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:

Loa loa worm