Phylum Nematoda Kingdom Animalia



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Phylum Nematoda

Kingdom Animalia

  • Animalia

  • Parazoa

  • Eumetazoa

  • Protostomia

  • Spiralia
  • Platyzoa – flatworms, rotifers
  • Trochozoa – mollusks, annelids
  • Ecdysozoa – nematodes, arthropods
  • Deuterostomia

  • Protostomes are divided into

  • Spiralia – flatworms, rotifers, molluscs, annelids

  • Ecdysozoa – animals that molt (nematodes, arthropods)

  • Ecdysozoa is a relatively recent group

  • Old story line in general biology was a gradual increase in complexity

  • Through series of three body plans

  • Segmentation (uniting annelids and arthropods)

  • Turned out to be a fractured fairy tale…

  • Many organisms appeared to be primitive but were not really (flatworms, nematodes)

  • Body plans did not necessarily correspond to clades, some secondarily primitive etc…

  • Segmentation turned out to be independently evolved in annelids and arthropods…

  • Ecdysozoa - ecdysis means periodically shedding an exoskeleton in order to grow

  • Cuticle molted

  • Radial cleavage

  • Don’t use cilia to move

  • Lack trochophore larva (found in molluscs and annelids)

  • Over 12,000 sp., maybe over 1 million!!, from Gr. nema = thread

  • Potentially the most diverse group next to arthropods (mostly undiscovered)

  • Incredibly abundant - 1 million worms per shovel full of garden soil, over 1 billion per acre of farmland

  • Most are tiny (~ 1 mm), but Ascaris can reach 50 cm. (~ 20 inches)

  • Round, bilaterally symmetric

  • Pseudocoelomate (most pseudocoels are ecdysozoans)

  • Mainly aquatic

  • Usually molt four times during their lives

  • Carnivores and parasites

  • Lack circular muscles, use longitudinal muscles so thrash wildly about

  • Interstitial habitat important (on land and in the sea) - life between the grains of soil…

  • Because grains of soil are often covered with thin film of water, even terrestrial worms are basically aquatic

  • Tough cuticle (non-living outer layer) resists abrasion, rings provide grip on surfaces to help burrow

  • Unlike arthropods, cuticle has no chitin, uses collagen

  • So nematode cuticle is porous, can still rely on diffusion


  • Streamlined roundworm shape is an adaptation for moving through the soil

  • Thrashing motion due to lack of circular muscles is a great adaptation for wriggling between grains of sand

  • Excrete ammonia by diffusion

  • Exchange gases by diffusion

  • Primitive nervous system - nerve ring for brain, dorsal and ventral nerve cords

  • Bristles and other structures for primitive mechanical and chemical senses

  • Most have separate sexes

  • Sexually dimorphic, males are smaller

  • Males have a copulatory hook to hold open the female’s genital pore

  • Many harmful parasitic species:

  • Ascaris etc. - intestinal roundworms, common in young vertebrates - close to the soil

  • Infects 1 of 6 people worldwide, especially common in children in the southeastern US

  • Female worm can hold up to 1 million eggs, and can lay up to 200,000 eggs per day!!


  • Many harmful parasitic species:

  • 340 million Ascaris victims per year with serious side effects, 100,000 deaths per year!

  • Filarial worms - infect lymph system, cause grotesque swelling = elephantiasis

  • Many harmful parasitic species:

  • Trichinella - causes trichinosis in vertebrates (birds and mammals), worms form cysts in muscles of pigs etc

  • Up to 500 million worms tunnel through host’s body - permanent organ and muscle damage

  • Many harmful parasitic species:

  • Hookworms - common in school children

  • ~ 570 to 740 million people infected in the tropics alone - worms leave in feces, reenter through the soles of the feet

  • At its peak in the late 19th and early 20th Century, hookworm infected ~ 40% of all southerners

  • Primarily a disease of poor rural areas

  • Enters through the soles of the feet, especially the skin between the toes

  • Once in the body, hookworm migrates through the blood to the lungs, up into the throat

  • Swallowed, carried down to the small intestine where it attaches itself to the lining of the intestine

  • Feeds on the hosts blood

  • Female lays up to 10,000 eggs a day, deposits them directly in the intestine

  • Eggs are shed in feces

  • If feces are deposited on warm soil, eggs hatch into larvae

  • Can live in the soil for months before a victim comes along

  • Southern soils and climate provided a nearly perfect new home for this old world parasite

  • Primitive sanitary conditions in the south were a perfect breeding ground

  • Bare feet (poverty), little medical care, no public health programs

  • African Americans proved more resistant, maybe due to long exposure in native Africa

  • Slaves were healthier than the overseers!

