PHYLUM- PLATYHELMINTHES
characteristics of platyhelminthes
Platyhelminthes are more complexly designed than the earlier group.
They are bilaterally symmetrical.
They are triploblastic and acoelomate animals with organ level of organisation.
They flattened the body, hence are called flatworms.
These are mostly endoparasites found in animals including human beings.
Hooks and suckers are present in the parasitic forms.
Some of them absorb nutrients from the host directly through their body surface.
Specialised cells called flame cells help in osmoregulation and excretion.
Saxes are not separate.
Fertilisation is internal and development is through many larval stages.
Some members like planaria possess high regeneration capacity.
The circulatory system is undeveloped.
Examples : Taenia (Tapeworm), Fasciola (Liver fluke)
Classification
The phylum platyhelminthes is divided into three classes :
Turbellaria
Trematode
Cestode
Class 1. Turbellaria :-
The turbellarians are mostly free living. They are commonly called planarians.
Body is leaf -like and covered by a delicate, partly or fully ciliated epidermis.
Alimentary canal is usually present.
Mouth is often ventral.
Reproduction is both asexual and sexual.
Power of regeneration is well marked.
Example : Dugesia - the planarian.
Class 2. Trematoda.
The Trematoda have the following characters :
The trematodes are parasitic flatworms. They are commonly called the flukes.
Body is leaf -like and covered by a thick, living tegument. There is no epidermis.
Alimentary canal is present.
Mouth is anterior.
Life history often includes larval forms and involves more than one host.
They have suckers for attachment in the host.
Examples : Fasciola - the liver fluke
class 3. Cestoda
The cestoda have following characters :
The cestodes are intestinal parasites. They are commonly called tapeworms
Body is ribbon - like and covered by a thick,syncytial, living tegument. Tegument is bounded on both sides by plasma membranes and contains mitochondria. It takes up nutrients by active transport, and also evades the host 's immune reaction. There is no epidermis.
Body is divided into scolex, neck and strobila of a few to numerous proglottids. The latter are not true segments.
Alimentary canal and mouth are absent.
Life history involves two or more hosts and includes larva stages.
Scolex has suckers and hooks in many cestodes for attachment in the host.
Each proglottis has one or two sets of male and female reproductive organs.
Example : Taenia solium - the tapeworms.
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PHYLUM - ASCHELMINTHES
GENERAL CHARACTERISTIC
The phylum Aschelminthes include the roundworms. They possess the following characters :
1.Body form:- The body is cylindrical, tapering at both ends.It is without segmentation.
2. Symmetry :- The symmetry is bilateral in roundworms.
3. Germlayers :- The round worms are triploblastic.
4. Head :- Anterior end doesn't form a distinct head.
5. Level of organisation :- The roundworms have an organ system of organisation.
6. Appendages :- There are no locomotory appendages in roundworms.
7. Body cavity :-A cavity is present between the body wall and the
Digestive Tract It is not lined by mesothelium. Therefore it is called pseudocoelom instead of coelom. It contains pseudocoelomic fluid.
8. Skeleton :- There is no mineralized skeleton. High fluid pressure in the pseudocoelom maintains body shape.It is called hydroskeleton.
9. Digestive Tract :- There is straight, one-way digestive tract with mouth as well as annus. Such a digestive tract is said to be complete. It allows food to move on without mixing successive meals and faeces to pass out of the annus.
https://kareenalohia232406.blogspot.com/2022/07/the-bases-of-human-behaviour.html10. Respiration :- Respiration occurs by diffusion through the body surface.
11. Circulatory system :-The circulatory system undeveloped.
12. Nervous system :- The nervous system is intraepidermal. It comprises a circumpharyngeal ring that sends nerves forward as well as backward. Sense organs (papillae, amphids) are present on the lips. Ampids are chemoreceptors.
13. Excretory system :- Excretory matter is mainly ammonia. An excretory tube removed body wastes from the body cavity.
14. Reproduction :- Saxes are generally separate. Sexual dimorphism is present. Male are smaller than females, their hind end is curved ventrally. Males genital tract joins the digestive tract to form a cloaca. Female genital tract opens out independently. Eggs are unbelievably numerous and resistant to environmental extremes. Fertilization is internal. There is no asexual reproduction. Development of eggs is direct.
Examples : Ascari - The giant intestinal roundworm
Enterobius - The pinworm,
Ancylostoma - the hookworm,
Wuchereria - the filarial worm
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