Download Phylum Nematoda

Phylum Nematoda
Learning outcomes
• Describe structure and
characteristics of nematodes
• Nematodes resembles a tiny thread
• Greek word “nema” means "thread’’
Nematode Diversity
• 28,000 species described
• 5 million awaits description
• Found in almost everywhere
• Abundant in marine, freshwater, and soil habitats.
“They are the most numerous multicellular animals
on Earth".
• One square meter of top soil may contain several
million nematodes.
• Most are free-living, some are parasitic
Nematode body - long
- narrow
- cylindrical
- tapers at both ends
Most are microscopic - average size 1 mm – 5
mm but extend to 1 m
They are unsegmented worms
Also refer as
“Roundworms”
Characteristics of
Phylum Nematoda
• Bilateral symmetry
• Triploblastic
• Nematodes have a pseudocoelom (tube-withina-tube).
• Pseudocoelom is a closed fluid-filled space that
acts as a hydrostatic skeleton.
• - It helps in circulation and dispersal of
nutrients.
• Nematodes have a complete digestive system.
It is tubular.
- Pharynx is muscular
Lumen of the pharynx is tri-radial
Excretory system:
- two lateral longitudinal tubes
Nervous system:
An anterior nerve ring (brain), a ventral
and a dorsal nerve cord
Nematodes do not have a circulatory and
a respiratory system.
Reproductive system
Male and Female animals are separated
Body cover :
The epidermis is a single cell layered. It is a
syncytium.
Epidermis secretes a thick collagenous cuticle
(non cellular- multi layered).
Cuticle –
- serves as an outer skeleton (Body support)
- flexibility helps body movement
- permeable to water and gas
Cuticle is periodically shed as it grows.
( four times before reaching the adult stage)
Nematodes do not have circular muscle layer. They can only
bend its body from side to side, cannot crawl.
Free-living Nematodes
Feed on algae, fungi, small animals, dead
organisms and living tissues.
Caenorhabditis elegans, which lives in the soil is a
model organism.
Free-living nematodes
- serve as bio-indicators
- decomposition of organic material and the
recycling of nutrients in soil.
Insect Parasitic Nematodes
They are Beneficial use as biological control of
insect pests
Nematodes become harmful;
- parasitize man and other animals
(Animal parasitic)
- damage our crops (Plant parasitic)
Enterobius vermicularis – Pinworm
Adult nematodes live in the large intestine
•White colour
•Females with pointed posterior
Female lays eggs around the
edges of the anus
Ascaris lumbricoides - Adult nematodes live in the intestine.
A female may produce 100,000 eggs which are passed with
the feces.
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Hookworms
Ancylostoma duodenalae
Necator americanus
Wuchereria bancrofti - filarial nematode
(long and thin worms)
lymphatic filariasis, elephantiasis.
Trichinella spiralis - Trichinosis in humans
Trichinella
Cyst
in pork cyst
• Plant parasitic nematodes damage to crops
• Soil is an excellent habitat for plant parasitic
nematodes