1. The Pseudocoelomate Body Plan: Aschelminthes
Chapter 11

2. Aschelminthes
Seven different Phyla grouped into either the Lophotrochozoan (those that do NOT molt) or
Ecdysozoan (those that DO molt)

3. Aschelminthes Characteristics First animal to posses a body cavity
Pseudocoelom
Distinct body cavity with no peritoneal lining and mesenteries.
Visceral (internal) organs lie free in the cavity

4. A pseudocoelom
Is a body cavity derived from the blastocoel, rather than from mesoderm
Pseudocoelom
Muscle layer
(from
mesoderm)
Body covering
(from ectoderm)
Digestive tract
Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.

5. Characteristics
Pseudocoelom – acts as an internal hydrostatic skeleton that functions in locomotion

6. Characteristics
Most have a complete tubular digestive tract (mouth-anus)
First time mechanical breakdown of food, digestion, absorption, and feces formation

7. Characteristics
Show eutely – same number of cells for each animal and for each given organ in all the animals of the species
Ex. Caenorhabditis elegans (a type of nematode) has 959 cells
Every worm in the species has 80 cells in their pharnyx

8. Nobel Prize (2002) Brenner, Sulston and Horvitz
C. elegans
Nobel Prize (2002) Brenner, Sulston and Horvitz
“Genetic regulation of organ development and programmed cell death”
Sydney Brenner
- C. elegans since 1963
Using the nematode C. elegans this year's Nobel Laureates have demonstrated how organ development and programmed cell death are genetically regulated. They have identified key genes regulating programmed cell death and demonstrated that corresponding genes exist also in higher animals, including man. The figure schematically illustrates the cell lineage (top left) and the programmed cell death (below) in C. elegans. The fertilized egg cell undergoes a series of cell divisions leading to cell differentiation and cell specialization, eventually producing the adult organism (top right). In C. elegans, all cell divisions and differentiations are invariant, i.e. identical from individual to individual, which made it possible to construct a cell lineage for all cell divisions. During development, 1090 cells are generated, but precisely 131 of these cells are eliminated by programmed cell death. This results in an adult nematode (the hermaphrodite), composed of 959 somatic cells.

9. Characteristics Microscopic to meters in length
Bilaterally symmetrical
Unsegmented and cylindrical in cross section
Most are freshwater
Osmoregulation through protonephridia (mainly in freshwater)

10. Characteristics Triploblastic Most are dioecious
No separate gas exchanges
Some cephalization is present
Cuticle present – may bear spines or scales and is useful for protection and taxonomic identification

11. Lophotrochozoan Phylum Rotifera (rota, wheel + fera, to bear)
Small animals mm
Most abundant in freshwater
About 1,000 cells (3 classes) and organs are eutelic

12. Phylum Rotifera
All have a Corona (crown)- ciliated organ for locomotion and food gathering

13. Phylum Rotifera
Posterior toes and adhesive glands called: Pedal gland- secretions aid in temporary attachment of foot to a substratum.

14. Feeding and Digestion
Feed on small microorganisms and organic material Coronal cilia brings food to mouth Food enters the Pharynx that contains a muscular organ that grinds food called Mastax

15. Feeding and Digestion
Then food passes through a ciliated Esophagus to the ciliated Stomach-complete extracellular digestion and absorption of food occurs.

16. Feeding and Digestion
Some species have ciliated Intestine that becomes Cloacal bladder- receives water from the protonephridia, eggs from ovaries, and digestive waste. Cloacal bladder opens to the outside via an Anus

18. Other Organ Systems
Protonephridia that empty into the cloacal bladder function in osmoregulation Nervous System- 2 lateral nerves and bilobed brain

20. Reproduction and Development
Some reproduce sexually Many reproduce by parthenogenesis- a type of reproduction in which females produce offspring from unfertilized eggs

21. Reproduction and Development
Females
Germovitellarium- ovary and vitellarium fuse
Males
Single testis
Eversible penis-injects sperm into the pseudocoelom of female (hypodermic impregnation)

22. Reproduction and Development
Divided into 3 classes:
class
order

23. Class Seisonidea
Females produce haploid eggs that must be fertilized and develop into either males or females. ♀ & ♂ similar in size and form Sexually reproduction only

24. Class Bdelloidea
Females are parthenogenetic (asexual)- produce diploid eggs that hatch into diploid females.

25. Class Bdelloidea
"The study of rotifers is a study of ladies, sometimes beautiful, often capricious, always fascinating.“ (Meglitsch)

26. Class Monogononta Females produce two kinds of eggs:
Amictic eggs- diploid eggs that have not undergone reduction division, cannot be fertilized & develop only into females.

27. Class Monogononta Mictic eggs- undergone meiosis and are haploid- if:
Unfertilized- develop quickly into males
Fertilized- they secrete a thick shell and become dormant for several months before developing into amictic females.

