Nematoda

Question 1

Why is Nematoda called Nematoda

Answer 1

Because of thread-like appearance

Question 2

Body characteristics of Nematodes

Answer 2

• head has paired lateral sensory organs from cilia and opening to the outside via a small pore
• body is elongated and round “roundworms”
• ubiquitous, externally unsegmented, acoelomate and pseudocoelomate worms
• tapered at both ends
• covered by thick, multilayered cuticle of collagen secreted by epidermis
• small (1-2mm) but parasitic ones can reach several centimetres

Question 3

Habitat of Nematodes

Answer 3

Terrestrial and aquatic

Aquatic: fresh or marine, abundant in deep sea, hundreds to thousands per meter below ocean surface. Could be up to 1M per square meter in freshwater and 3M in marine

Terrestrial: top soil or deep soil or gold mines

-rotten apple could hold up to 90,000

Question 4

Nematodes are one of the most ________ multicellular animals still in existence

Answer 4

Abundant

Question 5

Lifestyle of nematodes

Answer 5

• most are free living in soil or water

- others are parasites to vertebrates, invertebrates and plants

Question 6

Why are nematodes in own phylum?

Answer 6

• originally placed in Aschelminths because of cuticle and thought to be monophyletic
• also thought to be placed with Arthropoda simile phylum’s because of molting
• recent molecule finding shows nematodes originated from different ancestry than aschelminths

Question 7

Pseudocoel fluid when present may function as a _______ in nematodes because they lack a _______

Answer 7

Circulatory medium
Some contain hemoglobin

But lack closed circulatory system

Question 8

Nematodes organs are never wrapped by the mesodermal lining of the coelomic cavity called a

Answer 8

Peritoneum

Question 9

Nematodes multilayered cuticle characteristics

Answer 9

• epidermis is syncytial; nuclei not separated by complete cell membranes
• cuticle in some composed of highly complex network of fibres that are virtually inelastic; causing ability to bend, stretch and shorten the cuticle
• cuticle permeable to water and gases; gas exchange across entire body
• cuticle selectively permeable to ions and organic substances for maintaining a stable internal and external environment

Question 10

How often do nematodes molt?

Answer 10

Shed their cuticle periodically (molting); 4x between juvenile and adult stages

Because juvenile stages are morphologically distinct between each judge illy stages and the adult

Question 11

Eutely

Answer 11

Special kind of growth where an organism grows by increasing the size of individual cells, rather than in cell number.

Common in tardigrades, rotifiers and nematodes

Question 12

Parasitic nematode molting

Answer 12

• first 2 stages are free-living, forming envelope prior to 2nd molt
• exsheathment (releasing the external surface covering of the worm known as sheath), followed by last 2 molts only occurs after ingestion by definite host
• in definite host, the sheath is replaced by a microvillar surface; facilitating nutrient absorption from the host gut

Question 13

Nematode musculature

Answer 13

-nematode body packs circular muscles; which separates them from other vermiform (worms); places great limitations on their locomotory potential in that, for example, they cannot generate peristaltic waves of contraction

Question 14

Nematode internal pressure and locomotion

Answer 14

• turgid pseudocoel: ability to generate a substantial hydrostatic pressure within the paeudocoel
• high pressure generated by rigidity of the cuticle and the constant partial contraction of the musculature, trying to compress an incompressible fluid
• high internal pressure gives the nematode a very circular cross section which makes it roundish

Question 15

Nematode movement

Answer 15

• move by contracting longitudinal muscles on each side in an alternate manner creating a series of sinusoidal waves which propel them forward
• contraction of one part of the muscle causes bending and stretching on other side of the body
• muscle antagonism occurring on different part of the body caused pressure changes transmitted through hydrostatic skeleton which controls movement

Question 16

Nematode digestive system

Answer 16

Possess a straight digestive system, with a mouth (stoma) at anterior end leading in sequence through a muscular pharynx , intestine, and rectum, and then an anus located near the body posterior end

• pharynx added lubricants and digestive enzymes to the food as well as kept the gut lumen open against the high pressure of the pseudocoel
• digestion mainly extracellular, and nutrients are absorbed by the very thin wall (only one cell thick) of the intestine. Wastes are voided from the anus at intervals, about once every one or two minutes

Question 17

Nematodes lack _____ and _____ systems

Instead…

Answer 17

Respiratory and excretory

Metabolic wastes are apparently discharged along with other materials leaving the gut, or they diffuse across the body wall

