Phylum Platyhelminthes 4 principal types of flatworms divided into 4 taxonomic Groups Class Turbellaria >3,000 free-living spp some commensal a few parasitic forms Aquatic, few on land Body architecture adapted to a free-living lifestyle

Class Monogenea ~ 400 spp mostly ectoparasites of fish, amphibians. P Feed on blood, mucus.. Anterior and posterior ends for clinging, but life cycle remains simple, with a single free living larval stage P haptors A

Class Trematoda: flukes > 6000 spp of endoparasites (liver, lungs, blood, muscles) Body and life cycle adapted to parasitic existence. Ventral sucker Oral sucker

Class Cestoda: tapeworms > 3500 spp of endoparsites, almost all intestinal parasites with highly specialized body and life cycle. scolex 9 ft tapeworm from human host Largest in sperm whale was over 30 meters long

There is currently a debate between scientists about the position of comb jellies and sponges in the tree of animal life. What is the basis for this debate, and why is it important to our understanding of the evolution of several important animal organ systems?

Characteristics of the Phylum Bilateral symmetry Triploblastic

Characteristics of the Phylum Bilaterally symmetry Triploblastic Unsegmented Acoelomate

Characteristics of the Phylum Bilaterally symmetry Triploblastic Unsegmented Acoelomate Organ Systems Digestive System

Characteristics of the Phylum Bilaterally symmetrical Triploblastic Unsegmented Acoelomate Organ Systems Excretory System W/ Ultrafiltration and selective absorption

Characteristics of the Phylum Bilaterally symmetrical Triploblastic Unsegmented Acoelomate Organ Systems Complex reprod. System Regenerative capacities

Most Widely Accepted Phylogeny of the Major Flatworm Classes Cestoda (endoparasitic) Monogenea (ectoparasitic) Neodermata Trematoda (endoparasitic) Turbellaria -- Parasitic groups considered to be monophyletic and constitute a grouping known as the Neodermata Synapomorphies: new skin, obligate parasitism, protonephridia from two cells No synapomorphies for the phylum; thought to be polyphyletic? Introduce parasites here: Includes two groups of endoparasites and one ectoparasitic group. Endoparasism twice or lost? Synapomorphies of allparasites Challenges of Endoparasitism

Problems Posed by Endoparasitic Existence

Problems Posed by Endoparasitic Existence Reproduce and get embryos out of the host Contact new, appropriate host and obtain entrance Locate appropriate environment in the new host Maintain position in the host, withstand often anaerobic conditions and attack by immune system Avoid killing the host, at least until reproduction has been completed

In all Neodermata, epidermis is shed, and replaced by a syncitial tegument.

The body wall is a tegument with extensive microvillar surface area Monogenean tegument Cestode tegument

Advantages to having a tegument?

Class Cestoidea: primarily the tapeworms Body in segments called proglottids -formed behind the small head and continue to grow until released Mouth, digestive system lacking Scolex attachment structure Tegument highly folded with microvillar extensions Hermaphrodites Intestinal Parasites, commonly on vertebrates

Reproduction is primarily sexual Relatively simple Passive dispersal Reproduction is primarily sexual oncosphere

Cystecercoids (especially from the pork tapeworm Taenia solium) can accidentally end up in other parts of a body, especially in accidental hosts such as humans when they ingest eggs

Reproduction is primarily sexual Relatively simple Passive dispersal Reproduction is primarily sexual oncosphere

oncosphere

Hydatosis of the Liver

Class Trematoda: all endoparasites in blood, liver, gut distinguished by presence of ventral sucker (acetabulum), mouth and highly branched G-V Cavity Usually 2 intermediate hosts, at least one being a mollusc; the final host is a vertebrate

Class Trematoda: Ex. Chinese Liver Fluke Common in China, Korea Japan, where practice of eating uncooked fish is common Adults live in the liver and bile passages Clonorchis sinensis

Class Trematoda: A snail is usually the intermediate Host Schistosoma mansoni A snail is usually the intermediate Host

Class Trematoda: Eggs pass through blood vessel into gut, and out…. Or they lodge in nervous tissue, muscles, other organs, causing excrutiating pain &tissue damage. Schistosome life cycles are unusual in several ways -- One intermediate host -- Have Separate Sexes! -- Adults live within blood vessels, feed on blood Schistosome Egg and spine

Class Trematoda: Schistosome life cycles are unusual in several ways Separate sexes: dioecious Picture of the Happy couple

Of 200 million infected approximately 120 million show symptoms Of 200 million infected approximately 120 million show symptoms. The mortality rate is about 2.5% but more frequent in children (5 million deaths, 200K in Sub-Saharan Africa alone)

3 species mainly invade humans S. japonicum S. haematobium S. mansoni

General Pathology S. mansoni, S japonicum Acute schistosomiasis: fever, nausea, cough etc., and granuloma formation after female begins to lay eggs Chronic Schistosomiasis: could be years later intestinal schistosomiasis: granulomatous inflamation around eggs; colonic polyps, especially in Egypt. hepatosplenic schistosomiasis: inflammation around eggs trapped in liver, leading to fibrosis, cirrhosis S haematobium: parasites in the bladder and ureter, can lead to calcification, cancer….”urinary schistosomiasis”