Download - Trematode Life Cycles
![Page 1: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/1.jpg)
Life Cycles of Digenetic Trematodes Chapter 15, p. 230-237
Digenetic trematodes use 2 or 3 hosts in their life cycles.
FIRST INTERMEDIATE HOST is always a ___________________________.
Reproduction ?
SECOND INTERMEDIATE HOST may occur in some life cycles. This host is an _____________________________________________________
Reproduction?
DEFINITIVE HOST is a _________________________________.
Reproduction?
![Page 2: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/2.jpg)
Life Cycles of Digenetic Trematodes
As many as _____________________________________________ have been recognized in digenetic trematode life cycles.
- Many variations occur - not all 6 larval stages may be present within a species.
- Life cycles have been difficult to elucidate due to all these larval stages.
Today I will discuss a generalized trematode life cycle.
We will examine the specific life cycle of each trematode of medical and veterinary importance when we get to each one in lecture and lab.
![Page 3: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/3.jpg)
Generalized Life Cycle
![Page 4: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/4.jpg)
Adult
ADULT occurs in the definitive host
Although most adults are _____________________________.
Method of fertilization?
Sexual reproduction involving gamete formation (oocytes and sperm) followed by fertilization results in the formation of thousands of fertilized eggs.
![Page 5: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/5.jpg)
Egg = Ovum
After fertilization and eggshell formation in the ootype, eggs move through the uterus.
As they move through the uterus, 2 processes occur:
1. ______________________________ - eggshell is hardened into a tough protein called ______________________ as the egg passes along the uterus.
- function?
![Page 6: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/6.jpg)
Egg = Ovum
2. ________________________________________- mitosis of the zygote to form the embryo.
- If the embryo is fully differentiated into a miracidium before the egg is released from the adult, an _________________________________is produced.
- If the embryo consists of a number of undifferentiated cells when the egg is released, an _________________________________is produced.
embryonated egg unembryonated egg
![Page 7: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/7.jpg)
Egg = Ovum
Eggs are ejected from the adult by the
_____________________________ through the common genital pore.
Eggs leave the definitive host via ___________________________________________ (depending on the species) and are generally deposited into an aquatic environment.
Hatching of the egg may occur:
1.
or
2.
Hatching of the egg involves the opening of an ______________________________
![Page 8: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/8.jpg)
Miracidium
Ciliated embryo that hatches from the egg
Miracidia that hatch in water:
In some species, the egg is ingested by the snail and the miracidium hatches within the snail:
![Page 9: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/9.jpg)
Miracidium
Morphology: Small, elongate organism covered by __________________________ At anterior end is the _________________________ that functions in contacting the snail intermediate host. The apical papilla contains openings from _____________________________________. When a snail is contacted, the penetration glands secrete enzymes to aid in embedding the miracidium within the snail's tissues. ___________________________ are common for photoreception. A mass of ______________________________ lies in the posterior end. These cells divide asexually to form the next larval generation.
![Page 10: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/10.jpg)
Miracidium
Upon entering a snail, the miracidium loses its cilia and transforms into a sac-like body called the __________________________________________
![Page 11: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/11.jpg)
Sporocyst
Upon entering a snail, the miracidium loses its cilia and transforms into a sac-like body called the MOTHER SPOROCYST.
Mother sporocysts occur in the snail at the site of penetration.
Mother sporocysts consist of a _______________________________ surrounding developing _______________________________
mouth or digestive tract?
![Page 12: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/12.jpg)
Sporocysts
In some digenetic trematodes, the germ cells in the mother sporocyst divide asexually to give rise to another generation of sporocysts called ________________________. Mother sporocyst bursts to release these daughter sporocysts.
In other trematodes, the germ cells of the mother sporocyst form a new larval stage called the ______________________________
![Page 13: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/13.jpg)
Redia
Mother rediae burst out of the mother sporocyst and migrate to the __________________________________________________________of the snail host.
hepatopancreas
![Page 14: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/14.jpg)
Redia
Each redia contains a __________________________ and short ___________________________
What do they feed on?
________________________ in the mother rediae may develop into a second generation of rediae called _____________________________or may develop into _____________________________.
![Page 15: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/15.jpg)
Cercaria
CERCARIAE leave the sporocyst or redia, migrate out of the snail, and become __________________________.
Morphology:
1. Cercarial body is an ______________________________
- oral sucker and acetabulum are present
- digestive tract is complete
- excretory system is developed
- many types of gland cells are present
- 2 eyespots are common
- no reproductive structures
Furcocercous cercaria
Microcercous cercaria
![Page 16: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/16.jpg)
Cercaria
2. _____________________________ used for swimming.
- may be unbranched with or without fins
- tail characteristics important in identification
Type of cercaria is based on characteristics of the body and tail. We will look at 3 types:
Furcocercous type – forked tail
Gymnocephalous type – straight tail
Microcercous type – short tail
Furcocercous cercaria
Microcercous cercaria
![Page 17: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/17.jpg)
Cercariae may: (1) penetrate the definitive host (schistosomes)
(2) penetrate a second intermediate host and encyst as metacercariae, or
(3) attach to aquatic vegetation and encyst as metacercariae.
![Page 18: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/18.jpg)
Metacercaria
METACERCARIA is formed as a cercaria loses its tail and encloses itself in a ________________________________
Cyst is formed by:
1.
2.
Metacercaria is an ______________________________
Reproductive organs may begin to form but eggs are never produced.
![Page 19: Trematode Life Cycles](https://reader034.vdocuments.us/reader034/viewer/2022050720/55508543b4c905235b8b49aa/html5/thumbnails/19.jpg)
Metacercaria
Metacercariae may occur within a second intermediate host or on aquatic vegetation. They are viable for weeks to years.
When the second intermediate host or aquatic vegetation containing metacercariae is eaten by a definitive host, the metacercaria _____________________________in the digestive tract and matures to the ____________________________.