozoa choanofla gellates sponges cnidarians molluscs annelids flatworms nematodes arthropods echinoderms chordates (Org. & Syst. level) Gastrulation Bilateral symmetry Diploblasty Cephalization Triploblasty Multicellularity Blastulation Phylum Platyhelminthes Acoelomate: body cavity filled with parenchyma Muscle cells and parenchyma derived from mesoderm Triploblastic  METAZOA Bilateria Protostomia Deuterostomia Lophotrochozoa Ecdysozoa choanofla gellates sponges cnidarians molluscs annelids flatworms nematodes arthropods echinoderms chordates Mouth formed from blastopore, etc. (Org. & Syst. level) Gastrulation Bilateral symmetry Diploblasty Cephalization Triploblasty Multicellularity Blastulation Lophotrochozoa Phyla: Phyla: ex. Ectoprocta - Molluscs (NOT covered in BIO205) - Annelids - Platyhelminthes Lophophores Trochophore larvae  METAZOA Bilateria Protostomia Deuterostomia Lophotrochozoa Ecdysozoa choanofla gellates sponges cnidarians molluscs annelids flatworms nematodes arthropods echinoderms chordates Trochophore larva Mouth formed from blastopore, etc. (Org. & Syst. level) Gastrulation Bilateral symmetry Diploblasty Cephalization Triploblasty Multicellularity Blastulation Phylum Platyhelminthes “Flat worms” 20-30K species Marine & freshwater but some terrestrial Many endoparasites Phylum Platyhelminthes “flat worms” Great surface / volume ratio Appropriate for gas exchange, nutrition and wastes management Phylum Platyhelminthes Synapomorphy: lamellate rhabdites (rod-shaped structures that swell when discharged in water to form a mucus coating) Role: locomotion & gas exchange  Platyhelminthes Lamellate rhabdites Phylum Platyhelminthes What’s new? Excretory/ osmoregulatory system Copulation and copulatory organs Cephalization & Central nervous system Phylum Platyhelminthes What’s new? Excretory system / osmoregulation Cephalization & central nervous system Copulation Phylum Platyhelminthes EXCRETION: elimination of metabolic waste products (such as ammonia, urea and uric acid) OSMOREGULATION: maintenance of stable internal solutes concentrations, regulation of osmolarity (total amount of solutes in a solution) Excretion and osmoregulation are often linked, since nitrogenous wastes are important (and usually toxic) solutes In sponges and cnidarians, these are dealt with mainly at a cellular level but most bilaterally symmetrical animals need a system to collect metabolic waste and/or regulate amount of water in tissues  Phylum Platyhelminthes Vertebrates Invertebrates 300 mOsm/L 1 000 mOsm/L Fresh water Salty water < 50 mOsm/L (marine or sea water) 1 000 mOsm/L 1 000 mOsm/L Planaria  Phylum Platyhelminthes Platyhelminthes living in fresh water need a system to regulate the amount of water (and solutes) in their tissues Fresh water < 50 mOsm/L 1 000 mOsm/L Planaria  Osmoregulatory system Protonephridia: network of tubules capped by flame cells inside and opening outside by a nephridiopore Primary role: Protonephridial à Remove excess water (especially system in freshwater) Secondary role: à Excretion of ammonia In Platyhelminthes, NH3 is primarily excreted by diffusion through body wall Phylum Platyhelminthes What’s new? Excretory system / osmoregulation Cephalization & central nervous system Copulation Central nervous system Cephalization: Sensory Ocellus reception (ocelli and chemoreceptors) on the head Phylum Platyhelminthes What’s new? Excretory system / osmoregulation Cephalization & central nervous system Copulation Direct contact between 2 individuals to transfer sperm from the body of the ‘male’ to the body of the ‘female’ Internal fertilization  Reproductive system With copulatory organs Platyhelminthes are Monoecious Physiology Respiratory ‘system’? Diffusion through body surface Mucus = humid (terrestrial organisms) Skeletal ‘system’? Muscles et parenchyma Circulatory ‘system’? None… but surface area optimized for many ‘systems’ Phylum Platyhelminthes Acoelomate Triploblastic Osmoregulatory system Copulatory organs Cephalization and CNS Gut present (blind) or absent Phylum Platyhelminthes Four groups (3 covered in BIO 205): Turbellaria grade (flatworms) Class Trematoda (flukes) Class Cestoda (tapeworms) Figure 8_02 Paraphyletic group (grade) Phylum Platyhelminthes Grade Turbellaria 29 Grade Turbellaria (flatworms) Mostly free-living scavengers and predators, 50-500 mm NOT parasites Typically creep along substrate using mucus and ventral cilia Grade Turbellaria (flatworms) Mostly free-living scavengers and predators, 50-500 mm Typically