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Phylum Nematomorpha “ Horsehair worms ” in Jaycox Creek

Phylum Nematomorpha “ Horsehair worms ” in Jaycox Creek. 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/m 2 in sediments)

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Phylum Nematomorpha “ Horsehair worms ” in Jaycox Creek

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  1. Phylum Nematomorpha “Horsehair worms” in Jaycox Creek

  2. 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

  3. Gut complete and differentiated

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

  5. 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)

  6. 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

  7. 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

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

  9. 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

  10. Biological Models: Caenorhabiditiselegans • 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

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