lecture 6

Question 1

what group of organisms is the class trematoda?

Answer 1

digenetic flukes

Question 2

trematodes are commonly referred to as ____

Answer 2

flukes

Question 3

why are digenetic flukes, digenetic?

Answer 3

their life cycle involves two hosts, meaning their are two beginnings

Question 4

what is the first intermediate host of digenetic trematodes?

Answer 4

almost always a mollusk (usually a snail)

Question 5

what is the definitive host of a digenetic trematode?

Answer 5

a vertebrate

Question 6

many ____ stages occur in the intermediate host

Answer 6

larval

Question 7

___ trematodes are found in the definitive host

Answer 7

adult

Question 8

all trematodes are obligate ___ parasites in all classes of vertebrates

Answer 8

endo

Question 9

what parts of the host do digenetic trematodes infect?

Answer 9

the blood vessels, GI tract, lungs, or liver

Question 10

what are the larval stages of the digenetic trematode?

Answer 10

1. egg
2. miracidium
3. sporocyst
4. redia
5. cercaria
6. metacercaria
7. adult flukes

Question 11

what are the characteristics of the adult digenetic trematode?

Answer 11

the 2 suckers:

1. oral sucker - at anterior end surrounding mouth - for attachment and feeding
2. acetabulum - a.k.a the ventral sucker - located mid-ventrally to oral sucker; no internal opening; for attachment to host

Question 12

suckers are strongly muscularized consisting of bands of ___ ___

Answer 12

smooth muscle

Question 13

asexual reproduction/larval stages occur in the ___ host

Answer 13

first intermediate

Question 14

the adult digenetic trematode’s body wall is a ____

Answer 14

tegument

Question 15

what are the two layers of the digenetic trematode’s tegument?

Answer 15

1. syntegument

2. cytotegument

Question 16

what is the syntegument?

Answer 16

• it is the outer layer, contains mitochondria, secretory bodies, and occasional spines
• it is a chemical layer that lies on top of the outer cell membrane

Question 17

what is the cytotegument?

Answer 17

• cell bodies beneath the syntegument
• each cell contains a nucleus and organelles
• involved in production of mucus
• separated from syntegument by layers of tegumental muscle
• connected to syntegument by cytoplasmic bridges

Question 18

what are the functions of the tegument?

Answer 18

1. osmoregulation
2. synthesis and secretion of mucus (to protect against host enzymes)
3. absorption of nutrients for trematode nutrition

Question 19

what are the characteristics of the trematode digestive tract?

Answer 19

• muscular mouth creates sucking action
• short esophagus leads into 2 long blind-ending cecum (=intestinal ceca)
• no anus
• proteins are digested in the lumen of the intestine and are absorbed through the intestinal epithelium

Question 20

what is the parenchyma?

Answer 20

loosely arranged cells filling space between internal organs

Question 21

what does the excretory system do?

Answer 21

removes excess water that has diffused into the worm

Question 22

what are flame cells?

Answer 22

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

Question 23

where are the flame cells located in the adult digenetic trematode?

Answer 23

at the posterior end of the worm is an excretory bladder

Question 24

what does the digenetic trematode’s nervous system consist of?

Answer 24

the ladder type-system and sense organs

Question 25

what does the ladder-type system consist of?

Answer 25

anterior ganglionic mass, lateral nerve trunks, and connecting commissures

Question 26

where are the sense organs located in adult digenetic trematodes?

Answer 26

at the cellular level within the tegument

Question 27

sense organs of ______ stages are well developed

Answer 27

free-swimming larval

Question 28

reproductive systems are extremely ___ and ____

Answer 28

elaborate | specialized

Question 29

almost all digenetic trematodes are ______ with one exception: ____

Answer 29

hermaphroditic | schistosoma spp

Question 30

trematodes ____ in three possible ways

Answer 30

reproduce

Question 31

what are the three possible ways of reproduction in trematodes?

Answer 31

1. auto-fertilization 2. cross-fertilization 3. living together as a long-term unit, with the larger male surrounding the smaller, thinner female worm

Question 32

what does the male reproductive system consist of in the adult digenetic trematode?

