1. Platyhelminthes & Nematoda
The un-segmented worms

2. Earland

3. GENERAL CHARACTERISTICS
18,500 species
Simplest animals with bilateral symmetry
Exhibit some cephalization
Three germ layers (i.e.:triploblastic)
Acoelomate: no mesodermal lined cavity
3 classes parasitic, 1 class free-living

5. Flatworm Organ Systems
Biology: Life on Earth (Audesirk)
Flatworm Organ Systems
Pharynx
(a) Digestive System
Excretory Canal
Gastrovascular Cavity
Excretory Pore
(b1) Excretory System
Flatworms such as planarians have well-developed organ systems. (a) The elaborately branched digestive system, the centrally located ventral pharynx, and eyespots in the head are clearly visible. (b) (Left) The excretory system consists of branching tubes that conduct excess fluid to the outside through numerous pores. Cilia keep the fluid moving. (Right) The nervous system of flatworms shows clear cephalization, with eyes and a brain composed of ganglia cells in a well-defined head. Ladderlike nerve cords carry signals through the rest of the body.
(b2) Nervous System
Nerve Cord
Brain
Chapter 22
Chapter 22

6. ESSENTIAL FUNCTIONS Because they are flat, flatworms have no
specialized circulation or respiration. They simply use diffusion across body wall.
In addition to diffusion, flatworms use protonephridia (simple kidney-like structure) to osmoregulate (control water balance). Within the protonephridia, there are beating cilia which draws fluid through. Because this looks like a flickering candle, these cells are dubbed flame cells.

8. Digestion
Digestion: 1 way (like us!): Pharynx is on underside of flatworm and sucks food into the gastrovascular cavity.
Intestine branches the length of the flatworm, so digested food can be delivered to all body tissues

9. Reproduction & Movement
Reproduction: Most flatworms are simultaneous hermaphrodites. Each individual can function as both male and female. Although a single individual cannot fertilize itself.
Movement: Secrete mucus and use cilia on their epidermal cells to glide across bottom, as well as muscle contractions which allows them to twist and turn.

10. Classes of Flatworms
Class Turbellaria-planarians, free-living, non-parasitic, live in moist environments
Class Trematoda-flukes, parasites that absorb nutrients from the body of a host harming it, may have more than 1 host
Class Cestoidea-tapeworms, parasitic, live inside 1 or more hosts, contain flat segments each with reproductive organs
Earland

11. Class Tubellaria Class Turbellaria 16% of flatworms
Most species are free living.
Most live in marine environments
Diet includes: bacteria, algae and invertebrates
Considerable powers of regeneration in some species

12. Class Cestoda Class Cestoda Endoparasites: Internal parasites
Celebrity cestoda: Tapeworm
Hosts are primarily vertebrates.
Extremely high specialization for parasitic lifestyle.
No ciliated epidermis.
No mouth, instead has scolex studded with hooks and suckers.
Scolex attaches to the intestinal wall

13. An intermediate host is required, such as a cow, fish or pig.
It is estimated that 135 million people are infected with tapeworms.
Symptoms include: Nausea, weakness, loss of appetite, abdominal pain, diarrhea and weight loss
Most of the body is made up of repeating reproductive segments called proglottids.
A single proglottid may contain over 100,000 eggs!
 An intermediate host is required, such as a cow, fish or pig.

14. Class Trematoda Class Trematoda Parasitic worms known as flukes.
Some are ectoparasites parasites, living on skin, mouth and gills of host.
Celebrity Tremadode: Schistosoma, humans are primary hosts.

16. Schstoma Life Cycle
Schistosoma lay so many eggs in blood vessels of the intestine that blood vessels burst and eggs and blood are released into intestine.

17. Pseudocoelomates
Nematoda
Rotifera

18. How do the Pseudocoelomates fit in?
Rotifera
Nematoda
the pseudocoelomates
Platyhelminthes
Nemertea
Cnidaria
Porifera
unknown
common ancestor

19. Pseudocoelomates
There are 9 different phyla that are classified as pseudocoelomates.
We are only covering 2 phyla:
Nematoda
Rotifera

20. Pseudocoelomate Characteristics
Organ level of organization
Tissues are organized to for organs which are used to accomplish physiological functions
Triploblastic
3 Germ Layers
endoderm
mesoderm
ectoderm
3 Tissue Layers
gastrodermis
mesoderm
epidermis

21. Pseudocoelomate Characteristics
“false” body cavity
ectoderm
pseudocoelom
mesoderm
Gut
endoderm
the pseudocoelom is lined by mesoderm on ONE side only

22. Pseudocoelomate Characteristics
the pseudocoelom
is a closed, fluid filled cavity
contains digestive, excretory, and reproductive structures
the fluid within acts as a circulatory system
the fluid within acts as a hydrostatic skeleton against which the muscles work

23. Pseudocoelomate Characteristics
Bilateral Symmetry
with anterior and posterior ends
Cephalization
concentration of sensory organs in the head of the animal

24. Pseudocoelomate Characteristics
Digestive System
complete (they have an anus!)
some regional specialization
Circulation System
no system (or organs)
performed by the pseudocoelom fluid

25. Pseudocoelomate Characteristics
Eutely
each individual of a species has the same # of cells
growth occurs by cells getting bigger rather than dividing

26. Phylum Nematoda the roundworms
1st phyla we will talk about and what we will cover in the lab today is…

27. Nematodes
Most abundant living animals include the roundworms –closely related to insects than others.
Cylindrical and bilateral body, a complete gut and a false coelom filled by reproductive organs. Have flexible cuticle – undergo repetitive molting as it grows.
Free living sp that are decomposers and agricultural pests.
Others are parasites to humans, dogs and insects.

