Phylum Platyhelminihes, Biology tutorial

Introduction to Phylum Platyhelminihes:

Phylum Platyhelminthes symbolizes all flatworms in kingdom Animalia. Flatworms are comparatively primitive animals which signify the early lineage in kingdom. Unlike even more ancient phylum cnidaria, all flatworms of phylum Platyhelminthes are bilaterally symmetrical, having posterior, anterior, dorsal, and ventral end and 2 apparently equal lateral surfaces.

General Characteristic Features of the Phylum Platyhelminthes:

i) They do not have circulatory, respiratory or skeletal system

ii) Their body are dorsiventrally flattened; called as flatworms

iii) Nervous system are ladder-like, with simple sense organs

iv) They lack body cavity therefore known as Acoelomate

v) They have entire reproductive organs

vi) They are bilaterally symmetrical

vii) Digestive system is absent in some; and if present has only mouth but no anus

viii) Triploblastic animals - composed of 3 body layers

ix) They have proto-nephridial type of excretory system.

Classification of Platyheminthes:

Phylum platyhelminthes is categorized into 3 main classes. These are:

i) Turbellaria: mainly free-living and aquatic, having soft bodies and leaf like in form. Their body is covered with cilias, few are terrestrial and limited to humid areas and with only 1 opening to gut. For e.g. planaria, etc.

ii) Trematoda: They are parasitic; lacking cilia; cuticle covering leaf like body with one or more suckers. For e.g. faciola hepatica (also called as liver fluke) schistosoma, also called as blood fluke, etc.

iii) Cestoda: They are endoparasites (internal parasites), comprising no gut (digestive) system. There are parasites in digestive tracts of different vertebrates. They are Ribbon - like in form composed of several segments (proglottids) with the anterior scolex carrying suckers and hooks to hest tissues. When mature, every prolothic has complete set of reproductive organs of both sexes. For e.g. Tapeworms such as Taenia solium, Taenia saginata etc.

Fasciola Hepatica (Sheep Liver-Fluke):

Fasciola hepatica is the example of trematode parasite. It needs 2 hurts to complete its life-cycle - a vertebrate as primary hurt, and invertebrate animal as secondary hurt.


External Morphology:

i) Body is soft and Pinkish - brown in colour

ii) Lengthened and dorso - ventrally flattened (leaf-like)

iii) Appear to be oral in shape, estimating 1.8 - 3 cm in length and 0.4 - 1.5 cm in width.

iv) Broad and rounded at anterior end of body; and bluntly pointed at posterior end.

v) Anterior sucker acts as the auctorial organ for adhesion and ingestion.

vi) It has muscular bowel - such as ventral or posterior sucker which is for adhesion simply

vii) Body has the minute gonopore or genital aperture mid-ventrally that is little in fruit of posterior sucker.

viii) Anus is absent.


Adult Fasciola hepatica lives in liver and bile pardges of primary host that is sheep but it may happen in some other venlebrales like man, goat, rabbit, dog ox deer, elephant etc. The primary hurt may harbor up to 200 adults of liver fluke in its liver that unbequently may stop to function (vidyartlic etal, 2005) causing liver not disease. Immature life-stages of fluke happen in the mollusc, Limnea truncatula, that is secondary or intermediate hurt, or in detailed species of planorbis. Liver-fluke is world-wide in distribution in sheep and cattle raising areas infection of the fluke is also formed in man.

Structural Adaptation:

i) Body-wall of liver fluke is made up of only cuticle (and musculature) that covers body as thick and tough layer, proving protection to fluke against chemicals of hurt. Digestive System: it blood, sucks bite, lymph etc. as food in alimentary canal because of suctorial pharynx. Interlinary caecal distribute them to different parts of body.

ii) Excretory System: It includes prolonephridial kind of excretory system that is made of large number of excretory cells known as flame cell. Excretory substances gathered in human of flame cell are pushed in excretory capillaries and tubules because of vibration of cilia of flame cells.

iii) Respiratory System: It respires by general body surface.

iv) Reproduction System: It is the hermaphrodite. Male and female reproductive organs are present in same individual.

Parasitic Adaptation:

i) As they live well protected, with hunger well fulfilled without any requirement for change of position, there is no requirement of locomotory organ

ii) They attach themselves to gut wall or bile ducts by suckers and hooks or suckers alone. In intertive of host, they can absorb digested food through the soft skin

iii) Sense organs are not present in without any inconvenience as they live in perpetual darkness

iv) Secretes certain antizymes that counteract or neutralizes digestive juices of host to prevent being digested

v) Intestinal parasites stimulate intestinal will of host to produce huge amount of mucus that covers thick cuticle of parasite with protective envelope.

vi) Ostmotic pressure of parasite's body fluids is almost same as that of host, if not, resulting exchange of water would establish serious disturbances

vii) They are hermaphrodite, making sure that eggs and sperms reproduced in one and same individual Paedogenesis or multiplication by larval form by asexual means - this enhances probability of survival.

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