Not as advanced as higher worms such as earthworms because
They lack body segmentation.
3 Nematodes contd
Unsegmented roundworms are classified into about 16000 species but the actual number of nematode species could be as high as 500000.
Range in length from microscopic to several meters long.
May be free-living or parasitic.
4 Nematode Habitat
Nematodes live in
Parasitic nematodes live within a host
Free-living nematodes live in marine freshwater or damp soil environments.
5 The Nematode lifestyles
Nematodes generally live one of two types of lifestyles free-living or parastic.
6 Free-living Lifestyle
Herbivores eat plants
Carnivores eat animals
Omnivores eat both plants animals
Saprophagous -Eat dead organic matter (from animals only) Yummy
Free-living and have the eating habits mentioned on the previous.
The free-living nematodes are important because they add organic matter to the soil and putting holes in the soil to better allow water movement through the soil.
7 Parasitic Lifestyle
Parasitic feed off of a host.
These worms feed of the blood or tissue fluids of their hosts.
We will learn about four types of parastic nematodes filarial worms hookworms trichina worms and ascaris worms.
The filarial worms cause the disease elephantitis pictured to the left.
Trichina worms cause trichinosis the horrid disease contracted from eating undercooked pig products.
8 Nematode Body Plan
Nematodes have three cell layers
Ectoderm outer tissue layer (epidermis)
Mesoderm middle tissue layer (muscle)
Endoderm innermost tissue layer (body cavity)
They are known as psuedocoelomates because they have an internal cavity that is not lined with peritoneum therefore it is not a true coelom.
They are bilaterally symmetrical as is every organism we study from here on out.
9 Nematode Epidermis
The outside of the nematode is made up of a tough flexible noncellular layer known as the cuticle.
The cuticle is secreted by epidermal cells.
It functions to
Resist penetration in free-living.
Resist enzymatic digestion in parasitic.
Maintains internal hydrostatic pressure.
The cuticle usually molts 4 times during maturation.
10 Nematode Digestive System
One way digestive system remember this means that food goes in one way and out another. Just like us.
The digestive tract is a linear progression as shown below
mouth pharynx intestines rectum anus
Food is pushed through this system by hydrostatic pressure.
11 Nematode Musculature
The nematode body wall has only longitudinal muscles.
Remember longitudinal means lengthwise so they only run from the anterior to the posterior end of the worm.
These muscles are used for movement.
When these muscles contract it causes the thrashing movements from head to tail.
They lack circular muscles so they cannot crawl as we saw the leech do on dry surfaces.
12 Excretory System
Aquatic species have ventral glands (called renettes) posterior to the pharynx that absorb waste from the pseudocoelom and empties the waste through the excretory pore.
Parasitic nematodes have a more advanced excretory system.
13 Parasitic Excretory System
Their system is known as a tubular system that develops from the renette system of the free-living worms.
The renettes unite to form two large canals known as the excretory canals that open to the outside by an excretory pore which is located by the head.
A little odd to excrete wastes near your head eh
14 Excretory System Diagram 15 Reproductive System
Most nematodes are
Dioecious two different types of reproductive cells ex. sperm egg.
Dimorphic two different sexes ex. male and female.
As you might guess they reproduce sexually.
The males are slightly smaller than the females. Why
16 Female Reproductive System
Consists of a pair of ovaries attached to an oviduct that has a swollen proximal end that forms a seminal receptacle.
Each oviduct becomes a tubular uterus and the two uteri come together to form a vagina that opens to the outside through a genital pore.
17 Male Reproductive System
Most male nematodes have only a single testis attached to the vas deferens which expands into a seminal vesicle which connects to the cloaca.
What are all these things
Vas deferens aka sperm duct releases sperm
Seminal vesicle stores sperm cells
Cloaca hole that sperm is ejected from
They also have a flap of tissue called the bursa that aids in the transfer of sperm to the female genital pore.
18 Reproductive System Diagram 19 Brief Parasitic Nematode Info.
Most common roundworm in the U.S.
Adults reside in the large intestine.
Enter humans by being eaten.
Found in the southern U.S.
Adults live in the small intestine of humans.
Enter host through the skin usually between the toes. That makes you want to walk around barefoot doesnt it
Live in humans other omnivores (like piggys)
Adults live in the small intestine of its host larvae encyst in the stomach and skeletal tissue (ouch!)
Enter host by being eaten.
20 Nematode Nervous System
Nematodes have two nerve cords in their bodies.
Ventral nerve cord runs along the belly.
Dorsal nerve cord runs along the back.
They have a central nervous system consisting of a circular brain.
The nervous system allows the nematode to detect its environment and react to it.
Aquatic nematodes have a pair of ocelli (eyes).
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