Question 18

Renette

Answer 18

A hypothesized excretory structure which acts as a nephritis in the nematode in eliminating metabolic wastes

Question 19

Amphids

Phasmids

Answer 19

Anterior chemosensory organ lined with non-motile cilia called sensillae in nematodes

Posterior chemosensory organ in nematodes

Question 20

Cephalic and caudal papillae

Answer 20

Sensory structures present at the anterior and posterior ends, respectively in nematodes, containing modified cilia for sensory role

Question 21

Pheromones

Answer 21

Despite nematodes small size, various species are known to respond to temperature, light, mechanical stimulation and a variety of chemical cues, including those produced by other individuals of the same species

Question 22

Setae in nematodes role

Answer 22

Mechanoreceptor

Question 23

Nematode reproduction

Answer 23

• mostly dioecious (separate sexes) and individuals copulate so fertilization in internal
• others can reproduce by parthenogenesis, without the need for mating partners

Question 24

Nematode development

Answer 24

• lack free-swimming larval stages, young animals emerge from their sturdy egg coverings as miniature adults
• many can enter stage of arrest called dauer larva, at the second molt. These are basically inactive and have low metabolic rates and cannot feed. May lie for many months until conditions improve which then normal development resumes and final 2 molts occur
• Eutely

Question 25

Parasitic nematodes

Answer 25

• can infect plant roots, leaves, stems and shoots causing poor growth, yield and death
• can infect wild, domestic and agricultural animals causing poor health, reduced productivity and death
• parasitize cats, dogs, and many domestic animals of economic importance

Question 26

2 groups of nematodes well known to humans

Answer 26

Hookworms and pinworms

-damage done generally indirect, resulting from competition with host for nutrients

Question 27

Blood and nutrient depleting nematodes

Answer 27

One hookworm for example, may imbile more than 0.6 ml of blood per day. So 100 hookworm infection loses 60ml of blood daily!!

Question 28

Nematode Developmental migration in host

Answer 28

Most nematodes that parasitize animals make extensive migrations during their development within the host, from intestine, to liver, to heart, to lungs, to esophagus and back to intestine which can lead to damage in intestinal wall, lungs and eyes

Question 29

Health effects of nematodes

Answer 29

• overall, nematodes are known to infect 1/2 the worlds population
• Ascaris lumbricoides which causes malnutrition infects 1B worldwide and can cause death
• Necator americanus (hookworm) infects 1.3B worldwide and causes intestinal disorders and malnutrition and death if organs and tissues are blocked with large number of worms

Question 30

Hookworm Life (Necator americanus)

Answer 30

• single host=humans
• once in human host, the parasite undergoes an extensive internal migration before ending up in the hosts intestine, where it matures.
• mature worms in host, more and female releases fertilized eggs which pass out in hosts feces to the soil
• eggs hatch and undergo 2 molts to reach 3rd juvenile stage which is infective to man
• humans gets infected by walking bare-footed on worm-contaminated soil
• 3rd stage able to penetrate the hosts skin to establish an infection

Question 31

Life of a pinworm (Enterobius vermicularis)

Answer 31

• infects particularly children
• no intermediate host
• juevenilles often exhibit an impressive migration within the host before reaching their final location, in the hosts large intestine and colon
• mature female deposit fertilized eggs at the hosts anus and then die, releasing more eggs
• embryos transmitted to new hosts on the child’s hand or through the air
• embryos remaining in the hosts anal region emerge from their capsules after the second molt and migrate up the child’s intestinal tract to reinfect the same host.

Question 32

Life of Guinea worm (nematodes)

Answer 32

• parasite lives just beneath skin in humans, releasing an ulcer-producing secretion
• when skin contacts water, nematodes protrude it’s posterior end through the sore and ejects a considerable number of young from its anus!
• requires intermediate host: juveniles cannot reinfect humans directly but must first by ingested by a species of microscopic aquatic crustacean, a copepod
• humans become infected by drinking water contaminated with these crustaceans
• parasites liberated from intermediate host, migrate through intestinal wall of the primary host and into the hosts connective tissue

Question 33

How to stop lifecycle of nematodes

Answer 33

• always wash your hands and fruits!!!
• avoid drinking polluted water! Especially in tropics!!!
• avoid direct skin contact with contaminated soil
• improve hygiene

Question 34

Beneficial nematodes

Answer 34

-free-living nematodes are important S follows

• important protein source for aquaculture and poultry
• important ecological role in nutrient recycling
• study of nematode caenorhadditis elegans have provided lots of insights in gene regulation and functions