Nematodes, or roundworms, are one of the most abundant phyla of animals. They have a cylindrical shape with a flexible cuticle and lack organs like cilia. Nematodes can be free-living in soil and water or parasitic in plants and animals. They are classified based on features of their sensory organs, excretory systems, and male tail structures. Common examples are the human parasites Ascaris and Trichinella.

1. Presented By:
Faderog, Mary Grace
Soriano, Hannah Shane
Ang, Mary Grace Joy

2.  Free-living species
Caenorhabditis elegans
▪ Excellent model organism to
study biological phenomena
 Parasitic species
Ascaris lumbricoides
▪ Responsible for the most
common intestinal worm
infection ascariasis

3. Pseudocoelomate
(pseudo=false),becau
se they do not have
a true coelom. This
means that they do
have the peritoneal
cavity ( or gut), but it
is not lined with
mesoderm.

4. • Head
– Radially symmetrical
• Many planes divide
organism into two
mirror image
• Body
– Bilaterally symmetrical
• Single plane divides
organism into two
mirror images

5.  Ganglial
• Cerebral ganglion (“brain”)
– Anterior neural ring with most
of the sensory nerve bodies
• Two main longitudinal ganglial
chords
– Dorsal
– Ventral

6. • Complete digestive tract with
specialized regions
– Anterior mouth
– Muscular and glandular pharynx
(esophagus)
– Long, straight midgut (intestine)
– Rectum
– Ventral anus
• Secretion of digestive enzymes by
phanyngeal glands
• Absorption of nutrients through
microvilli of midgut cells Excretory System

7. • canal along each side of
body regulates nutrients
and waste content
• excretes nitrogenous
waste in the form of
ammonia through body
Wall

8. • long muscles under the cuticle, aligned
longitudinally under the epidermis, side to-side movement only (no
crawling or lifting itself); free swimming looks like it
is thrashing about aimlessly
• muscles activated by two nerves, one
along ventral (belly) and one along
dorsal (back)

9. • the cuticle is the closest thing Nematodes
have to a skeleton
• functions as support and a leverage point
for movement
• fluid in pseudocoelom serves as
hydrostatic skeleton

10. • the epidermis consists
of a mass of cellular
material and nuclei
without separate
membranes; secretes
thick cuticle that is
tough, yet flexible
• the cuticle is
periodically shed; up to
times before adult
stage

11. • Nematodes are sexual animals
• the male is generally slightly smaller than
the female, which usually displays a bent
tail
• Nematode reproduction in free-living
specimens is a very interesting process
involving six stages including an egg stage,
four larval stages (L1, L2, L3, L4), and an
adult stage.

12. • Males are dioecious in that they can have
one or two testes and can have a variety of
accessory sex organs depending on the
species
• Females give rise to eggs that are then
fertilized and laid
• Once embryos, these eggs are mature and
hatch. After four molts, they becomes
adults capable of reproduction
• During molting, a nematode will shed its
skin in order to facilitate growth. The
third L3 larval stage is normally the
infectious stage for parasitic nematodes

13. • many nematodes are
able to suspend their
life processes
completely when
conditions become
unfavorable
• resistant states in which
they can survive
extreme drying, heat,
or cold, and then return
to life when favorable
conditions return
• this is known as
cryptobiosis
• this feature is shared
between nematodes
and rotifers

14. • They live not only in almost every geographic
location on Earth, but in such extreme
habitats as ice and hot springs, as well as
living on or in almost every kind of animal
and plant alive today.
• Free-living nematodes
– soils
– sediments, where they feed on bacteria
and detritus.
• plant parasites and may cause disease in GRRRR!!!!!
economically important crops.
• animal parasites (including humans); well-known parasitic nematodes
include hookworms, pinworms, Guinea worm
(genus Dracunculus), and intestinal roundworms (genus Ascaris)

15.  Ectoparasite of plants - lives outside the plant
 Endoparasite of plants - lives and breeds inside the plant having
entered as a juvenile
 Saprophagous - juveniles and adults are free living, juveniles enter
invertebrate animal host and cause no harm, but feed on dead tissues
when the host dies.
 Zooparasitic juvenile stages only - juveniles parasitize a host organism
and then leave when it becomes adult, the adult does not feed and may
not have a functioning gut.
 Phytoparasitic juvenile, Zooparasitic adult - juvenile lives in a plant
which is taken in by the animal host when it feeds. The adult then
parasitizes the adult and infects the larvae of the host with juvenile
worms which are then ready to enter and parasitize the plant host
again.
 Zooparasitic adult females only - young live in the soil, males die after
fertilizing females in the soil, pregnant females then enter the host

16.  Common name of phylum nematoda. They are among the most
numerous of all animals.
 Round worms were given the name of nematodes because they
resemble a thread.
 In Greek, “nematos” actually means thread hence why they are
called nematodes.
 Roundworms are slender, unsegmented worms, with tapering
end. They can be microscopic or up to a meter length.
 Most roundworms are free living, inhabiting soil, soil flats, aquatic
sediments from polar to tropical regions.
 Still others are parasitic and live in host that include almost every
kind of animal and plant.
 Unlike platyhelminthes , nematodes have a digestive tract with 2
openings the body wall and the digestive tract, the body plan
called “a tube within a tube”

17.  Cylindrical shaped
 Flexible non living cuticle
 Lack of motile cilia or flagella
 Lack of photonephridia
 Muscle of body wall run only longitudinally

18.  Carnivorous
 Other free living nematodes feed on phytoplankton
such as diatoms, algae and fungi. Many terrestrial
species feed on plant roots, penetrating the cells and
sucking out the contents.
 Species that live in sediments and other aquatic
environments ingesting particles of the substrate when
they digest associated bacteria and / or organic
material.
 Others feed more directly on dead organic material
such as decomposing plants and animals or dung.
Some in these environments feed on the bacteria or
fungi that are feeding on the decomposing material.

19.  CLASS ADENOPHOREA (APHASMIDA; 12 ORDERS)
 Mainly free-living; without phasmids; amphids located
posteriorly in the head region; sensory bristles and papillae on
the head and body; excretory organ, when present, single-celled
and without collecting tubules; males without lateral extensions
of the tail region.
 Desmodora, Dioctophyme, Monhystera, Enoplus, Strongyloides, T
richinella, Trichuris.
 CLASS SECERNENTEA (PHASMIDA; 8 ORDERS)
 Mostly terrestrial or parasitic; with phasmids;
with amphids located anteriorly in the head region and opening
and opening on lateral lips; excretory system includes collecting
tubules; without somatic setae or papillae, except sometimes on
the tail of males; Males often with lateral extensions of the tail
region.
 Ancylostoma, Necator, Ascaris, Gnathostoma, Dracunculus, Filar
ia, Camallanus, Wuchereria.