32. Ecdysozoan
Phylum Nematoda
The roundworms

33. 5 billion per acre

34. Phylum Nematoda Parasites and free-living
Lack cilia except in their sensory structures
Marine, freshwater, and soil habitats
Triploblastic, bilaterally symmetrical
Unsegmented vermiform (wormlike organism)

36. Phylum Nematoda External features Noncellular, collagenous cuticle
Can molt 4 times during maturation
Maintains internal hydrostatic pressure
Mechanical protection
Resists digestion by the host

38. Phylum Nematoda Longitudinal muscles are used for locomotion
Thrashing movements (can’t crawl like worms)

39. Phylum Nematoda Sensory organs
Amphids – chemoreceptors along the cuticle
Phasmids - chemoreceptors near the anus
Ocelli – eyespots found in aquatic nematodes

40. Feeding and Digestive System
Carnivores, herbivores, omnivores, saprobes(decomposers), or parasitic Complete digestive system mouth->buccal cavity->pharynx ->tubular intestine->rectum->anus Hydrostatic pressure pushes food thru

41. Other Organ Systems Glandular system Aquatic nematodes
Renettes – absorb nitrogenous waste
Tubular system
Parasitic nematodes
Renettes form a canal

42. Other Organ Systems Nervous system
Nerve ring from anterior to posterior
Also have neuroendocrine secretions involved in growth, molting, cuticle formation, and metamorphisis

43. Reproduction Sexual Dioecious-having separate sexes
Dimorphic-males are smaller than females
internal fertilization

44. Reproduction Males One testis
Bursa- used to insert their sperm into the female
males have ameboid sperm

45. Reproduction Females Pair of convoluted ovaries Oviducts become uterus
Several hundred to several hundred- thousand eggs per day
Ovovivparity – giving birth to larvae that hatched from an egg

46. Some Important Nematode Parasites of Humans
Ascaris lumbricoides
Enterobius vermicularis
Necator americanus
Trichinella spiralis
Wuchereria bancrofti

47. Ascaris lumbricoides
The Giant Intestinal Roundworm- The adult female worm can be over 30 cm long and 2-6 mm wide 800 million infected- most common parasitic worm disease in the world
the largest of the human intestinal nematodes. This is the most common parasitic worm disease in the world, very prevalent in tropical regions but rarely found also in our country. In the United States about 4 million people are infected. The adult female worm can be over 30 cm long and 2-6 mm wide. The female worm produces eggs per day.

48. Ascaris lumbricoides
Adults live in small intestines of humans Eggs exit with through feces Once the eggs are ingested, they hatch in intestine and travel to the lungs Larvae molt twice, they travel to the trachea where they are swallowed

51. Ascaris lumbricoides When Ascaris becomes a big problem. . .
Warning: those with weak stomachs need not continue viewing. Only for the HBO audiences!
When Ascaris becomes a big problem. . .

52. Enterobius vermicularis
Pinworm
Most common parasite in US
Adults live in large intestine
At night females migrate out of the anus and lay eggs on skin

53. Enterobius vermicularis
Human ingest eggs, hatch and molt 4 times in small intestine & migrate to large

55. Necator americanus Found in Southern US
Adults live in small intestine with teeth and feed on blood & tissue fluid
Females 10,000 eggs daily & pass out of body in feces
Hookworm

56. Necator americanus
Eggs hatch in warm moist soil and releases a small larva, the larva molts and becomes the infective filariform larva.
hookworms living in soil

57. Necator americanus
Humans become infected when filariform penetrates the skin (usually b/w toes) to reach our circulatory system
Outside defecation and walking barefoot maintains life cycle

59. Trichinella spiralis
The Porkworm Adults live in mucus of small intestine of humans and other mammals
Adult female
Adult male

60. Trichinella spiralis
Females birth young, larvae enter circulatory system and are carried to Skeletal (striated) Muscles
Larvae entering into Skeletal Muscle cells

61. Trichinella spiralis
Larvae encyst in muscles & remains infective for many years

62. Another host must ingest infective meat to continue the life cycle

64. Trichinella spiralis
Humans become infected by eating improperly cooked pork products Larvae encyst in stomach move to small intestine molt 4 times, turn into Adults

65. Wuchereria bancrofti
The Filarial worms In tropical countries over 250 million human infected
Lymphatic vessels return tissue fluids to circulatory system

66. Wuchereria bancrofti
Thread-like worms that live in the Lymphatic System, block the vessels This causes enlargement of various appendages: Elephantiasis
An Adult female Wuchereria bancrofti is about mm long and mm in diameter, whereas a male is about 40 mm long and 0.1 mm in diameter.

67. Elephantiasis
Warning: Pictures not for everyone!

68. Wuchereria bancrofti
Adults copulate produce microfilariae. The microfilariae released into the blood stream
A microfilaria is about µm (micrometers) long and µm thick

69. Wuchereria bancrofti
Mosquito (intermediate host) feeds on human (definitive host) ingest microfilariae and larvae molts 2 times Mosquito bites another human it injects 3rd stage larvae into human blood, molts, enters lymphatic system

71. Other Filarial Worms
Dirofilaria immitis in US parasite of dogs Adult worms live in heart, large arteries, and lungs Heartworm disease- fatal to dogs, unless give preventative medicine

73. Phylum Nematomorpha Phylum Nematomorpha Characteristics 250 species
Horsehair worms
Adults are free-living
Juveniles are parasitic in arthropods
No distinct head
Dioecious