Platyhelminthes: Flatworms

Phylum Platyhelminthes Phylum Platyhelminthes - Flatworms Soft, unsegmented, flattened worms that have tissues and internal organ systems Have three embryonic germ layers Simplest animals with bilateral symmetry Exhibit cephalization More developed organ systems than Poriferans and Cnidarians Acoelomates – “without a coelom” – a coelom is a fluid-filled body cavity that is lined with mesoderm

Anatomy of a Flatworm Freshwater flatworms have simple ganglia and nerve cords that run the length of the body. The excretory system consists of a network of tubules connected to flame cells that remove excess water and cell wastes. Most flatworms are hermaphrodites, having male reproductive organs (testes) and female reproductive organs (ovaries) in the same organism. Flatworms use a pharynx to suck food into the gastrovascular cavity. Digested food diffuses from the cavity into other cells of the body. Eyespots in some species detect light. Eyespot Head Gastrovascular cavity Ganglia Nerve cords Excretory system Mouth Pharynx Ovary Testes Excretory tubule Flame cell

Feeding in Flatworms Can be carnivores or scavengers Gastrovascular cavity with one opening at the end of a pharynx Digested food diffuses to other body tissues

Respiration, Circulation, and Excretion in Flatworms No circulatory system or respiratory organs – rely on diffusion to transport nutrients and waste Expel undigested material through pharynx Flame cells filter and remove excess water and wastes from body

Response in Flatworms Nervous system much more developed than Sponges or Cnidarians Definite head Simple ganglia control nervous system Two nerve cords run from ganglia along both sides of body Ocelli, or eyespot, detects changes in the amount of light in their environment

Movement in Flatworms Cilia on epidermal cells Muscle cells allow to twist and turn to be able to react rapidly

Reproduction in Flatworms Sexual – hermaphrodites – two worms join as a pair and deliver sperm to each other Asexual – fission – splits in two

Penis Fencing in Flatworms

Groups of Flatworms 3 major classes of flatworms –C–Class Turbellaria –C–Class Trematoda –C–Class Cestoda

Class Turbellaria Free-living flatworms found in marine or freshwater Bottom dwellers Planarians – 1/2 cm to 6 m long

Examples of Class Turbellaria

Parasitic Flatworms Feed on blood, tissue, or cells; some just absorb nutrients through their “skin” Examples: Tapeworms, Flukes Very complicated sexual reproductive life cycles

Class Trematoda – Flukes Parasitic and infect internal organs of host Blood flukes Schistosoma mansoni Humans – primary host – burrow through exposed skin Many more eggs than free-living flatworms Eggs pass out with feces of host Tropical areas – Southeast Asia, Africa

Examples of Class Trematoda

Class Cestoda – Tapeworms Long, flat parasitic worms Head of an adult called a scolex – used to attach to intestinal wall where it absorbs nutrients 18m long, host may lose weight and become weak Behind scolex is a narrow neck region that produces proglottids that break off the tail and rupture in intestine or feces and release embryos Eggs consumed by intermediate host Larvae form cysts in muscle tissue Tissue then consumed by humans

Life Cycle of Tapeworm

Examples of Class Cestoda

Nematoda: Roundworms

Phylum Nematoda Phylum Nematoda - Roundworms Slender, unsegmented worms Pseudocoelom – body cavity only partially lined with mesoderm Two openings, mouth and anus, in digestive system – “tube-within-a-tube” – food moves only in ONE direction Microscopic in size to 1m long Can be decomposers or dangerous parasites Might be the most common multicellular animal Most are free-living, found everywhere

Feeding in Roundworms Mainly carnivores, some eat algae or decaying organic matter

Respiration, Circulation, and Excretion in Roundworms Exchange gases and excrete metabolic wastes through diffusion No internal transport system

Response in Roundworms Simple nerve network, ganglia

Movement in Roundworms Muscles and fluid = hydrostatic skeleton

Reproduction in Roundworms Sexual – internal fertilization Ascarid worms – complex life cycles involving two or three different hosts or several organs within a single host Stomach – lung – throat – intestine - feces

Examples of Nematodes

Roundworms and Human Disease Hookworms – similar to Ascaris lifecycle, except they enter through the skin Filarial Worms – elephantiasis (swelling of body) – transmitted by mosquitoes ORGANISM Trichinella Filiarial worms Ascaris Hookworms ORGANISM Trichinella Filiarial worms Ascaris Hookworms DISEASE Trichinosis Elephantiasis Ascaris infection/ infestation Hookworm infection/ infestation DISEASE Trichinosis Elephantiasis Ascaris infection/ infestation Hookworm infection/ infestation ROUTE OF INFECTION Eating undercooked meat containing larval cysts Bite of insect carrying filarial worms Eating unwashed food contaminated with Ascaris Bare skin in contact with contaminated soil ROUTE OF INFECTION Eating undercooked meat containing larval cysts Bite of insect carrying filarial worms Eating unwashed food contaminated with Ascaris Bare skin in contact with contaminated soil DESCRIPTION Larvae burrow into tissues of host, causing pain Worms block passage of fluids within lymph vessels, causing tissues to swell Worms in intestine block normal passage of food and absorption of nutrients Worms attach to intestinal wall and suck blood, causing weakness and poor growth DESCRIPTION Larvae burrow into tissues of host, causing pain Worms block passage of fluids within lymph vessels, causing tissues to swell Worms in intestine block normal passage of food and absorption of nutrients Worms attach to intestinal wall and suck blood, causing weakness and poor growth