Unsegmented Worms: Flatworms and Roundworms Biology 11

Worms Divided into 2 Groups Unsegmented Segmented Flatworms Roundworms Annelids

Phylum Platyhelminthes Platy= flat Helminth=worm The Flatworms

Characteristics Acoelomates (no fluid filled space) Unsegmented body (not divided into sections) Live in aquatic habitat (streams, lake, oceans) Free living or parasitic Cephalization- concentration of sensory organs at one end Bilaterally symmetrical

Germ Layer 3 cell layers- ectoderm, mesoderm, endoderm Have a two way digestive system (lack an anus)

Class Tubellaria Free living flatworms Marine and fresh water (a few terrestrial) Reproduce asexually by fission and sexually are hermaphrodites

Class trematoda Parasitic flukes Live as external and internal parasites on fish and other animals Complex parasitic life cycle involving hosts Hermaphrodites

Class Cestoda Parasitic tape worms Live in intestines of vertebrates Have scolex in “head” section that have sections called proglottids Contain reproductive organs and fertilization takes place inside Mature proglottids detach and pass out of the intestine

Phylum Nematoda The roundworms Found in soil, marine, and fresh water

Cylindrically shaped Bilaterally symmetrical 3 body layers- have pseudocoelom

One way digestive system No circulatory or respiratory system Have mouth and anus No circulatory or respiratory system Fluid in pseudocoelom distributes food and oxygen Have nerve ring around pharynx (no brain) Have separate sexes

E X T R E M E H E E B Y – J E E B I E S A H E A D !

Loa loa is a blood dwelling nematode that is parasitic in humans Loa loa is a blood dwelling nematode that is parasitic in humans. The adult worm wanders through the subcutaneous tissue but is most obvious as it crosses the conjunctiva of the eye hence leading to its common name, the African eye worm. Like all roundworms, Loa loa is sexual so a male and female worm must be present in the same host for a full infection to ensue. Upon reproduction the female worm produces sheathed eggs called microfilariae which circulate in the blood stream.

Roundworms found in dog poop

Dog Heartworm

Inside a chicken’s intestine

Feeding Most are free living carnivores/omnivores Have pharynx Can be parasites in plants and animals

Respiration and Circulation Diffusion of gases through body walls

Excretion Metabolic wastes diffuse through body walls Undigested wastes through anus

Guinea Stickworm Guinea worms (dracunculiasis) result when a person swallows a small crustacean (cyclopoid) that contains the parasite. The juvenile parasite is released in the gut.  This parasite migrates to a position just under the skin, usually in the armpit or junction of the leg to the body. Males die shortly after mating.  The females then migrate to the skin of the arms or legs and cause a blister which contains juvenile parasites. The blister ruptures, and the young worms exit. Cold water is a trigger that causes the female to release the juveniles.  In the normal cycle, these juveniles are eaten by the crustacean that is then ingested by the human host. The historical treatment for guinea worms is to pull them out slowly, centimeter by centimeter, by winding them on a stick.  Cold water triggers the female worm to expel enough juveniles to allow about 5 cm of her body to be pulled out.  This procedure is repeated once a day.  Complete removal of the worm takes about 3 weeks. Guinea worms can also be removed by surgery or eradicated through drug therapy.  Metronidazole is the drug of choice, but thiabendazole or mebendazole can also be used. a nematode which we catch by drinking contaminated water. The females grow to a metre long - starting in the abdominal cavity and down an extremity, and stick their heads out through ulcers. The only way to remove these is to slowly wind them onto a stick (half a turn per day). The name refers to the Firey Serpent and that pretty much explains how it feels. Thought to be a possible origin for the caduceus (winding a serpent onto a stick). The Guinea worm starts off its life cycle living inside a microscopic copepod that swims around in fresh water. When a person drinks the water, the stomach acid dissolves away the copepod. But the larva manages to survive and burrows its way out of the intestinal wall. It wanders around the abdominal cavity looking for a mate. The male Guinea worms get up to 2 inches long. The females can get up to 2 feet long. When they mate, the male dies. The female starts traveling through the connective tissue of a person's body, down into their leg. All the while, its fertilized eggs are developing. It crawls to the leg and starts releasing the larvae just under the skin. That creates a very painful blister that people generally want to wash off in water. Which is exactly what the parasite wants the person to do! The blister pops and the larvae go into the water. When the Guinea worm senses the water being poured on it, it will slowly start pushing itself out of a person's body and releasing more larvae. Once in the water, they go off looking for another copepod. Assure me there's a cure. There's no drug you can take if you get Guinea worms. The only "cure" is one that's been around for thousands of years. As the Guinea worm is pushing itself out of your body, you slowly wrap it around on a stick. You don't want to grab it and pull it out because it will break and die, and then you have a 2-foot-long parasite in your body that will cause infection and might very well kill you.

Female anterior and posterior end

Filarial worms Tropical Asia Mosquito carries worms from host to host Cause elephantiasis