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Lab 5 Appendix: Platyhelminthes and  Acanthocephalans

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The Phylum Platyhelminthes contains both the trematodes and cestodes. The trematodes (flukes) have an incomplete digestive tract (a mouth but no anus) and have no body cavity, the organs being imbedded in the parenchyma of the body. There are 2 subclasses of parasitic flukes: the Monogenea, whose members are parasitic only as adults and the Digenea, whose members have two or more hosts in their life cycle, and the first host is a mollusk.

The Cestodes (tapeworms) have no mouth, as adults they live in the small intestine of their hosts and absorb nutrients through their tegument (external surface). The tapeworm life cycle involves an intermediate host. In many species the larval stages cause more pathology than the adult worms.

The Phylum Acanthocephala contains parasites, which as adults, lack a digestive tract and live in the small intestine of their hosts. As the name suggests, they have a spine-covered proboscis at their anterior end (they are also known as "thorny headed worms"). Although many different species are found in wildlife, only one species is a parasite of domestic livestock (pigs).


Objectives Checklist

Be able to identify the following trematode eggs:

  1. Any trematode egg  (A brown egg with an operculum is considered a trematode egg or a trematode-like egg.)
  2. Fasciola hepatica   (the operculum, the size and the host should be sufficient to identify this egg).
  3.  Dicrocoelium dendriticum  (the operculum, the size and the host should be sufficient to identify this egg).
  4. Paragonimus kellicotti (the operculum surrounded by a thick ring and the size should be sufficient to identify this egg).
  5. Echinococcus spp. and Taenia spp. (Small (35 - 45 um) brown eggs with striated border).
  6. Dipylidium caninum (expressed from a proglottid, they will be in packets).
  7. Anoplocephalids - Anoplocephala spp.and Moniezia spp. (Triangular or square eggs).

Be able to identify the adults of the following:

    8. Fasciola hepatica   (by size, shape and location within the host).

    9.  Dicrocoelium dendriticum   (by size, shape and location within the host).

    10.  Fascioloides magna  (by size, shape and location within the host).

    11.  Paramphistomum spp. -  (by size, shape and location within the host).

     12.  An acanthocephalan  (a predilection site in the small intestine, and the presence of a anterior proboscis covered with spines coupled with the lack of suckers on the anterior end is enough to identify an adult acanthocephalan.)

    13. Anoplocephala perfoliata (by the size, shape and predilection site)

Be able to identify the proglottids of:

  14.  Taenia spp.  (When gently flattened they are square to rectangular.)

  15.  Dipylidium caninum (When gently flattened they pinch in at the ends - “cucumber seed” shaped.)

Lab Exercises


Class Trematoda

Subclass Monogenea

Fish: Gyrodactylus sp.
The adults of this monogenean are ectoparasites of fish.

Subclass Digenea

Large Animal Flukes

Sheep: Fasciola hepatica
These flukes live in the bile ducts.

Fasciola hepatica egg Egg measures 140 X 80 Ám and has an operculum at one end.


Fasciola hepatica immature adults Fasciola hepatica adults
Fasciola hepatica
Immature adults. 
Fasciola hepatica
Adults:  Note the size and the
cone at the anterior end.

Fasciola hepatica miracidium Limnea snails
Fasciola hepatica miracidium

This is the stage that hatches from the egg and invades the snail.  The cilia enable the miracidium to swim and the eyespots allow it to detect light and the direction of the light.

Limnea sp.  

This snail is the intermediate host for Fasciola hepatica.


Fasciola hepatica redia Fasciola hepatica cercaria Fasciola hepatica metacercaria
Fasciola hepatica

Redia:   This stage will feed on snail tissue. Fasciola hepatica has 2 generations of redia, the germinal cells of the second generation will develop into cercariae.

Fasciola hepatica

Cercaria:   This is the stage that leaves the snail and encysts on vegetation.

Fasciola hepatica

Metacercaria:   This is the stage of Fasciola hepatica infective to sheep.

Click here to link to the Fasciola hepatica life cycle.

Deer: Fascioloides magna
A parasite of deer which causes an extensive amount of hepatic pathology in sheep, but little in cattle.

Fasciola magna Fascioloides magna

In deer the adult worms are encapsulated in the liver, but the capsule is connected to the bile duct to allow for the passage of eggs.  In cattle there is no opening to the bile duct and in sheep the worms wander through the parenchyma of the liver.

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Sheep: Dicrocoelium dendriticum
These small (1 cm) flukes are found in the bile ducts.

Dicrocoelium dendriticum adult Dicrocoelium dendriticum histology Dicrocoelium dendriticum egg
Dicrocoelium dendriticum

Adults from the bile duct of a sheep.  Note the size and lack of a "cone" at the anterior end. 
Compare to Fasciola hepatica.

Dicrocoelium dendriticum

Adult: stained to show internal organs.

Dicrocoelium dendriticum

Egg:   About 42 X 28 µm, with an operculum that is hard to see .

