1 Trematoda - morphology, classification and life cycle

Question 1

Phylum:
Subphylum:
Class:
Orders: (5)

Answer 1

Phylum: Platyhelminthes
Subphylum: Trematoda
Class: Dignea
Orders: Echinostomida, Amphistomida, Plagiorchida, Opistorchida, Strigeidida

Question 2

What are the Classes of Dignea?

Answer 2

1. Echinostomida
2. Amphistomida
3. Plagiorchida
4. Opistorchida
5. Strigeidida

Question 3

What are Platyhelminths?

Answer 3

Flatworms

Question 4

What are Dignea?

Answer 4

Flukes

Question 5

General Morphology

Answer 5

• Ventrally flattened and oval shaped, vary in thickness
• Powerful oral sucker - surrounding the mouth
• Acetabulum - fixation function, location(midventral) and shape vary
• Holdfast - behind acetabulum (additional adhesive organ)
• Tegument - Spiny protective outer layer

Question 6

Size

Answer 6

Majority = 2-15mm
Smallest Dignea = 0.16mm
Largest Dignea = several meters

Question 7

Nervous System

Answer 7

• Pair of Cerebral ganglion (anterior)
• 3x Nerve trunks, branch like a ladder

Question 8

Digestive system

Answer 8

Well developed
* Mouth -surrounded with oral sucker
* Pharynx
* Oesophagus
* 2x Intestinal caeca

Question 9

Excretory system

Answer 9

• Protonephridial type
• Flame cells
• Collecting ducts - imp. larval stage (tax)
• Excretory bladder - V or Y shape (tax)

Question 10

Reproductive system

Answer 10

• Hermaphrodites - except Schistosomes = self fertilization, some do cross-fertilization
• Male: 2x Testes, vas efference, vas deferent, genital pore, cirrus pouch, sperm storage, prostate, cirrus (penis) - -invaginated or evaginated, naked or covered with spines
• Female: 1x Ovary, oviduct, seminal receptacle, Laurels canal (vestigial vagina), Vitelline gland (Yolk in cells), Mehlis glands, uterus, metraterm (distal muscular end of uterus), genital pore
• The genital pores of male and female open together in genital atrium

Question 11

What are the different body types (7) of Dignea with position of fixation organs

Answer 11

1. Distome - os=anterior end, acet= midventral
2. Amphistome - os=anterior end, acet=posterior end (large)
3. Monostome = only oral sucker anterior
4. Gasterostome - ?
5. Holostome - os=anterior end, acet=prox 3rd above Tribocytic organ
6. Echinostome - os=anterior end (surrounded by collar of spines), acet=midventral
7. Schistosome - both male and female os=anterior, acet=slightly below os

os = Oral sucker
acet = Acetabulum

Question 12

Ovary and Testes shape and positions

Answer 12

Shape
* Oval
* Lobed
* Branched

Position
* Ovary = above, between or below testes
* Testes = Side by side, one above the other or oblique position

Question 13

Larval stages (5)

Answer 13

1. Miracidium - from egg, free in water
2. Sporocyst - germinal sac, can become daughter sporocyst, redia or cercaria
3. Rediae - have embryos that can become daughter redia or cercaria
4. Cercariae - juvinile stage, free-living (short)
5. Metacercariae - ** Infective stage**, encysts on IH or aquatic vegetation (not in blood flukes)

Question 14

Miracidium

Answer 14

• Ciliated, non-feeding
• Develops inside egg and hatch into environment (water)
• Free swimming, active to find suitable host (Mollusc)
• Can only live free for few hours
• Cilia helps to locate and penetrate the IH
• Always present in LC

Question 15

Sporocyst

Answer 15

• Miracidium changes into Sporocyst when entering the IH
• Becomes germinal sac
• No cilia, gut or mouth
• Absorb nutrients
• Develop into daughter sporocyst, redia or cercaria

Question 16

Redia

Answer 16

• Exit from Sporocyst and migrate to IH gonad
• Rudementary digestive system
• Mouth, pharynx and short gut
• Embryos within develope into daughter redia or cercaria

Question 17

Cercaria

Answer 17

• Juvenile stage
• Morphology varies with species (e.g. Furcocercaria-Schistosome)
• Free-living, for brief periods until finding a FH or new IH
• Always present in LC

Question 18

Metacercaria

Answer 18

• Infective stage for FH
• Encysted on IH or aquatic vegetation, sticks or free-living in water
• Excyst once inside FH
• Not in Blood flukes

