This document summarizes information about the phyla Nematoda, Nematomorpha, and Tardigrada. It describes their distinguishing characteristics, life cycles, and examples of representative species. The phyla are protostomes that shed their cuticle to grow. Nematoda are roundworms found worldwide that are often parasites. Nematomorpha are horsehair worms that live as parasites in insects. Tardigrada are water bears able to survive extreme conditions like drying out or deep freezing.

1. Nematoda, Nematomorpha,
Tardigrada

2. Ecdysozoa
Protostomes that must shed their cuticle in order to grow
- Like the Lophotrochozoa, ecdysozoans do not share a common body plan
- Some are pseudocoelomate
- Nematoda and Nematomorpha
- Some are acoelomate
- Some are eucoelomate
- Panarthropoda (contains Tardigrada and Arthropoda)

5. Phylum Nematoda
Diversity
- 25,000 named species
- Maybe 500,000 - possibly more
Distribution
- Polar to tropics
- Marine, freshwater, and terrestrial
“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."

6. Phylum Nematoda

7. Phylum Nematoda
Life Style
- Nematodes are parasites of most all plants and animals
- Medical, veterinary, and agricultural losses are billion annually
- Many are free-living and feed on
- Bacteria,
- Yeasts,
- Fungal hyphae,
- Algae
- Predatory species may feed on rotifers, tardigrades, small annelids, or other
nematodes

8. Phylum Nematoda
Caenorhabditis elegans
- Model for understanding
development, gene function, and
programmed cell death

9. Phylum Nematoda
Form and Function
- Distinguishing features
- Cylindrical shape
- Cuticle (collagen)
- Secreted by hypodermis
- Hypodermal cords
- Lack cilia and flagella
- Longitudinal body muscles only
- Four bands
- Hydrostatic skeleton
- Eutely

10. Phylum Nematoda
Form and Function
- Distinguishing features
- Cylindrical shape
- Cuticle (collagen)
- Secreted by hypodermis
(epidermis)
- Hypodermal cords
- Lack cilia and flagella
- Longitudinal body muscles only
- Four bands
- Hydrostatic skeleton
- Eutely

11. Phylum Nematoda
Form and Function
- Distinguishing features
- Cylindrical shape
- Cuticle (collagen)
- Secreted by hypodermis
(epidermis)
- Syncytial
- Hypodermal cords
- Lack cilia and flagella
- Longitudinal body muscles only
- Four bands
- Hydrostatic skeleton
- Eutely

12. Phylum Nematoda
Form and Function
- Distinguishing features
- Cylindrical shape
- Cuticle (collagen)
- Secreted by hypodermis
(epidermis)
- Syncytial
- Hypodermal cords
- Lack cilia and flagella
- Longitudinal body muscles only
- Four bands
- Hydrostatic skeleton
- Eutely

13. Phylum Nematoda
Form and Function
Alimentary canal
- Mouth
- Muscular pharynx
- Non-muscular intestine
- Uses pressure of pseudocoelom
- Short rectum
- Anus
- Feces expelled through body pressure

14. Phylum Nematoda
Form and Function
Circulation and Respiration
- No dedicated organ systems
- Diffusion used

15. Phylum Nematoda
Form and Function
Nervous System
- Ring of nervous tissue and ganglia around pharynx
- Dorsal and ventral nerve cords
- Sensory papillae near head and tail
- Amphids on either side of head
- Primary sense organ

16. Phylum Nematoda
Form and Function
Reproduction
- Most are dioecious
- Female larger than male
- Fertilization is internal
- Development is direct
- Cuticle shed after each larval stage

17. Phylum Nematoda
Representative nematodes
Ariscas lumbricoides
- Warm, humid regions of the globe
- 1+ billion humans may be infected
- 30cm in length
- 200,000 eggs per day
- Shed with feces
- Can live in ground for weeks
- Find new host through consumption of contaminated food

18. Phylum Nematoda
Representative nematodes
Ariscas lumbricoides

19. Phylum Nematoda
Representative nematodes
Necator americanus - hookworm

20. Phylum Nematoda
Representative nematodes
Parelaphostrongylus tenuis - moose brain
worm

22. Phylum Nematomorpha
Horsehair worms
Form and function
- Long and slender
- 0.5-3mm diameter; up to 1m in length
- Body wall is similar to nematodes
- Cuticle
- Hypodermis
- Longitudinal muscles

23. Phylum Nematomorpha
Horsehair worms
Form and function
- Long and slender
- 0.5-3mm diameter; up to 1m in length
- Body wall is similar to nematodes
- Cuticle
- Hypodermis
- Longitudinal muscles

24. Phylum Nematomorpha
Horsehair worms
Form and function
- Digestive system
- Vestigial
- Larval forms absorb all nutrients
from hosts
- Adults absorb nutrients from the
water

25. Phylum Nematomorpha
Horsehair worms
Form and function
- Circulatory, respiratory, and excretory systems are lacking
- Nervous system is more simple than in Nematoda

26. Phylum Nematomorpha
Horsehair worms
- Reproduction
- Dioecious
- Adults mate in water and shed fertilized eggs into water
- Life cycles poorly known
- Gordius
- Juvenile nematomorphans encyst on vegetation
- May also infect through drinking
- Consumed by arthropods
- Several months spent in hemocoel
- Drive host to water and emerge

27. Phylum Nematomorpha
Horsehair worms

30. Phylum Tardigrada
Water bears or moss piglets
General characteristics
- < 1mm in length
- Approx. 900 species
- Mostly terrestrial, but some live in
freshwater, and a few are marine
- Elongated, cylindrical body;
unsegmented

31. Phylum Tardigrada
Water bears or moss piglets
General characteristics
- Head poorly defined
- Four pairs of unjointed legs
- Claws present
- Cuticle present and molted

32. Phylum Tardigrada
Water bears or moss piglets
General characteristics
- Mouth as buccal tube with
associated pharynx
- Adapted for sucking
- Needle-like stylets present
- Pierce cells of plants/animals

33. Phylum Tardigrada
Water bears or moss piglets
General characteristics
- Most of body is hemocoel
- True coelom restricted to gonadal cavity
- No circulatory or respiratory system
- All gas exchange via diffusion

34. Phylum Tardigrada
Water bears or moss piglets
Reproduction
- Dioecious
- Some species males are unknown;
parthenogenesis
- Egg laying occurs when cuticle is
shed
- Direct development

35. Phylum Tardigrada
Water bears or moss piglets
Hard to kill
- Diapause (encystment) - internal physiological mechanism
- Cuticle shed, and then replaced by several layers of simpler cuticle
- Lack legs and such.
- Quiescence (cryptobiosis) - state or dormancy maintained by environmental
factors
- Metabolic activities are non-existent
- Form a tun
- Withdraw legs, and lose much body water

36. Phylum Tardigrada

37. Phylum Tardigrada
Water bears or moss piglets
Hard to kill
- Cryptobiosis - can survive
- Anhydrobiosis - desiccation resistance
- Cryobiosis - temperature resistance
- Survive for years at -18C, can even survive -196C for a time
- Survive up to 151C
- Anyoxybiosis - no oxygen
- Vacuum - can survive in space
- Radiation - Ion radiation that would kill us is shrugged off