Sheep and cattle: Paramphistomum cervi
The small, conical fluke found in the rumen.

Paramphistomum cervi Paramphistomum sp.

Adults:  From the rumen of a cow.  Note the "plump" nature of the body, they are not flat like the other flukes.

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Small Animal Flukes

Dogs and cats: Pragonimus kellicotti
Lung fluke usually found in fibrous cysts in the lung.

Paragonimus kellicotti egg Paragonimus kellicotti stained Paragonimus kellicotti
Paragonimus kellicotti

Egg:   measures about 100 X 50 µm and has a collar or ridge around the operculum.

Paragonimus kellicotti

Adult:   This specimen has been flattened and stained to show the internal organs.   These flukes are,  like Paramphistomum sp., round in cross section (see the next image).

Paragonimus kellicotti

Adults are found in pairs in cysts in the lung parenchyma of the definitive host.  The second intermediate host is a crayfish.

Dogs and cats: Platynosomum fastosum
Adults measure 4 to 8 mm long and 1.5 to 2.5 mm wide and are found in the bile and pancreatic ducts of cats (and rarely dogs) in the Southeastern USA and the Caribbean. 

Dogs and racoons: Heterobilharzia americana

Schistosoma mansoni
Schistosoma mansoni egg
Schistosoma mansoni

Adults (Male and Female). This relative of Heterobilharzia americana is a parasite of humans.

Schistosoma mansoni

The schistosome eggs lack an operculum. The egg of Heterobilharzia americana does not have a spine like the one seen on this egg.


Class Cestoda

Tapeworms of small animals

Diphyllobothrium latum: dog, cat, mink, seal, human - Freshwater fish life cycle

Spirometra mansonoides: cats - Frog or Watersnake life cycle

Mesocestoides: dog, cat - Arthropod/Vertebrate life cycle

Mesocestoides corti
Mesocestoides corti eggs
Mature Mesocestoides corti proglottid.
Note the paruterine organ (to the left in the photo). Gravid, "club-shaped" proglottids pass in the feces
Mesocestoides corti eggs
These eggs were expressed from a gravid proglottid. They measure 40 to 60 Ám in diameter.


Dipylidium caninum: dog, cat - Flea life cycle

Dipylidium caninum
Dipylidium caninum eggs
Dipylidium caninum
Adult worms may reach up to 50 cm in length.
Dipylidium caninum egg packets
Each egg packet contains up to 20 eggs and within each is an onchosphere bearing 3 pairs of hooks. The egg packets pass from the dog within the gravid proglottid, from which they must be expressed for identification.
  Dipylidium caninum proglottids on feline feces
At least 7 proglottids can be seen on this fecal specimen:
Four are near the kitty-litter and 3 others are to the right of the
These proglottids are usually noticed by the owner who will tell you they saw "rice grDipylidium caninum fecal sampleains" or tapeworms in the cat's stool. The segments may or may not be in the sample that is brought to you as the proglottids are motile.

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Taenia sp.: dog, cat - Small Mammal or Human/Livestock life cycle

Taenia saginata in situ
Taenia saginata
Taenia taeniaformis
Taenia saginata
Cysticerci in the heart of a cow.
Taenia saginata Cysticerci
that many of the protoscoleces have everted.
Taenia taeniaformis
Adult worms

Click here to link to a video of a live Taenia taeniaformis proglottid

Echinococcus granulosus: dog - Sheep life cycle

Echinococcus granulosus
Echinococcus granulosus stained
Echinococcus granulosus in situ
Echinococcus granulosus
Stained adult
Echinococcus granulosus

Adult Echinococcus granulosus
in situ (dog small intestine)

Echinococcus granulosus cysts
Echinococcus granulosus cysts
Echinococcus granulosus
Hydatid cysts in the liver of a sheep.
Echinococcus granulosus
Hydatid cysts being removed from the liver of a human.
Echinococcus granulosus cyst diagram
Diagram of a hydatid cyst.
Echinococcus granulosus cyst histology
Cross section of a hydatid cyst. Host tissue can be seen in the upper left corner, then the wall of the cyst, the germinal layer and finally a daughter cyst, containing protoscoleces, floating free in the fluid-filled interior.

Click here to link to the Echinococcus granulosus life cycle.


Tapeworms of large animals

Moniezia expansa: sheep - Mite life cycle

Moniezia expansa Moniezia expansa adult
The adult of this large tapeworm (up to 6 m) is found in the small intestine of sheep (esp. lambs).
The intermediate host is a free-living mite.

Moniezia expansa eggs

Moniezia expansa eggs
Triangular in shape, contain a "pyriform apparatus," and
measure approximately 56 to 67 Ám.


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Copyright © 2008 - University of Pennsylvania School of Veterinary Medicine, All rights reserved.
Faculty: Dr. Thomas Nolan
Students: Takis Weekes V'11, Molly Church V'09, Diana Knight V'08, Douglas Gilson V'05, Chris Dykhouse V'04, Kimberly Mah V'00

Comments or Questions contact Dr. Tom Nolan at: