Acoelomate Bilateral Animals PLATYHELMINTHES Chapter 14 Acoelomate Bilateral Animals PLATYHELMINTHES

Overall Characteristics Acoeolomate Only one internal space Bilateral Symmetry due to cephalization Triploblastic Three germ layers (formed during embryonic development) Middle mesodermal layer: parenchyma

Platyhelminthes: the classes 1. Turbellaria free living flatworms 2. Monogenea Most are ectoparasites 3. Trematoda flukes All are endoparasites 4. Cestoda tapeworms

I. Form and Function Most have Ciliated epidermis Epidermis (Tegument) syncytial (multinucleated) Basement layer separating epidermal from organ layers contains rhabdites Produce mucous

Muscle fibers below basement layer Dual-gland adhesive organs (turbellarians) Viscid gland = stick Releasing gland = release 1 Anchor cell

A. Nutrition and Digestion Mouth, pharynx & intestine (except cestodes) gastrovascular cavity branching

Mostly free-living & carnivorous detect prey by chemoreception Like smelling them! Extracellular digestion enzymes Intracellular digestion phagocytosis

B. Excretion & Osmoregulation Protonephridia Osmotic balance Some ammonia excretion (nitrogenous waste)…, but most by diffusion through body wall Flatworm kidney Made of flame cells Function: osmoregulation

C. Nervous System Brain Longitudinal Nerve cords Anterior Ganglia Bundle of neurons Longitudinal Nerve cords Sensory: collect info from environment Motor: action Association: link

D. Sense Organs 5 sense organs Mechanoreceptors - tactile (touch) Chemoreception - taste / smell, mates? Rheoceptors (H2O flow) Statocysts - balance Ocelli - simple vision

Turbellaria Polyphiletic (p. 302) Simple life cycles .5 to 50cm iin length Midventral mouth or proboscis (planaria) Not at anterior (head) end Muscular waves & or ciliary locomotion Gut varies from none to highly branched (correlates with size) Order Acoela (primative marine flatworms) only mouth, no gastrovascular cavity! Amazing regenerative abilities- planaria developmental studies

E. Reproduction Turbellarians (e.g.. Planaria) Endolecithal (yolk) and ectolecithal (no yolk) Embryos emerge as juveniles (similar to adults) Fission Monoecious = hermaphroditic Protostomes with spiral determinate cleavage cross fertilization Genital pore = vagina Oviduct, eva Cirrus = penis Testes, vas deferens

Reproductive System

III. Class Trematoda (flukes) Parasitic Vertebrate host and invertebrate Intermediate host Leaf-like Suckers (two) & or hooks Well developed alimentary canal Nervous system (non-sensory) Excretory system Reproductive system A. Subclass Digenea Mollusk intermediate Human definitive host Pass via excreta to H2O Infect many body systems Digestive Respiratory Urinary reproductive Circulatory system

B. Liver Fluke 1. All trematodes are parasitic flukes. 2. Most adults are endoparasites of vertebrates. Most sporocysts are endoparasites of invertebrates. 3. They resemble some Turbellaria but the tegument lacks cilia in adults. 4. Adaptations for parasitism include: a. penetration glands, b. glands to produce cyst material, c. hooks and suckers for adhesion, and d. increased reproductive capacity!!! 5. Sense organs are poorly developed. 250,000

Fluke life cycle Clonarchis (liver fluke) More Egg (Shelled miracidium) Miracidium (free swimming larva) penetrates first invertebrate host Sporocyst forms in host (asexual reproduction) Rediae from sporocyst which also reproduce asexually to create.. Cercariae which emerge from the intermediate host to become.. Metacercariae which infect another intermediate or final vertebrate host and mature, usually after ingestion Eg. Chinese liver fluke (monoecious) Multiplication 1 miracidium to 250,000 cercariae!!!

Be careful what you drink, eat, & where you wade! C. Schistosoma (blood flukes) Sexual dimorphism (dioecious) Male larger than female Snail Human (penetrates skin) 200 - 300 million people infected globally Multiple organ infection Sometimes fatal No rediae intermediate Cirrhosis of the liver (eggs) Image Lung Flukes Snails Crabs and crayfish Vertebrates (humans) Leucochloridium paradoxum snails and birds sporocyst Be careful what you drink, eat, & where you wade!

V. Class Cestoda Tapeworm Form Life Cycle Taenia saginatus (beef) Taenia solium (pork) Form Gutless wonders! Microtriches (tegument) Scolex Germinative zone Proglottids (Strobila chain) Life Cycle Monoecious Self fertilization (or not) Gravid proglottid Shelled larvae Consumed by intermediate Muscle cysts Bladder cysts (invaginated cysticercus) Hydatid cyst (dog tapeworm) Uncooked meat Definitive host consumes intermediate host Cysticercosis (ingestion of eggs or proglottids)

Class Cestoda 1. Tapeworms have a unique flattened and segmented shape compared to other flatworms. 2. Each trailing segment is a proglottid containing a set of reproductive organs. 3. The entire surface of cestodes is covered with projections similar to microvilli seen in the vertebrate small intestine; these microtriches increase the surface area for food absorption. 4. Nearly all are monoecious. 5. They lack sensory organs except for modified cilia. (Fig. 14- 17) 6. The scolex is a holdfast head portion with suckers and hooks.