Parasitic adaptation may be defined as morphological,
physiological and behavioral modifications established by the organism to
survival a parasitic mode of life. Platyhelminthes also develop some adaptation
to cope with the environment (parasitic) they live. The followings are the
adaptation of the Platyhelminthes inside the hosts:
adaptations: Morphological adaptations can either be Loss of organs or
of new organs.
· Organs for locomotion:
Locomotion is generally required by the animal to procure food and shelter. But
parasite habitually inhabit such a place in the host’s body where there is no
need to make trip for food and safety. However, locomotory organs are present in the
free living tubellaria and free living larvae of the parasitic forms. For example,
the cercaria larva has a tail and miracidium larva of Fasciola possess cilia
system: Nervous system in Platyhelminthes is poorly advanced and has no sense
organs. Since nervous system is associated with free active life and not with a
quiet parasitic life in a safe environment lacking nervous system.
system: parasite feed on the digested or semi-digested food of the host, therefore
digestive system is absent. In class cestoda digestive system is absent or is
greatly simplified as in Flukes. Trematodes example Liver fluke have an
incomplete gut with a single opening, the mouth; anus is absent in them. There
is also a complete absence of digestive glands since the food is already in
digested state. Cestodes like tapeworm directly absorb the hosts digestive food
through the tegument and hence there is a total absence of the alimentary
Dorsoventrally flattened body. Flat and thin
body allows platyhelminthes to live in narrow spaces and also to obtain
nutrition food through diffusion.
for adhesion: Adhesive organs like suckers in Fasciola and hooks and suckers in
Taenia or spines are necessary because help the parasite to ?rm grip on or in
the host’s body.
covering: The tough, thick and resistant tegument is an important parasitic
adaptation. The tegument also provides protection against the action of
digestive juices of the host. The body covering is frequently provided with
scales and spines which give appropriate protection to the parasite. Fasciola
has a muscular and suctorial pharynx, modified to suck the hosts digestive
juices. It is possible that, this thick protoplasmic
layer is continually renewed by the cells developing it.
system: the internal parasites are characterized by having a complex
reproductive system designed and perfected to meet the need for the tremendous
egg production. In flatworms, the ovaries and testes are either greatly
enlarged or show an increase in number so that they are capable of producing a
large number of gametes. Almost all
parasitic platyhelminthes are monoecious except Schistosoma. Hermaphroditism is
of distinct advantage to the parasite as; It ensures copulation even when few
individuals are present, after copulation both individuals lay eggs, thus
doubling the rate of production. In the absence of another member of the same
species, the parasite can reproduce offspring by itself, like in Taenia. In event of the failure of cross
fertilization, they resort to self-fertilization in which close vicinity of the
cirrus and vulva is of great help. In cestodes, the reproductive system is much
more elaborate and each mature proglottid holds one or two sets of male and
female genetilia. In a gravid proglottid all other organs of the system
degenerate to make area for the highly branched uterus which becomes highly
enlarged and branched to accommodate a large number of eggs.
respiration: Platyhelminthes are
facultative anaerobes, can live in area where there is no oxygen content.
Environment in the gut and bile ducts is lacking of oxygen. The ?at-worms
inhabiting these places therefore, respire anaerobically by breaking down
The osmotic pressure of the endoparasite’s body ?uids, especially in case of
trematodes, is almost the same as that of the host therefore they do not need
to osmoregulation since they are well adapted to host osmoregulation. However,
in the intestinal tapeworm the osmotic pressure is a little higher this permits
ready absorption of host’s digested food by the parasite.
tolerance: the flatworms have high pH tolerance that make them capable to
survival in the place where there is high acid like digestive juices in the
human hosts stomach. The pH tolerance results because of the presence of the
hard cuticle in their body which helps them to do not get digested by the
mechanism: Parasites secrete anti- enzymes to neutralize the digestive enzymes
of the host. The alimentary canal parasites have to protect themselves from the
action of digestive juices of the host. The tapeworms accomplish this by
stimulating the walls of the gut to secrete mucus, which then forms a
protective coating around the parasite.
fertility: These parasites have a complicated life cycle; they require two or
more host to complete its life cycle. Eggs produced by a parasitic ?atworm face a
several hazards as a result of which a very small percentage of the total eggs
produced reaches adulthood. That why helminth produce a very large number of
eggs, such an enormous number of egg production is needed because the chances
of survival of the eggs are less. The reproductive organs of the ?atworms, as
already noted, are accordingly developed. Example several cercariae develop
from a single miracidium of liver ?uke. In flukes, a single egg produces
several embryos, a process called polyembryony. In them, the various larval
forms are produced by the simple asexual multiplication of germ cells thus a
single zygote gives rise to several adults.
capsule: Also eggs of helminths are covered by a resistant capsule or shell as
a result of which they can remain viable for a long time even in adverse
of several larval forms: Involvement of several larval forms in the life cycle guarantees
transmission of parasite from one host to another. Intermediate host ensures
wide spreading of the species. The availability of several hosts ensure the
survival of flatworms.
some platyhelminths (flatworms) are free-living and nondestructive, many other
species particularly the flukes and tapeworms parasitize infect domestic
animals or both. This occur when
sanitation is poor and meat eaten undercooked, the frequency of tapeworm
infestations is high. Example schistosomiasis or bilharziasis is a major human
disease caused by three species of the genus Schistosoma, known collectively as
blood flukes Parasites in immature stages, larvae can cause serious damage to
the host, many species are ingested as cysts. Thirty-six or more fluke species
have been reported as parasitic in humans. In humans these parasites and others
listed below cause much misery and death. These parasitic diseases are much
more found in Africa and western Asia.
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