Answer 32

1. two testes 2. sperm ducts - consist of 2 vas efferentia which join to form a single vas deferens 3. vas deferens - leads into the cirrus sac

Question 33

____ and ___ of the 2 testes are important taxonomic characters

Answer 33

shape | position

Question 34

what does the female reproductive system consist of in the digenetic trematode?

Answer 34

a single ovary that produces eggs which pass along the oviduct to the ootype

Question 35

shape and position of the ovary in relation to the testes is important in ____

Answer 35

identification

Question 36

what is the morphology of the digenetic trematode egg?

Answer 36

well developed eggshells enclosing the ovum, one or more sperm cells, and a number of vitelline cells

Question 37

the digenetic trematode egg is usually ____

Answer 37

operculate

Question 38

what is the difference in egg morphology between trematodes and schistosomes?

Answer 38

schistosome eggs are non-operculate and are ornamented with spines

Question 39

following fertilization, an embryo or _____ develops

Answer 39

miracidium

Question 40

the hatching eggs involves the release of the _____

Answer 40

opercular cap (if present)

Question 41

what are the important factors involved in the eggs hatching in the external environment?

Answer 41

light, temperature and changes in the osmotic pressure

Question 42

in all cases the egg hatches to release the ____

Answer 42

miracidium (usually the free-swimming form)

Question 43

what is the miracidium?

Answer 43

- the ciliated (in most but not all cases) larval stage that is hatched from the egg

Question 44

in most cases the miracidium is usually a free-swimming stage that seeks out the primary, and in some cases, _____ host of these parasites

Answer 44

intermediate

Question 45

what happens in the case where the miracidium is not a free swimming stage?

Answer 45

the eggs are ingested, and hatch in the intestine of the mollusk liberating the miracidium, from where it immediately penetrates the intestinal wall to invade the molluskan tissues

Question 46

different species of trematode will undergo different patterns of larval development, although the ____ will ____ develop into a sporocyst to start with

Answer 46

miracidum | always

Question 47

the miracidium metapmorphoses to the ___ ___ stage through the loss of ciliated cells, the penetration glands, and the apical gland

Answer 47

early sporocyst

Question 48

in some cases, the sporocyst develops within the ____ host as a hollow fluid filled germinal sac containing germ cells into ___ ____

Answer 48

molluskan | mother sporocysts

Question 49

germ cells multiply and develop internally into ___ ____, which are essentially the same as their parent sporocysts

Answer 49

daughter sporocysts

Question 50

if daughter sporocysts are formed, the second larval stage, the ___, do not develop

Answer 50

redia

Question 51

the redia stage is ___ in the schistosomes

Answer 51

absent

Question 52

the cycles of ___ ___ within the mollusc result in an enormous increase in the reproductive potential of these organisms, where a single ____ can give rise to many _______ of cercariae

Answer 52

asexual division miracidium hundreds of thousands

Question 53

what larval stage are the redia considered?

Answer 53

the 2nd stage

Question 54

what host do the redia develop in?

Answer 54

the molluscan host (but absent in some groups, such as schistosomes)

Question 55

redia differ from the sporocyst in that they are much more ___ and possess a ____ gut

Answer 55

active | simple

Question 56

the gut consists of a mouth that opens into a large muscular ____, which in turn opens into a ___ ___

Answer 56

pharynx | simple intestine

Question 57

externally, behind the mouth, many redia have a ___ -___ ___, below which the birth canal opens and from which either ____ or ____ ____ emerge

Answer 57

ridge like collar cercariae daughter redia

Question 58

what life stage of the trematode is the infective for the vertebrate host or plant?

Answer 58

the cercarial stage

Question 59

what is unique about the trematode cercaria?

Answer 59

exhibit considerable variations in structure, which is very important taxonomically

Question 60

the cercariae lead a brief free-living existence until a suitable _____ or place of encystment can be found

Answer 60

second intermediate host

Question 61

some cercariae _____ the definitive host directly or the cercariae might be ____ by the definitive host

Answer 61

penetrate | eaten

Question 62

what occurs in the case that the parasite employs three intermediate hosts?

Answer 62

the cercariae penetrate the second intermediate host to form a resting stage, the mesocercaria

Question 63

what are the possible final intermediate hosts?

Answer 63

1. a fish 2. an arthropod, or 3. another mollusk