28. Roundworms-Phylum Nematoda
Roundworms-small, cylindrical worms with pointed heads and tapered tails
3 tissue layers
Complete digestive tract with mouth and anus
Digestion highly specialized
Free-living and non-parasitic roundworms are the most abundant but parasitic types are hookworm, pinworm, threadworm and trichinosis
Many are introduced through poorly cooked pork or walk barefoot in infected areas
Earland

29. The Invertebrate Phyla: Nematoda (Round Worms)
Advanced gastrovascular cavity
Tubular
Two openings
Advanced sensory "ganglionic brain"
Lack circulatory and respiratory systems
Depend on diffusion for gas exchange
Sexual reproduction
Most are harmless - Some parasitic
Chapter 22

30. Physiology Life Style Digestion Free-living parasitic
complete system (have an anus)
some regional specialization (e.g. an esophagus)

31. Physiology Skeletal system Cuticle
fluid in pseudocoelom acts as a hydrostatic skeleton
Cuticle
covers body (secreted by epidermis &composed mostly of collagen)
functions as a primitive external skeleton

32. Physiology Movement longitudinal muscles ONLY
(results in “whiplike” motion)
No external/internal cilia
 even sperm don’t have flagella

33. Physiology Circulatory system Excretion Nervous system
cephalization, cerebral ganglia
dorsal and ventral nerve cords
Circulatory system
No system (no organs)
performed by fluid in pseudocoelom
Excretion
Renette glands

34. Physiology Reproduction Sexual usually dioecious
often the sexes are sexually dimorphic
(males and females look different)
Males often have a spicule
at the end of their tail used to insert their sperm into the female

35. Physiology Reproduction Sexual usually dioecious
often the sexes are sexually dimorphic
internal fertilization
males have ameboid sperm

36. Ecology
There are >12,000 species that are found in almost all habitats (marine, freshwater, underground, inside plants and animals, etc…).
They are also incredibly abundant. For example:
a m² of soil may contain >4 million nematodes
a decomposing apple may contain >90,000 nematodes of a single species

37. parasite of soybean plants parasite of tomato plants
Ecology
Many nematodes are important parasites of both plants and animals.
parasite of soybean plants
parasite of tomato plants

38. Parasites Eye worm (Loa loa): transmitted by fly bites
larvae go through bloodstream
adults live in subcutaneous tissue

39. Parasites Intestinal roundworm (Ascaris):
transmitted by contaminated food
adults live in small intestine
it’s estimated that 20% of world’s population is infected (~1.3 billion people)
this intestine was completely blocked

40. Parasites Guinea worm (Dracunculus medinensis):
transmitted by infected copepods in drinking water
larvae move into the body cavity
female adult migrates to the subcutaneous tissue, causes an ulcer/blister, and releases eggs through hole when host comes in contact with water

41. Guinea worm

42. Parasites Guinea worm (Dracunculus medinensis):
traditionally removed by winding the worm around a matchstick over the course of several days
this may be the basis for the Caduceus symbol used in the medical field

43. Parasites Trichinella spiralis: causes Trichinosis
transmitted by eating undercooked pork
juveniles encyst within host muscle cells
juvenile
Host muscle cell

44. Parasites
Heartworms (Dinofilaria immitis):

45. Ecology
The study of the model nematode C. elegans has resulted in important discoveries in genetics and development.

46. Phylum Rotifera the rotifers
1st phyla we will talk about and what we will cover in the lab today is…

47. The “wheel” animals

48. Physiology Feeding have a “crown” of cilia called a corona
the corona creates a
current to bring food into
the mouth

49. Physiology Feeding have a specialized feeding structure called the:
mastax-trophi complex
modified jaws
within the mastax
a modified
muscular pharynx

50. Looking down into the corona….

51. Physiology
Some of the trophi (jaws):

52. Physiology Life Style Digestion Free-living
complete system (have an anus)
some regional specialization (e.g. mastax-trophi complex)

53. Physiology Movement Skeletal system the corona
fluid in pseudocoelom acts as a hydrostatic skeleton
Movement
the corona
pedal glands (produce adhesive), as well as foot and toe (spurs) for attachment to substrate

54. Physiology Circulatory system Excretion Nervous system
cephalization, cerebral ganglia
dorsal and ventral nerve cords
Circulatory system
no system (no organs)
performed by fluid in pseudocoelom
Excretion
protonephridia and flame cells
cloacal bladder (collects wastes)

55. Physiology Sexual Reproduction
complex life cycle with different types of eggs
usually dioecious but in some groups, males are absent (parthenogenesis)
Parthenogenesis:
unisexual reproduction where females produce offspring from unfertilized eggs (virgin birth)

56. Physiology Amictic eggs Mictic eggs haploid (meiotically produced)
produced after some sort of environmental stimulus (eg. high density, change in temperature)
if unfertilized, develop into haploid males
if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females
diploid (mitotically produced)
can’t be fertilized
develop into diploid, amictic females

57. Ecology
There are ~1500 species. Although they are found mainly in freshwater habitats, there are a few marine rotifer species and a couple of species are even found in mosses!
Because of the reduced role of males in reproduction, most males are incapable of feeding and do not even have a digestive tract (they are just there for sperm delivery!).
Males have never been recorded in Bdelloid rotifers. This means they haven’t had sex in millions of years!

58. Here are some of the other pseudocoelomate phyla

59. Kinorhyncha
Loricifera
Nematomorpha
Priapulida

60. Acanthocephala
Gastrotricha
Entoprocta

61. How do the Pseudocoelomates fit in?
Rotifera
Nematoda
mastax-trophi
no cilia
corona
longitudinal muscles only
pseudocoelom
Platyhelminthes
Nemertea
Cnidaria
complete digestive system
Porifera
organ level of organization
triploblastic
unknown
common ancestor