Helminths :- Type study- Fasciola hepatica or liver fluke

 

Habit and Habitat of liver fluke –

Living fluke or Fasciola hepatica is digenetic trematode which is found in the bile passage and liver of sheep and other domesticated animals. It complete its life cycle in snail (pila). It enjoys a worldwide distribution. As this animal completes its life cycle in two hosts, Hence it is called as digenetic.

Internal organization

• Body wall – Body wall of Fasciola or liver fluke is characteristics and adapted for parasitic of life. It has no cellular epidermis and consists of the following layer :-
• Outer layer is thick and homogenous, formed of cuticle. It is made up of scloroproteins and bears many spines over it.
• Below the cuticle a thin basement membrane is present.
• Below the basement membrane, a sub- cuticular muscle layer is present. It is of three layers :-

a.       Outer layer of circular muscles.

b.       Middle layer of longitudinal muscles.

c.       Inner layer is called diagonal muscle layer.

• Parenchyma or Mesenchyma :- The interior of the body, between the organs is occupied by large number of branching, fluid filled parenchymatous cells.
• Gland cells :-  Many unicellular gland cells are found embedded in the muscular layer is called as gland cells .

Digestive organs

In Fasciola the digestive system is complex and digestive organs are branched. It bears mouth but anus is absent.

Digestive organs consists of the following parts:-

a.       Mouth – It is a small opening, situated ventrally at the apex of head lobe. Mouth is surrounded by oral sucker.

b.       Oral chamber – Mouth opens behind into a short, funnel shaped oral chamber.

c.       Pharynx – Pharynx is short rounded and muscular thick wall tube. Oral chamber leads into pharynx. It bears pharyngeal glands.

d.       Esophagus – Esophagus is a short, narrow structure opens behind into the intestine. Pharynx opens into esophagus posteriorly.

e.       Intestine – Intestine of Fasciola is divisible into lateral - 2 branches. Each lateral branch is branched and running on either side of the body up to the posterior end. Posterior part of intestine is closed. A large number of caeca or diverticula an given out along either side of the whole length of the intestine. The diverticula of outer side is highly branched and large. But the diverticula of inner side are short and unbranched.

Excretory system

The excretory system of Fasciola is consists of-  

1. Branched excretory duct.
2. Gland cells
3. Excretory duct

• There is a control or main excretory canal found in the body of Fasciola. Excretory canal is running medially for about 3/4^th of body length posteriorly. It opens outside through an excretory pore. Excretory pore is present mid ventrally at the posterior end of the body.
• From the main excretory -2 Antro-dorsal excretory ducts and 2- Antro- ventral duct arises. Antro-dorsal excretory ducts of Antro-ventral ducts gives off numerous branches on their sides. These side branches organ gives many minute branches is called capillaries. The end of minute capillaries forms flame cells.

The flame cells :-

• Each flame cells is present at the tip of the excretory duct. Each flame cell is an irregular mesenchyme cell with thin elastic cell wall, peripheral cytoplasm and a central intra cellular space.
• A bunch of long vibratile cilia flickers constantly like a flame inside the central space. By the flicking (vibration) of the cilia drives the parenchyma and pour into the excretory ducts. Waste products passes through the other excretory duct of reaches finally to the central excretory canal. As central excretory canal opens out side by excretory pore, waste materials are expelled out side the body of Fasciola.

Respiratory system

• The respiratory organs are absent because it selves inside the body, hence the respiration in anaerobic type (i.e respiration occurring in the absence of oxygen).
• It is completed by the fermentation of glycogen. Glycogen breaks into CO₂ and fatty acids of liberates energy.

Nervous system

Nervous system is well developed consists of :-

• A pair of cerebral ganglia.
• A nerve collar around the esophagus and connective the cerebral ganglia.
• Nerves from the cerebral ganglia to the head lobe and to the hinder part of the body.
• A pair of thick lateral nerves extending to the posterior end of the body and a pair of their dorsal and ventral nerves to the various organs of the viscera of the body.

Reproductive system

Fasciola hepatica are mostly hermaphrodite i.e; male and female reproductive organs are present in the same individual.

Male Reproductive organs :-

a.       Testes :- One pair of highly branched testes present. It is tubular. One testes lying behind other in the posterior middle part of body.

b.       A pair of vasa-deferentia:-  From each testes a narrow duct arises is called vasa-deferentia. The two vasa-deferentia runs forward and meet to form a common sperm duct and lying below ventral sucker.

c.       Seminal vesicle:- It is a pear shaped structure lying inside the cirrus sac. The common sperm duct dilates to form seminal vesicle.

d.       Ejaculatory duct:- It is a fine convoluted tube arises from the seminal vesicle. Ejaculatory duct runs forward through the cirrus and open into genital chamber through male genital pore.

e.       Cirrus and cirrus sac:- Cirrus or penis is a muscular structure. It can everted and drawn in through the genital pore. It helps in copulation.

The cirrus and the seminal vesicle both are enclosed in a bag like cirrus sac.

f.        Prostate gland:- Numerous unicellular prostrate glands are found around the ejaculatory duct.

Female Reproductive Organs :-

The following organs are included under female reproductive system :-

• .       Ovary :- There are single ovary in Fasciola. Ovary is large, tubules and highly branched. It is situated on the right side in front of testes.
• .       Oviduct :- Oviduct is short . It arises from the inner side of ovary. It runs down wards and back wards, to join uterus. During this course it gives laucers canal.
• .       Vitelline gland and vitelline duct:- Numerous minute vesicles like structures are found on lateral side of the body. These are called as vitelline glands. A fine duct arises from each vesicle and after uniting with similar ducts from other vesicles opens into the lateral longitudinal duct. The two longitudinal ducts are connected in the middle line by transverse vitelline duct. A median duct arises from the transverse vitelline duct and joins the oviduct.
• .       Laucers canal :- Laucers canal arises from the oviduct and acts as sperm duct. It opens outside during breading seasons.
• .       Ootype :- The place of union of oviduct and vitelline duct becomes swollen. It is called ootype. Inside the ootype eggs are collected.
• .       Shell gland or Mehlis glands:- Many unicellular glands are surrounding the ootype is called shell gland. The Secretion of shell glands secretes the shell around the eggs. The secretion makes the passage of uterus smooth.
• .       Uterus :- Uterus arises from ootype as a wide tube. Uterus runs forwards and opens into genital atrium. It opens on the left side as female genital aperture. It is filled with fertilized eggs. The terminal part of the uterus are muscular.   

• 

  Reproductive System of Fasciola hepatica