Question 19

Life cycle stages (4)

Answer 19

1. Embryogony
2. Parthenogony
3. Cystogony
4. Maritogony

Question 20

IH

Answer 20

• 1 or more IH can be found in LC
• Molluscs (Asexual reproduction)

Question 21

FH

Answer 21

• Vertebrates (sexual reproduction)

Question 22

Embryogony

Answer 22

• Egg to Miracidium
• Hatches in water or after eaten by IH
  -In water = Light and osmotic pressure are important factore
  -In IH = Pressure and CO2 pressure are important factors

Question 23

Parthenogony

Answer 23

• Development inside IH
• Transform from Miracidium to Sporocyst, Redia or Cercaria
  1. Entering the IH, Miracidium loses it cilia and transforms into Sporocyst (germ cell sac)
  2. Germ cells either divide asexually and become Daughter Sporocysts or form new larval stage Redia or Cercaria
  3. Redia may develop Daughter Redia or Cercaria
  4. Cercaria leave the sporocyst or Redia and migrate out of IH
  5. Cercaria may penetrate FH (Schistosoma), penetrate a 2nd IH (encyst) or attach to aquatic vegetation (encyst)

Question 24

Cystogony

Answer 24

• Development of Metacercaria
• Encysted, Infective stage (not in blood flukes)
  1. After Cercaria exit IH they begin to form Metacercaria or find next host
  2. Cercaria first step to encyst is to cast off its tail
  3. Will encyst and attach itself to aquatic vegetation (or in 2nd IH)
  4. Waits to be ingested by FH
• 3 broad groups of Metacercaria
  -Encyst in the open on vegetation, can infect FH almost immediately = Fasciola spp.
  -Sp. that do not grow in IH but need several days to develop to infect FH = Echinostomatidae
  -Sp. that grow before entering resting stage in 2nd IH, need weeks to develop = Diplostomidae

Question 25

Maritogony

Answer 25

* Development in the FH 1. After 2nd IH or aquatic vegetation with Metacercaria is ingested by FH, the Metacercaria will excyst in the intestine 2. Migrates to the final site and matures into adult (liver, lung, circulatory system) Examples: -Dicrocoelium dendriticum: reach liver by bile ducts -Faciola hepatica: burrows through gut wall into peritoneal cavity to liver -Clonorchris sinensis: burrows through gut wall and is carried to liver by hepatoportal system Paragonimus westermani: penetrates gut wall, develops in abdominal wall for 1 week, re-enters abdominal cavity,goes through the diapragma to the lungs

Question 26

# Classification Echinostomida * Family (2) * Genus (3+5)

Answer 26

Family = Fasciolidae Genus = **Fasciola, Fascioloides, Fasciolopsis** Family = Echinostomatidae Genus = **Echinostoma**, Euparyphium, Echinoparyphium, Hypoderaeum, Philophtalmus

Question 27

# Classification Amphistomida * Family (3) * Genus (5+3+3)

Answer 27

Family = Paramphistomidae Genus= **Paramphistomum**, Calicophoron, Cotylophoron, Gigantocotyle, Orthocoelium Family = Gastrodiscidae Genus = Gastrodiscus, Gastrodiscoides, Homalogaster Family = Gastrothylacidae Genus = Gastrothylax, Carmyerius, Fischoederius

Question 28

# Classification Plagiorchida * Family (4) * Genus (1+3+1+3)

Answer 28

Family = Plagiorchidae Genus = Plagiorchis Family = Dicrocoelidae Genus = **Dicrocoelium**, **Eurytrema**, Platynosomum Family = Prosthogonimidae Genus = **Prosthogonimus** Family = Troglotrematidae Genus = Troglotrema, **Paragonimus**, Nanophyetus

Question 29

# Classification Opistorchiida * Family (2) * Genus (2+2)

Answer 29

Family = Heterophyidae Genus = Heterophyes, Metagonimus Family = Opistorchiidae Genus = **Opistorchis**, Metorchis

Question 30

# Classification Strigeidida * Family (3) * Genus (7+3+2)

Answer 30

Family = Schistosomatidae Genus = **Schistosoma**, Bilharziella, Trichobilharzia, Orientobilharzia, Ornithobilharzia, Heterobilharzia, Austrobilharzia Family = Strigeidae Genus = Apatemon, Cotylurus, Notocotylus Family = Diplostomidae Genus = **Diplostomum, Alaria**