introduction to trematodes

Introduction to the Helminths

Although the Protozoans are an extremely successful group, their organizational plan is limited due to their small size.

Limit in size has been escaped through:

1. _____________________________________________

2. ________________________________________________________________________________________________

The ________________________________ contains some _________________ and includes a number of parasitic organisms.

The first group of parasitic animals we will examine are the HELMINTHS – ________________________________ 

Helminth Phyla

Phylum _____________________________ -

Phylum _____________________________ -

Phylum _____________________________ - (of little economic importance – we will not study them)

______________________________ - study of parasitic worms.

Phylum Platyhelminthes – Chapter 13

The flatworms are the planarians, trematodes, and tapeworms.

Forms present in the phylum?

____________________________________________

____________________________________________

____________________________________________

Phylum Platyhelminthes – Chapter 13

Characteristics of the Phylum Platyhelminthes:1.

2.

3.

4.

Characteristics of the Phylum Platyhelminthes cont.

5.

• first animal group to have this system

• Function?

6.

Characteristics of the Phylum Platyhelminthes cont.

7. ________________________________________ ________________________________________

- absent in the tapeworms

8. _______________________________________

_______________________________________

- limits size so most flatworms are small and soft-bodied.

9. ________________________________________

- most flatworms are _________________

- both male and female organs occur in an individual

Taxonomy of the Phylum Platyhelminthes

We will use the traditional taxonomy:

Phylum Platyhelminthes

Class Turbellaria – planarians

Class Monogenea – monogenetic flukes

Class Trematoda – digenetic flukes

Class Cestoidea – tapeworms

As in the Protozoa, a new taxonomic scheme has been proposed which divides the Turbellaria into several taxa. However, we will not use the new scheme and use the traditional taxonomy.

Class Turbellaria

Most turbellarians are free-living scavengers, but some are ___________________________ on other invertebrates.

Characteristics of the Turbellaria:

1. _____________________________________________________

- Epidermis is _______________________on the ventral surface to aid in locomotion

Class Turbellaria

2. Anterior end:

3. Digestive tract:

• One anterior and 2 posterior branches

• No anus – all wastes have to leave via the mouth

Characteristics of the Turbellaria cont.:

4. ____________________________ ____________________________are present but do not stain in whole mounts

5. ____________________________

larval stages?

Representative Turbellaria

Dugesia – freshwater planarian

It is a free-living scavenger.

Bdelloura – commensal on the __________________________

Class Monogenea

All members of the Monogenea are parasitic

• most are ____________________________________________

• a few species occur _____________________________________________________

• one species in the hippopotamus eye

Characteristics of the Class Monogenea1. Characteristic structure is the

_______________________

- posterior attachment structure consisting of suckers &/or hooks

- function?

2. Anterior feeding and attachment structure is the _______________________ that contains the mouth

Characteristics of the Class Monogenea

3. Digestive tract consists of:

Characteristics of the Class Monogenea

3. Monogeneans are monoecious but cross-fertilize

• Male reproductive system consists of _______________ ________________________

•  Female reproductive system consists of:

________________________ – produces oocytes

________________________ scattered throughout the body – produces eggshell protein

________________________– contains 1- few eggs

4. Pathology

____________________________

Characteristics of the Class Monogenea

5. Life cycle is a direct cycle involving one host.

Adult on fish gill or in Egg shed into water urinary bladder of frog or turtle

  hatches

  attaches to host

Free swimming ____________________________

- ciliated - opisthaptor distinct - 2 eyespots - digestive tract & protonephridia present

2 members of Class Monogenea

Polystomoidella – parasite in the urinary bladder of the snapping turtle

Microcotyle – parasite on the gills of the sheepshead fish.

Note numerous clamplike structure on the opisthaptor.

Class Trematoda

Trematodes are __________________________________ in all classes of vertebrates.

These worms have become structurally adapted for a parasitic existance:

1. possess ___________________for attachment to host

  2. have many types of ____________________to produce secretions for ___________________________________ or to produce a ___________________________

3. have high _________________________(reproductive capacity) to increase chances of completing complex life cycles

Subclasses of the Class Trematoda

Of the 3 subclasses in the Class Trematoda, we will examine 2 of them:

Subclass Aspidobothrea (= Aspidogastrea)

Subclass Digenea

Subclass Aspidobothrea

Most are parasites in the viscera of ____________________

A few are parasitic in the intestines of ________________________________________________

Cotylogaster - a parasite in the small intestine of the sheepshead fish- is a representative of this subclass. 

Subclass Aspidobothrea - Cotylogaster

Characteristic structure is ______________________ composed of numerous shallow depressions called ____________________

(this sucker resembles bottom of tennis shoe)

Subclass Aspidobothrea - Cotylogaster

Digestive tract consists of:

Subclass Aspidobothrea - Cotylogaster

Adults are monoecious:

Male and female reproductive organs are similar to those of digenetic trematodes (I will discuss these shortly)

Importance?

Life cycle of Cotylogaster

Life Cycle – Addition of fish host:

Adult in fish intestine

clam eaten by fish

Adult in clam viscera egg released into water

hatches

enters clam via free-swimming _______________________ incurrent siphon

- has tufts of cilia - eyespots - long unbranched intestine

Subclass Digenea

Most abundant subclass - contains the digenetic trematodes

All are _________________________ in all classes of vertebrates

• inhabit many vertebrate organs (not limited to the intestine)

• many species infect humans and domestic animals and are of medical and veterinary importance

Subclass DigeneaLife cycles are complex involving at least 2 hosts - term "digenea" means 2 beginnings representing the 2 hosts

• first intermediate host is a ______________________________

• definitive host is a ________________________________ 

• many life cycles have a third host between the snail and vertebrate - the second intermediate host - this is an __________________________ ___________________________________________________________

Many larval stages occur in the intermediate host(s) - _____________________________________occurs in some of the larval stages Adults occur in the definitive host - ___________________________________ occurs in this host

Morphology of an Adult Digenetic Trematode

Size -

Characteristic structures are the 2 suckers

1. _____________________________ - at anterior end surrounding mouth - for attachment and feeding

2. _____________________________ (= ventral sucker) - located midventral to oral sucker - no internal opening - for attachment to host

Suckers are strongly muscularized consisting of bands of smooth muscle

Taxonomic importance -

Body wall is a tegument

It consists of 2 layers:

1. Syntegument

- outer ____________________ ____________________layer

- contains mitochondria, secretory bodies, and occasional spines

- a chemical layer called the ___________________ lies on top of outer cell membrane

syntegument

Tegument

2. Cytotegument

- cell bodies or ___________________ beneath the syntegument

- each cell contains a nucleus and organelles (RER & Golgi)

- involved in production of ____________________

- separated from syntegument by layers of tegumental muscle

- connected to syntegument by cytoplasmic bridges

syntegument

cytotegument

Tegument

syntegument

cytotegument

cyton

Tegument

Functions of the Tegument:

(1)protects trematode from ____________________________

(2)protects trematode from _____________________________

(3) absorbs ______________________________________for trematode nutrition

Trematode Digestive Tract

___________________________ is contained in oral sucker

Muscular ___________________ creates sucking action

Short esophagus leads into 2 long blind-ending _________________ (= intestinal ceca)

No anus so ______________________________________________________

Digestion and the Parenchyma

Food taken into the digestive tract consists of ______________________________

______________________________

Proteins are digested in the lumen of the intestine and _______________________________are absorbed through the intestinal epithelium.

Parenchyma

PARENCHYMA- loosely arranged cells filling space between internal organs.

Major function is:

Trematode Excretory System

EXCRETORY SYSTEM removes excess water that has diffused into worm

_______________________________ _______________________________ occur throughout the body

-cells contain beating flagella that create a hydrostatic pressure which draws water from the parenchyma into the collecting duct

- flame cells are seen only _______________________________

- at the posterior end of the worm:

Trematode Nervous System

Ladder-type system consisting of anterior ganglionic mass, lateral nerve trunks, and connecting commissures.

Sense organs of adults are at the cellular level within the tegument - ______________________________________________________________

Sense organs of free-swimming larval stages (miracidium & cercaria) are well developed: ______________________________________________________________

Trematode Reproductive Systems

Reproductive systems are extremely elaborate and specialized

Digenetic trematodes have ___________________________ - some produce as many as 25,000 eggs per day.

Most digenetic trematodes are _________________________

- schistosomes are only dioecious group

- monoecious forms commonly cross-fertilize but self-fertilization is possible

Male reproductive systemTwo testes – function?

Male reproductive systemTrematode sperm are unusual for 2 reasons:

1. ________________________________________________________

2. ________________________________________________________

nucleus 2 flagella mitochondrion

Male reproductive systemShape and position of the 2 testes are important taxonomic characters

 Shape: Position:

Combination of shape/position: branched tandem testes; lobed opposite testes, etc.

Male reproductive systemSperm ducts consist of 2 ____________________________ which join to form a single _______________________

Vas deferens leads into the cirrus sac (= cirrus pouch) that contains:

- ____________________________ - sperm-storage area

- _____________________________- produces fluids to maintain sperm

- _____________________________- male copulatory organ which can be everted through the ______________________________ for copulation

Female reproductive systemSingle ovary produces ___________________________ which pass along the oviduct to the ___________________________

Taxonomic importance?

Female reproductive systemShape and position of the ovary in relationship to testes important in identification 

 Shape:

oval

lobed

branched

Female reproductive systemOotype is region of female system where:

(1) ____________________________

(2) ____________________________

Female reproductive systemStructures associated with the ootype:

1. ________________________ - sperm storage area of the female system

2. _________________________ is a short duct which leads from the seminal receptacle to the outside.

• Laurer's canal was once a vagina but has lost this function and now serves to ________________________________________________

Female reproductive systemVitellaria (= vitelline glands)

- occur in _____________________ which generally stain intensely

 - secrete ______________________ which will coalesce in the ootype to form the _______________________

- vitelline cells containing this protein pass along vitelline ducts which join and lead into the ootype

Female reproductive system

Mehlis' gland - surrounds the ootype

 - produces secretions that ______________________________ ______________________________in the ootype

- stains a light pink

Female reproductive system___________________________

leaves from the ootype and consists of a long, often highly coiled duct containing eggs and sperm

As the eggs pass through the uterus, 2 processes occur:

1.

2.

Uterus function -

Female reproductive system Anteriorly, the uterus leads into a

strongly muscularized duct called the __________________________

  - this functions as an ovijector, forcing eggs out the common genital pore

  - metraterm joins the cirrus sac at the __________________________

Trematode Anatomy – Representives

We will examine the anatomy of Prosthogonimus macrorchis, the chicken and duck oviduct fluke, in lab.

Trematode Anatomy – Representatives

We will examine the anatomy of Quinqueserialis, the muskrat cecal fluke, in lab.

Trematode Anatomy – Representatives

We will also examine the anatomy of the immature adult of Leucochloridiomorpha from a snail. We’ll examine living specimens to see excretory system and beating of the protonephridia. We will compare living specimen to stained whole mount.