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Phylum Nematoda = aka the roundworms Triploblastic Pseudocoelomates Unsegmented Marine, freshwater, parasitic Enormous economic relevance Environmental importance General Body Plan Few mm - massive (30 feet or 9m, parasite in whales) Anterior mouth followed by continuous digestive tract Cuticle with no external cilia Internal Structures - Noncellular, collagenous cuticle - May have spines, bristles, papillae, or warts - Maintains internal hydrostatic pressure - Mechanical protection - Resists digestion by the host - Longitudinal muscles are used for locomotion Microscopic Structure Dorsal nerve cord Muscle cells Epidermis Intestine Lateral nerve cord Excretory canal Cuticle Nerve cord Pseudocoel Body wall detail Nucleus Protoplasmic Extension of nerve cell Contractile muscle element Nerve cord Sensory structures Some with lips, some have spines or teeth on those lips Amphids –chemoreceptors along the cuticle Phasmids - chemoreceptors near the anus Ocelli – eyespots found in Amphid aquatic nematodes Papilla Feeding and digestion Complete digestive tract Regional specialization Pharynx = pump – Carnivores – Herbivores – Omnivores – Saprobes (decomposers) – Parasites Other Structures Lateral nerve cord Renettes – absorb nitrogenous waste = form canals in parasitic forms Excretory canal Reproduction Dioecious Sexual dimorphism – Males » One testis » Bursa – Females Male Female » Pair of convoluted ovaries » Oviducts become uterus » Several hundred to several hundredthousand eggs per day » Ovovivparity – giving birth to larvae that hatched from an egg Important Parasites Ascaris lumbricoides – “The Giant Intestinal” roundworm (35 cm) – 800 million infected – Live in small intestines of humans – Transmitted through feces contact – Once the eggs are ingested, they hatch and travel to the lungs – After two moltings, they travel to the trachea where they are swallowed • Enterobius vermicularis – Pinworm – Staple size (1-2mm) – Live in rectum – At night females migrate out of the anus and lay eggs on skin • Necator americanus – Hookworm – Penetrates skin, usually feet – Females may lay 10,000 eggs/day • Trichinella spiralis – Porkworm – Transmission through eating uncooked pork – Can cause loss of muscle control or death – Now, less than 12 cases per year • Wuchereria – Filarial worms – Infect the lymph vessels which are responsible for returning fluid to the circulatory system – Cause trichinosis or elephantiasis
