lecture 6 Flashcards
what group of organisms is the class trematoda?
digenetic flukes
trematodes are commonly referred to as ____
flukes
why are digenetic flukes, digenetic?
their life cycle involves two hosts, meaning their are two beginnings
what is the first intermediate host of digenetic trematodes?
almost always a mollusk (usually a snail)
what is the definitive host of a digenetic trematode?
a vertebrate
many ____ stages occur in the intermediate host
larval
___ trematodes are found in the definitive host
adult
all trematodes are obligate ___ parasites in all classes of vertebrates
endo
what parts of the host do digenetic trematodes infect?
the blood vessels, GI tract, lungs, or liver
what are the larval stages of the digenetic trematode?
- egg
- miracidium
- sporocyst
- redia
- cercaria
- metacercaria
- adult flukes
what are the characteristics of the adult digenetic trematode?
the 2 suckers:
- oral sucker - at anterior end surrounding mouth - for attachment and feeding
- acetabulum - a.k.a the ventral sucker - located mid-ventrally to oral sucker; no internal opening; for attachment to host
suckers are strongly muscularized consisting of bands of ___ ___
smooth muscle
asexual reproduction/larval stages occur in the ___ host
first intermediate
the adult digenetic trematode’s body wall is a ____
tegument
what are the two layers of the digenetic trematode’s tegument?
- syntegument
2. cytotegument
what is the syntegument?
- 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
what is the cytotegument?
- 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
what are the functions of the tegument?
- osmoregulation
- synthesis and secretion of mucus (to protect against host enzymes)
- absorption of nutrients for trematode nutrition
what are the characteristics of the trematode digestive tract?
- 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
what is the parenchyma?
loosely arranged cells filling space between internal organs
what does the excretory system do?
removes excess water that has diffused into the worm
what are flame cells?
cells that contain beating flagella that create a hydrostatic pressure which draws water from the parenchyma into the collecting duct
where are the flame cells located in the adult digenetic trematode?
at the posterior end of the worm is an excretory bladder
what does the digenetic trematode’s nervous system consist of?
the ladder type-system and sense organs
what does the ladder-type system consist of?
anterior ganglionic mass, lateral nerve trunks, and connecting commissures
where are the sense organs located in adult digenetic trematodes?
at the cellular level within the tegument
sense organs of ______ stages are well developed
free-swimming larval
reproductive systems are extremely ___ and ____
elaborate
specialized
almost all digenetic trematodes are ______ with one exception: ____
hermaphroditic
schistosoma spp
trematodes ____ in three possible ways
reproduce
what are the three possible ways of reproduction in trematodes?
- auto-fertilization
- cross-fertilization
- living together as a long-term unit, with the larger male surrounding the smaller, thinner female worm
what does the male reproductive system consist of in the adult digenetic trematode?
- two testes
- sperm ducts - consist of 2 vas efferentia which join to form a single vas deferens
- vas deferens - leads into the cirrus sac
____ and ___ of the 2 testes are important taxonomic characters
shape
position
what does the female reproductive system consist of in the digenetic trematode?
a single ovary that produces eggs which pass along the oviduct to the ootype
shape and position of the ovary in relation to the testes is important in ____
identification
what is the morphology of the digenetic trematode egg?
well developed eggshells enclosing the ovum, one or more sperm cells, and a number of vitelline cells
the digenetic trematode egg is usually ____
operculate
what is the difference in egg morphology between trematodes and schistosomes?
schistosome eggs are non-operculate and are ornamented with spines
following fertilization, an embryo or _____ develops
miracidium
the hatching eggs involves the release of the _____
opercular cap (if present)
what are the important factors involved in the eggs hatching in the external environment?
light, temperature and changes in the osmotic pressure
in all cases the egg hatches to release the ____
miracidium (usually the free-swimming form)
what is the miracidium?
- the ciliated (in most but not all cases) larval stage that is hatched from the egg
in most cases the miracidium is usually a free-swimming stage that seeks out the primary, and in some cases, _____ host of these parasites
intermediate
what happens in the case where the miracidium is not a free swimming stage?
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
different species of trematode will undergo different patterns of larval development, although the ____ will ____ develop into a sporocyst to start with
miracidum
always
the miracidium metapmorphoses to the ___ ___ stage through the loss of ciliated cells, the penetration glands, and the apical gland
early sporocyst
in some cases, the sporocyst develops within the ____ host as a hollow fluid filled germinal sac containing germ cells into ___ ____
molluskan
mother sporocysts
germ cells multiply and develop internally into ___ ____, which are essentially the same as their parent sporocysts
daughter sporocysts
if daughter sporocysts are formed, the second larval stage, the ___, do not develop
redia
the redia stage is ___ in the schistosomes
absent
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
asexual division
miracidium
hundreds of thousands
what larval stage are the redia considered?
the 2nd stage
what host do the redia develop in?
the molluscan host (but absent in some groups, such as schistosomes)
redia differ from the sporocyst in that they are much more ___ and possess a ____ gut
active
simple
the gut consists of a mouth that opens into a large muscular ____, which in turn opens into a ___ ___
pharynx
simple intestine
externally, behind the mouth, many redia have a ___ -___ ___, below which the birth canal opens and from which either ____ or ____ ____ emerge
ridge like collar
cercariae
daughter redia
what life stage of the trematode is the infective for the vertebrate host or plant?
the cercarial stage
what is unique about the trematode cercaria?
exhibit considerable variations in structure, which is very important taxonomically
the cercariae lead a brief free-living existence until a suitable _____ or place of encystment can be found
second intermediate host
some cercariae _____ the definitive host directly or the cercariae might be ____ by the definitive host
penetrate
eaten
what occurs in the case that the parasite employs three intermediate hosts?
the cercariae penetrate the second intermediate host to form a resting stage, the mesocercaria
what are the possible final intermediate hosts?
- a fish
- an arthropod, or
- another mollusk
