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Phylum Nematoda. AKA Unsegmented roundworms. Nematodes. Advancements over flatworms: Has a two-hole digestive tract. Not as advanced as “higher” worms, such as earthworms because: They lack body segmentation. Nematodes, cont’d.
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Phylum Nematoda AKA Unsegmented roundworms.
Nematodes • Advancements over flatworms: • Has a two-hole digestive tract. • Not as advanced as “higher” worms, such as earthworms because: • They lack body segmentation.
Nematodes, cont’d • Unsegmented roundworms are classified into about 16,000 species, but the actual number of nematode species could be as high as 500,000. • Nematode facts: • Colorless • Range in length from microscopic to several meters long. • May be free-living or parasitic.
Nematode Habitat • Nematodes live in: • Parasitic nematodes live within a host • Free-living nematodes live in marine, freshwater, or damp soil environments.
The Nematode lifestyles • Nematodes generally live one of two types of lifestyles: free-living or parastic.
Free-living Lifestyle • Eating habits: • 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 slide. • 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.
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. Interesting tidbits: The filarial worms cause the disease elephantitis, pictured to the left. Trichina worms cause trichinosis – the horrid disease contracted from eating undercooked pig products. Parasitic Lifestyle
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.
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.
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.
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.
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.
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?
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?
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.
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.
Brief Parasitic Nematode Info. • Pinworms • Most common roundworm in the U.S. • Adults reside in the large intestine. • Enter humans by being eaten. • Hookworms • 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, doesn’t it? • Trichina • Live in humans & other omnivores (like piggys) • Adults live in the small intestine of it’s host; larvae encyst in the stomach and skeletal tissue (ouch!) • Enter host by being eaten.
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).
