Phylum Nematomorpha “Horsehair worms” in Jaycox Creek In parasitology, the term paratenic describes a host that is not necessary for the development of a particular species of parasite, but nonetheless may happen to serve to maintain the life cycle of that parasite.

Phylum Nematoda (round worms) 20 K species described but plenty more unknown Occur in every conceivable habitat on Earth Probably most abundant animal group ( 1 million/m2 in sediments) Important parasites of plants and animals 1 mm

Gut complete and differentiated

Phylum Nematoda (round worms) General Characteristics Pseudocoelomate or acoelomate Unsegmented Organs not enveloped in peritoneum No circular muscles or cilia

Gut complete and differentiated Inflexible cuticle and tight musculature maintain a very high hydrostatic pressure in the body cavity. What keeps the stomach from collapsing? Pharynx keeps pumping fluid to keep the stomach turgid. Nematodes feed on cell sized particles (e.g. bacteria)

Other Common name: Whipworms Arrangement of muscles and functioning of the nervous system imposes limitations on locomotory movement. Nerve cords do not innervate muscles; rather non-contractile extensions of the muscle fibers hook up to the nerve cords Other Common name: Whipworms

Nematoda Phylogeny recent analyses of morphology and gene sequences suggests they are related to the arthropods ecdysone-like molting hormones in some nematodes and insect molting hormone stimulates at least one nematode species to molt. Grouped with arthropods and several other small phyla into a clade or lineage called the Ecdysozoa

Nematodes are very important as: Plant parasites Biological pest control for crops Parasites of vertebrates: hookworms pinworms heartworms trichina worms filarial worms Biological Models

Hookworms and pinworms drink blood, infections of 1000 worms per host are not unusual… half a liter of blood Wucheraria plugs the lymphatic system causing substantial buildup of fluid and subsequent dense growth of connective tissue ; 120 million people are afflicted presently Many make extensive migrations; Larvae of Onchocerca often migrate to the victim’s eyes. Chronic damage is responsible for River blindness…18 million Pinworms infect about 500 million people, 20% of U.S. children Dracunculus medinensis, the female, often 1 m long, releases ulcer producing secretion. When the skin comes into contact with water she lays millions of offspring in a day. Juves are ingested by copepods, and pass to humans who drink contaminated water

Is trichinellosis common in the United States? Infection used to be more common and was usually caused by ingestion of undercooked pork. However, infection is now relatively rare. During 2008–2010, 20 cases were reported per year on average. The number of cases decreased beginning in the mid-20th century because of legislation prohibiting the feeding of raw-meat garbage to hogs, commercial and home freezing of pork, and the public awareness of the danger of eating raw or undercooked pork products. Cases are less commonly associated with pork products and more often associated with eating raw or undercooked wild game meats. Several safe and effective prescription drugs are available to treat trichinellosis. Treatment should begin as soon as possible and the decision to treat is based upon symptoms, exposure to raw or undercooked meat, and laboratory test results. Nausea, diarrhea, vomiting, fatigue, fever, and abdominal discomfort are often the first symptoms of trichinellosis. Headaches, fevers, chills, cough, swelling of the face and eyes, aching joints and muscle pains, itchy skin, diarrhea, or constipation may follow the first symptoms. If the infection is heavy, patients may experience difficulty coordinating movements, and have heart and breathing problems. In severe cases, death can occur.

Biological Models: Caenorhabiditis elegans grown in small petri dishes, fed bacteria, parthenogenic Small cell # (hundreds), 6 chromosomes, 20,000 genes, first animal whose genome was sequenced, - Eutely: limit # of cells as adult; growth by cells becoming larger Apoptosis: extensive programmed cell death -Chromosome diminution: During embryogenesis, the elimination of certain chromosomes from cells that form somatic tissues- a very unusual mechanism of gene regulation. C. elegans cell line showing extensive apoptosis