Biological Sciences 318- Parasitology Lab

Platyhelminthes - Cestodes

Kingdom: Animalia

(unranked): Protostomia

(unranked): Spiralia

(unranked): Platyzoa

Phylum:

Platyhelminthes

Characteristics:

1) simplest bilaterally symmetrical animals

2) 3 layers fundamental cell layers (ectoderm, endoderm, mesoderm)

3) body contains no internal cavity

4) dorsoventrally flattened (diffusion)

5) some possess a blind gut (i.e. it has a mouth but no anus)

6) protonephridial excretory organs (flame cell)

7) elaborate nervous system (allows for invasion of a variety of habitats)

8) reproduction mostly sexual as hermaphrodites

9) inability to synthesize fatty acids and sterols (commensals or parasites)

• all endoparasitic (nearly every species of vertebrate)

• no mouth, no digestive system (only vestigal sucker and pharynx remaining)

• large reproductive system!

• absorb nutrients through tegument

CestodaTapeworms

EucestodaTrue tapeworms

Form and Function: a. Scolex with holdfast organelles (suckers, grooves, hooks, spines)

- 3 types of sucking depressions:

i- Bothria: shallow sucking grooves (Pseudophyllidea)

ii- Bothridia: 4 leaflike flexible structures (Tetraphyllidea)

iii- True suckers/acetabula (Cyclophyllidea)

b. Neck

c. Strobila (divided into proglottids)

Strobilation: Addition of new proglottids in neck region

Mature from AP

Apolysis: gravid proglottid breaks off releasing eggs

Alternatively eggs released through uterine pore.

EucestodaTrue tapeworms

Form and Function: Reproductive Systems

Order: Cyclophyllidae (Taenia spp.); Pseudophyllidae (Diphyllobothrium latum)

EucestodaTrue tapeworms

EucestodaTrue tapeworms

Order: Pseudophyllidae• bothriate scolex (possessing dorsal and ventral groove = bothrium)• Testes and vitellaria scattered throughout the proglottid• The ovary is bilobed and posterior. Genital pores ventral • An uterine pore present on dorsal or ventral surface• Eggs are operculate and contain ciliated embryo, the coracidium • Adult parasites of all classes of vertebrates, but fish are their primary host. • The life cycle involves procercoid (larval stage often found in copepods) and plerocercoid larval stage (found in fish) 

Diphyllobothrium latum (broad fish tapeworm) Can be a serious pathogen, causing a pernicious anemia in human due to the worm absorbing large amounts of vitamin B12

EucestodaTrue tapeworms

Order: Cyclophyllidea

• scolex that usually contains four suckers; rostellum is present or absent (may be armed)

• The genital pore is usually lateral; Vitelline gland is single, compact, and posterior to the ovary.

• Eggs develop into some form of bladderworm in invertebrate or vertebrate intermediate host.

• Common tapeworms of birds and mammals, although some are found in reptiles.

• Infective eggs contain an oncosphere larva that bears 6 hooks.

• Variety of intermediate host types, both invertebrate and vertebrate

P

A

EucestodaTrue tapeworms

Order: Cyclophyllidea

• Depending on cestode species: larval stage in the vertebrate intermediate host the

Metacestode: cysticercus, strobilocercus, coenurus (multiceps), hydatid or cysticercoid.

• Family Taeniidae, Genus Echinococcus, Family Dilepididae, Hymenolepididae, Anoplocephalidae

Echinococcus granulosus

Taenia pisiformis

Diphyllobothrium latum

Hymenolepis diminuta cysterceroid life stage

Taenia egg

Diphyllobothriumltaum eggs

Hymenolepis diminuta egg

Echinococcus granulosus hyatid cysts multilocular cyst

Dipylidium caninum

Review SessionFri. Feb 6 1:00 – 4:00

Mon. Feb. 16 2:00-5:00

Lab Exam Feb 17-19

(date varies by lab section)

Learning Objectives1. Platyhelmintes - Flatworms-Why are they flat? Why are they special?-Know that reproductive structures are used in id!2. Subclass Eucestoda-Polyzoic; body parts; Strobilation-Hermaphrodites or monoecious; compare eggs-Difference between Cyclo- & Pseudophyllidae3. Order Cyclophyllidae-General characteristics4. Family Taeniidae-General charcterristics5. Genus Taenia-Life cycle, hosts, stages, transmission, etc.-Taenia pisiformis (scolex, immature, mature, gravid proglottid)-Anatomy of mature proglottid-Taenia eggs: non-operculate, radial lines (striated appearance), thick-shelled-Cysticercus: cross section + whole mount; invaginated scolex;6. Genus Echinococcus-Echinococcus granulosus-Life cycle, host, transmission, pathology-Visual id-Tissue section: unilocular cyst, brood caspules, protoscolices-Hydatid sand: protoscolices-Echinococcus multilocularis: multilocular cyst (Why worse?)7. Family Dilepididae-General characteristics8. Dipylidium caninum-Life cycle, hosts, transmission, etc.-Double-pored tapeworm!-Double reproductive system, egg capsules containing many eggs, scolex9. Family Hymenolepididae-Life cycle-Cysticercoid slide in invertebrate Hydra host-Eggs10. Order Pseudophyllidae-General characteristics11. Diphyllobothrium latum-Life cycle, transmission, host, stages, etc.-Pathology-Scolex: bothria-Eggs: operculate, contain ciliated embryo (coracidium)

VocabularyMonoeciousDioeciousEndoparasiticPolyzoicScolexStrobilaProglottidsOperculumCoracidiumStrobillationMetacestodeCysticercusCoenurusHydatid cyst and sandCysticercoidEvaginationBothriaVitellariaGravidBrood capsulesUnilocular cystMultilocular cystProtoscolexProcercoidPlerocercoid