Download Phylum Nematoda - Sardis Secondary

Phylum
Nematoda
Biology 11
Invertebrates
Round Worms
 Microscopic to almost a meter long
 20,000 species; exist in every
ecological niche; marine,
freshwater, terrestrial, parasitic
 Bilateral symmetry
 3 cell layers
(endoderm, ectoderm, mesoderm)
 Pseudocoelom
Digestive System
 One of the first animals to have a complete, one way
digestive system with two openings (mouth and anus)
 Mouth, pharynx, long intestine, anus
Movement
 Muscles run in strips down the length
of the body wall
 Pseudocoelom acts as a hydrostatic
skeleton
 Enables movement due to the pressure of
the fluid filled cavity acting against the
muscles
 Have a rigid cuticle

Able to shed cuticle as organism
grows

Known as molting (molt 4 times
before adult)
Reproduction
 Sexually only
 Either male or female
 Some hermaphroditic
 Fertilization occurs in female
 Development inside or outside the nematode
 Females release approximately 240,000 eggs per day
Nervous System
 Simple nervous system

Nerve ganglion in the head region (NOT a brain)

Ventral and dorsal nerve cord extend the length of the body

Nerves transmit sensory information and control movement
 Sense organs that detect chemicals given off by prey or hosts
Respiration and
Circulation
 No internal transport system
 Breathe and excrete through their body walls
 Depend on diffusion to carry nutrients and wastes
through their body
Habitat
 Parasitic or free-living
 Free-living species found in all
climates (soil, salt flats, aquatic
sediments, polar regions, tropics,
fresh water, oceans, hot springs)
 Parasitic species live within a host
 Found within plants and animals
Ascaris
 Adults live in the intestines
 Eggs leave in feces and eaten by
another host
 Eggs hatch in intestines of new host
 Larvae enter blood stream
 Enter into lungs
 Coughed up into the mouth
 Ingested into intestines where they
mature into adults
Ecological Role

Important decomposers in the soil



Break down and recycle decaying matter
Parasitic roundworms affect humans:

Directly: human parasites

Indirectly: destruction of agricultural crops
Ascaris, Hookworm(live in intestines, bore through the skin of feet),
Trichinosis(live in muscles, from eating undercooked pork), Elephantiasis,
Pinworm (itchy anus)