  • Subtle evolutionary revenge on slave owners!

  • Symptoms are many and varied…

  • Victims become pale, anemic, severe digestive problems

  • Infection dulls mental processes, victims are easily fatigued - hence “germ of laziness”

  • Muscles become weak, so abdomen protrudes (potbelly)

  • Victims have a gaunt appearance, protruding shoulders (angel wings)

  • Get unusual dietary cravings (pica) - eat chalk, dirt, paper..

  • Some were so badly infected they were blind, fluid of the eyes was filled with live worms!!

  • Widespread infection and suffering, went unrecognized until the early 20th Century

  • Charles Wardell Stiles, zoologist with the USDA, was responsible for uncovering the extent of the infection

  • Got John D. Rockefeller to fund a massive study, treatment program

  • Poor condition of southern soldiers may have contributed to the outcome of the Civil War

  • Robert Penn Warren describes rebel soldiers as “those gaunt, barefoot, whiskery scarecrows”

  • Popular image of southerners as lazy, shiftless, dull-witted, etc…

  • All symptoms of the germ of laziness

  • Rockefeller Sanitary Commission for the Eradication of Hookworm Disease (1910-1915)

  • Stiles found it very difficult to eradicate

  • Subject of privys and excrement were taboo, especially in mixed company

  • Stiles was sometimes threatened with violence when trying to interview victims, or asking for stool samples

  • Editors of the Rockefeller Commission reports asked him to remove the section on privys as “exceedingly undignified, even disgusting”

  • Mistrusted by medical doctors because he was a zoologist

  • Mistrusted by local public health officials and residents as a carpetbagger

  • Southerners took great offense

  • “Where was the hookworm or lazy disease when it took five Yankee soldiers to whip one southerner?” asked the Macon Telegraph

  • Many thought the whole thing was a conspiracy to sell shoes while Rockefeller secretly bought up shoe factories!

  • Indoor plumbing essentially nonexistent, even outhouses few and far between

  • 80% of southern rural schools and churches lacked a privy

  • Even fewer found in rural farms and homes

  • Despite massive attempt to train public health officials, local doctors, school children, mistrust undermined all efforts

  • Tulane Medical School was one of the few supporters, exemplary in training its doctors to diagnose and cure the infection


  • New vaccine enters clinical trials in Africa in 2014

  • Goes after two key enzymes in hookworm metabolism, slowly kills it

  • Ecological importance

  • Aerate the soil (like earthworms)

  • Recycle bacteria and fungi into animal tissue

  • Guinea worm (Dracunculiasis medinensis) is thought to be the fiery serpent of biblical Israelites

  • Probably dates to Ancient Egypt (Pharaoh worm)

  • Mentioned also in the Sanskrit Rig-Veda (14th Century BC)

  • Arabs, Persians, were familiar with it, called it Medina vein – described by Rhazes and Avicenna in the 9th Century AD

  • Adult nematode worm up to 1200 mm long!

  • Intermediate host is a type of aquatic invertebrate called a copepod

  • Copepod intermediate host discovered in 1870 by Alesej Pavlovich Fedchenko, a major step in early tropical medicine

  • Worm enters the body through drinking water supply via the copepod

  • Copepod dissolves in the stomach, releasing larval worms

  • Worm matures and begins to tunnel under the skin

  • Secretes irritant that causes papules to form on ankles and wrists

  • Drives people to water, eggs released in water, eaten by copepod, people consume copepods when drinking water

  • Ancient remedy was to patiently wind the worm out on a stick!!

  • Practice was so common, physicians advertised with signs showing a worm on a stick

  • This remedy is depicted on the staff of the Greek physician Asclepius

  • Thought to have practiced around 1200 BC, immortalized in the Iliad, revered as the Greek god of medicine

  • This staff of Asclepius is the true symbol of the medical profession

  • The caduceus (entwined snakes) is really the symbol of the herald (Mercury) !?!

  • Why did doctors switch to the caduceus of Mercury?

  • Medicine was traditionally associated with alchemy, and alchemists were associated with Mercury (the hermetic arts)!



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