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Aschelminthes: Roundworms Not the Phylum name 7 Phyla in this grouping Characteristics • • • • • • • Most are freshwater Cylindrical Unsegmented Bilaterally symmetrical Triploblastic (pseudocoelomates) Dioecious Thin, tough external cuticle Characteristics • Pseudocoelom – 1st distinct body cavity – Internal organs lie free in the cavity – Serves as a cavity for digestion, circulation and helps with locomotion Characteristics • Digestion – Two body openings – Mechanical breakdown of food, digestion, absorption, feces formation • Gas Exchange and Nitrogenous wastes are diffused across the surface of the animal. Phylum Rotifera • “wheel bearer” • ~2000 species • Characteristic ciliated organ: corona – Provides locomotion and food gathering (small microorganisms) • • • • Free-living Primarily freshwater (<10% marine) Pharynx contains mastax (jaws) Some reproduce through parthenogenesis Phylum Kinorhyncha • • • • • “kinorinks”, “motion snout” ~150 species, <1 mm long Burrow into the mud/sand with snout Only found in marine environments 13-14 zonites (spines/plates) – Young will grow and molt to get all zonites • Complete digestive system Phylum Nematomorpha • • • • ~250 species “horsehair worms” Adults are free-living Juveniles are parasitic – Arthropods (host) • Beetle and cockroaches – Found in Running/Standing Water Phylum Acanthocephala • “Spiny-headed worm”, “Thorny-headed worm • ~1000 species • Endoparasites (2 hosts required) – Juveniles: Parasites of crustaceans or insects – Adults: Parasites of mammals, birds, fish (attaches to intestinal wall) • Absorbs food directly through tegument Phylum Loricifera • Most recently discovered (1983) • Live in spaces between marine gravel • Spiny or brush head • Separate sexes • ~14 species Phylum Priapulida • ~16 species • Marine worms (found in cold waters) • Live buried in the mud/sand on the sea floor • Feed on small annelids and invertebrates • Separate sexes • ~2 mm to 8 cm Phylum Nematoda • “True Roundworms” • Some of the most abundant animals on Earth. ~16,000 species • One shovel of soil contains over 1 million nematodes (5 billion/acre) • Mostly parasitic (plants/animals) • Can be free-living in marine, freshwater or terrestrial environments Phylum Nematoda: Characteristics • Covered with tough cuticle – Provides protection and resists digestion by host • Unsegmented and tapered at both ends • Absence of circular muscles, prevents them from crawling…so they thrash about for movement • Excrete liquids through pore (tubular or glandular system) • Most are dioecious (females usually larger) – Ex: Guinea worm: males (1”), females (2-4’) • Juveniles will molt into adult body form. Phylum Nematoda: Ascaris Roundworm • Giant intestinal roundworm • Largest nematode (can grow over 1 ft) • Doesn’t cause serious health problems (may cause intestinal blockage) Phylum Nematoda: Ascaris Roundworm • Life cycle: – Human eats veggies grown in infested soil (eggs) – Eggs hatch in intestines, bore a hole through the intestinal wall. – The larvae will enter the blood stream and make their way to the lungs. – Larvae is coughed up the trachea and swallowed back down the esophogus – Ascaris roundworm will mature into adults and reproduce in the intestines. – Fertilized eggs leave the host (w/feces). Eggs are protected by tough shells and can survive in the environment for up to 5 years. Phylum Nematoda: Hookworm • Life cycle: • Attaches to intestine and sucks blood- can cause much damage as host often loses blood (anemia) • Serious problem in warm, moist areas where people walk barefoot • Larvae develop in soil and enter host through cracks in foot • Life cycle like Ascaris Phylum Nematoda: Trichinella spiralis (The porkworm) • Life cycle: – Adult worms live in the small intestines of humans (or other carnivores/omnivores). – Adult females give birth to larvae, which enter into the circulatory system and are carried to muscle tissue. – Larvae encyst in host’s muscle tissue (remain here for many years). – Another host must ingest infective muscle tissue to continue the life cycle. – Once ingested, the larvae excyst in their stomach and make their way to the small intestine (molt 4 times) and become adults. 1 gram of pork can contain 3000 cysts! Phylum Nematoda: Human Pinworm • Most common roundworm parasite in the United States • Life cycle: – Adult pinworms live in the lower region of the large intestines – At night, gravid females move to the rectum and deposit eggs (and then die). – The females and eggs produce an itching sensation. – When the host scratches the itch, the hands and bedding become contaminated with the eggs. – Hands touch the mouth, eggs are swallowed and then hatch. – Larvae molt four times in the small intestine and migrate to the large intestine. Phylum Nematoda: Filarial Worm • Life cycle: – Live in the lymphatic system and block vessels – Fluid and connective tissue accumulate in these blocked vessels and cause enlargement of various appendages (called elephantiasis) – The adults reproduce in the lymphatic vessels and the larva are released into the blood stream. – Mosquitos feed on humans, ingests the larvae (the larvae molts twice) and then the larvae becomes infective. – Mosquitos feed on other human hosts and transfer the larvae. – The larvae molt two more times as they make their way to the lymphatic vessels. Phylum Nematoda: Filarial Worm • Filarial worms are very difficult to eliminate from the lymphatic system. • The goal is to destroy as many larvae as possible so that more individuals are not infected. • Heartworm is a filarial worm that affects dogs…prevention is key! Phylum Nematoda: Guinea Worm • Adult female can carry 3 million embryos • Life cycle: – Parasite will migrate just below the surface of the skin and eventually emerge (most cases in the feet) – Very painful blister forms (along with fever, nausea and vomiting). – Individuals try to soothe burning sensation by putting feet in water, which causes the female to expel thousands of eggs into the water. – Larvae can live in freshwater for a few days before finding a water flea (14 days) – People drink water (along with water flea), flea is digested releasing the larvae. – Male and female will reproduce a few months later (male dies), female spends the next year making her way to the foot. Phylum Nematoda: Ascaris Roundworm • Life cycle: