1. Nematodes, or roundworms, are a diverse phylum of small, unsegmented worms found in nearly every ecosystem. They include both free-living and parasitic species. 2. Four other phyla - Nematomorpha, Priapulida, Kinorhyncha, and Loricifera - are also discussed as they are considered close relatives of nematodes. 3. Important nematode model organisms like Caenorhabditis elegans are discussed in terms of their roles in research related to neuroscience, aging, and cryobiology.

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Image Credit1
Jackson David Reynolds
University of North Georgia
PHYLUM NEMATODA
AND FOUR PHYLA OF LIKELY NEMATODE RELATIVES

2. PHYLUM NEMATODA
the roundworms
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Image Credit11

3. 3
nematos
(G: thread)
nem-ah'-tō-dah
Reference2

4. – Nathan Augustus Cobb, PhD, 'Father of Nematology'
"In short, if all the matter in the universe except the nematodes were
swept away, our world would still be dimly recognizable, and if, as
disembodied spirits, we could then investigate it, we should find its
mountains, hills, vales, rivers, lakes, and oceans represented by a film of
nematodes.The location of towns would be decipherable, since for every
massing of human beings there would be a corresponding massing of
certain nematodes.Trees would still stand in ghostly rows representing our
streets and highways.The location of the various plants and animals would
still be decipherable, and, had we sufficient knowledge, in many cases even
their species could be determined by an examination of their erstwhile
nematode parasites."
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Reference5

5. "ROUNDWORM" BASICS
• "Roundworms"
• Unsegmented
• Acoelomate/pseudocoelomate
• Cuticle (chitinous)
• Most gonochoristic; some parthenogenetic
• Males & hermaphrodites
• Chromosome diminution
• Very ubiquitous
• >25K species currently described
• Free-living & parasitic species
• Eutelic*
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5
Reference2,7

6. NEMATODE ANATOMY
Image Credit8
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7. MUSCULATURE, INTERNAL PRESSURE,
& LOCOMOTION
• Rigid cuticle; musculature always partially contracted
• Very high hydrostatic pressure (p) within the
pseudocoel of 70-100 mmHg {pNML in most
annelids is 1-10 mmHg}
• Lack circular muscles
• No peristaltic waves
• Sinusoidal locomotion
• Myocyte extensions project to a nerve cord,
not vice-versa
• Muscular pharyngeal activity keeps gut held open
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Image Credit2

8. EUTELIC
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(with an asterisk)
"Here we show that many,
perhaps most, nematode
species are not eutelic in at
least one organ, the
epidermis, and that in this
respect they resemble other
model organisms such as
fruitflies and mice."*
– Cunha, et al., 1999
* Bold, italics, and underlining added. Reference7

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10. PARASITIC NEMATODES
• Parasitize vertebrate & invertebrate hosts, as
well as plants
• "Hookworms"
• Elephantiasis – filiarial nematodes w/
arthropod intermediate host
• Complex life cycles with extreme fecundity
(up to 1.5 x107 offspring/day!)
Image Credit21
Reference2
Image Credit22
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11. BENEFICIAL NEMATODES
• Most nematodes are free-living & non-parasitic
• Nutrient cycling in soil
• Food sources for commercially important animals
• Used to control insect pests in gardens
• Research (specifically w/Caenorhabditis elegans)
• Neural network modeling
• Senescence research
• Cryonics/cryobiology
Reference2,23,24
Image Credit25
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12. CAENORHABDITIS ELEGANS
• Neural network mapping/engineering
• OpenWorm (www.openworm.org)
• Strategies for Engineered Negligible
Senescence (SENS) Research Foundation
• Calorie restriction in C. Elegans
• Aubrey De Grey, PhD
• Cryonics
• ALCOR Life Extension Foundation
Image Credit26Reference26,27,28,29,30,31 Image Credit32
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13. FOUR PHYLA OF LIKELY
NEMATODE RELATIVES
Nematomorpha, Priapulida, Kinorhyncha, & Loricifera
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14. PHYLUM NEMATOMORPHA
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(G. thread form)
Image Credit12Reference10

15. "HORSEHAIR WORM" BASICS
• "Horsehair worms"
• Parasitic
• Pseudocoelomate
• Lack functional digestive tract (as adults)
• Gonochoristic; internal fertilization
• Exhibit no eutely in any tissues
• Molting
• Life cycle not yet entirely understood
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Reference2
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(G. the penis)
Image Credit13
PHYLUM PRIAPULIDA
Reference9

17. "PENIS WORM" BASICS
• "Penis worms"
• Body cavity extensive – contains amoebocytes
& erythrocytes
• All free-living & marine – in muddy sediments
• Secrete & periodically molt chitinous external
cuticle
• Circular body cross-section – w/o septa
• Gonochoristic
Reference2Image Credit20
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18. PHYLUM KINORHYNCHA
{ECHINODERIDA}
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(G. movable snout; G. hedgehog hide)
Image Credit14Reference9

19. "MUD DRAGON" BASICS
• "Mud worms/mud dragons"
• Body consists of 13 segments
• Bona fide pseudocoelomate
• Body usually >1 mm in length
• All marine
• Crawl through sediment w/use of recurved
spines on eversible head
Reference2 Image Credit19
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20. PHYLUM LORICIFERA
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(L. armor bearing)
Image Credit15Reference9

21. LORICIFERAN BASICS
• Phylum created in 1983
• 50-500 µm in length
• O2-devoid sediments
• 6 overlapping segments
(lorica – "armor") on posterior half of
body – chitinous; individually operated
by underlying musculature
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Image Credit16

22. A EUMETAZOAN
WITHOUT MITOCHONDRIA
• Hydrogenosome-like
structures anaerobically
synthesize ATP
• Anabolic process similar to
that in some anaerobic
fungi/ciliate protozoa
• Only known eumetazoans
to date devoid of
mitochondria
Reference2,17Reference17
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