creep along substrate using mucus and ventral cilia Epidermis: formed by rhabdite cell & cilia Digestive and nervous systems No anus Cephalization Primitive CNS  Grade Turbellaria Ocellus Sensory reception: ocelli and chemoreceptors on the head Phylum Platyhelminthes Grade Turbellaria 34  Reproduction Copulatory organs Grade Turbellaria (flatworms) Reproduction and life cycle Sexual reproduction Monoecious Usually practice cross-fertilization Asexual reproduction fission, fragmentation and regeneration Simple life cycle with direct development (immature instead of larva) Videos Planarian, eating http://www.youtube.com/watch?v=w0QzSYQGsnA&feature=related Terrestrial planarian, moving http://www.youtube.com/watch?v=Fq_aSR5FK0Y&feature=fvw http://www.youtube.com/watch?v=NgkFnY3aaX4 Fission http://www.youtube.com/watch?v=E1d9MyJBLlg&feature=related Members of Neodermata are all endoparasitic  Platyhelminthes : Clade Neodermata Endoparasites àComplex life-cycles Need to pass through specific sequences of 2 or more hosts to complete life cycle In intermediate host(s): Worms are immature ØNo sexual reproduction ØAsexual reproduction (in some species) In definitive host: Worms are mature (adults) ØSexual reproduction Platyhelminthes : Clade Neodermata Endoparasites àImportant adaptations: Penetration glands Hooks ↑ reproductive capacity Epidermis : NOT ciliated Loss of rhabdites Syncytial tegument Epidermis/tegument Promotes nutrient, wastes and gas exchanges Protects against digestive enzymes Epidermal cell Microvilli (cytoplasm) Muscles Parenchyma Rhabdite cell Tegumentary cell Non ciliated covering Cellular ciliated epidermis Syncytial tegument Turbellaria All other classes Class Trematoda Leaf-like form, relatively similar to turbellarians BUT… All endoparasitic… Anterior adhesive organ : suckers and hooks socio-economically devastating parasites Body design reflects adaptations to parasitism Life cycle involves both sexual and asexual reporduction Ex. 1 Clonorchis sinensis, Chinese liver fluke Definitive host (monoecious) Second intermediate host First intermediate host  egg 1 Up to 250 000 àMany different immature stages àMuch asexual replication 1 egg à 1 miracidium à 1 sporocyst à many rediae à many cercariaeà 1 metacercaria per cercariaà 1 adult per metacercaria Endoparasites Ex. 2 Schistosoma mansoni, Blood fluke Definitive host intermediate host 48 Class Cestoda Tapeworms All endoparasitic- adults infect gut of vertebrates Syncytial tegument (like trematodes) Intermediate hosts: vertebrates or invertebrates Monoecious Some very large (>8m.) Class Cestoda Basic body plan: Scolex, attachment device (suckers and hooks), NOT head! Strobila Continuous growth behind scolex Made of many proglottids Each proglottid is fully reproductive Self-fertilization common microvilli tegument  Each proglottid is fully reproductive Self-fertilization common microvilli No mouth, no digestive system How do they feed? tegument  Definitive host Beef tapeworm Scolex Taenia saginata Scolex “bladder worm” Shelled larva hatches in cow stomach, burrows in blood vessel and migrates to Intermediate skeletal muscles where it forms a cyst host Beef tartare anyone?  Eaten by human Definitive Intermediate host Pork tapeworm in raw/ rare pork host Taenia solium Cysts in human muscles and organs Cysticercosis Caused when humans eat eggs of T. solium and become an intermediate host instead of a definitive host Self-infection is common Cysticerci develop in any organs such as muscles, brain, eyes, livers, spinal cord, etc. à can cause Cysts in muscle Intermediate extensive damage (“measly pork”) host Eggs on ground ingested by pork Cysticercosis Cysticerci infection (cysticercosis) from pig tapeworm, Taenia solium Cysticercosis Human brain infected with cysticerci of pig tapeworm, Taenia solium Cysticerci infection causes much more damage than tapeworm infection Class Cestoda Asexual reproduction is rare but does occur in a few taxa. Massive size range Whale tapeworm can reach 30 m 3-6 mm Echinococcus granulosus from dog 8.8 m Diphyllobothrium nihonkaiense isolated from a human Grade Turbellaria Class Trematoda (flukes) Free-living Endoparasite Cellular epidermis Syncytial tegument (no rhabdites) Rhabdites Complex life cycle with 2+ hosts Simple life cycle 1 egg = many adults Many harmful to humans Class Cestoda (tapeworms) Endoparasite Syncytial tegument (no rhabdites) Complex life cycle usually with 2+ hosts Massive egg production 1 egg = 1 adult (usually) Some harmful to humans