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 

ANNELIDA- EXCERETORY SYSTEM OF LEECH

The excretory system of leech can be studied under the two headings-

1. Excretory organ
2. Process of excretion

Excretory organ-

Nephridia are the main excretory organ of leech. Nephridia are segmentally arranged from 6^th to 23^rd segment. Each has hollow, microscopic tubes arranged in pairs. There are 17 pairs nephridia are found in Leech.

These are of two types :-

1.  Pretesticular Nephridia - 6 pairs
2.  Testicular Nephridia- 11 Pairs

Pretesticular Nephridia :-

 This type of Nephridia are found from 6^th to 11^th segment. This type of nephridia has no connection with testis; hence called as pretesticular nephridia. Haemocoelomic ampullae and ciliated organs are absent in this type of nephridia. In other structures they are similar with testicular nephridia.

 Testicular Nephridia :-

Testicular Nephridia are found from 12^th to 22^nd segments. They are attached with testis sacs. This is called typical nephridia and 11 pairs in number. Each testicular nephridium is horse shoe shaped in outline. It consists of six parts-  

     1.Main lobe   2.Vesicle and vesicle duct   3.Apical lobe  4.Inner lobe   5.Initial lobe   6.Ciliated organ

Main lobe:-

It is exactly horse shoe proper. Main lobe of the nephridium lies between the caeca of two crops. It is the main parts of nephridium and divisible into.

• Long anterior part - Anterior limb
• Short posterior part - Posterior limb

The cells of main lobe, consists of glandular polyhedral cells. The cells are connected with small canaliculi. Canaliculi of main lobe opens into central canal.

Anterior limb opens into vesicle duct and posterior limb connected with apical lobe.

Vesicle and vesicle duct –

The anterior limb of the main lobe continuous to form a duct called vesicle duct. Vesicle duct bends posteriorly and opens into vesicle.

Vesicle is a large, oval, non-contractile, sac like structure. The wall is thin and inner lining is ciliated.

 A small thin tube arises from vesicle and opens outside ventrally through nephridiopore. Sphincter muscles are found around nephridiopore.

 Apical lobe –

Posterior limb of the main lobe proceeds forward and forms apical lobe. It is found below the crop. Apical lobe is thick, stout and bends. It appears like the head of walking stick. The cells of apical lobes are larger. Intracellular canals are found in it. This canal opens into central canal.

 Inner lobe –

 It is a short lobe called as incurrent lobe. It is found between anterior and posterior limb. Inner lobe is continued to the outer border of apical lobe up to middle. It joins with main lobe in posterior side.

Initial lobe –

It is associated with apical lobe. It is thin long transparent cord like structure. It surrounds the apical lobe. Initial lobe is formed of single row of hollow cells. The anterior end of this lobe is closed but the posterior end opens into main lobe. Anterior end is situated near perinephrostomial ampulla on testis.

Intra cellular canal is present in the initial lobe. Intra cellular canal gives rise to diverticula in each cell.

Ciliated organ –

Ciliated organs are peculiar structure, present in perinephrostomial ampulla. Ciliated organs are suspended from the wall of ampulla by 4-5 strands or trabeculae.

Ciliated organs are similar to the nephrostome of the typical nephridium. Ciliated organ is a modified compound structure, divides into two parts-  

1. Central reservoir – Spongy
2. Ciliated funnel

Reservoir- It is formed of connective tissue spongy central mass. It forms coelomic corpuscles. The wall of this is unicellular a perforated. This aperture opens into ciliated funnel.

Ciliated funnel – Each ciliated funnel is small earlobe like. Th margins are ciliated.

In embryonic stage, ciliated organs are attached with nephridium but in adult Hirudinaria (Leech), it looses its connection. Ciliated organs are non-functional in adult. It becomes a part of haemocoelomic system and forms coelomic corpuscles.

The different lobes of Nephridium consists of gland cells. It bears intracellular canals or ducts inside. The ducts of different lobes opens into wide central canal. Central canal opens into vesicle after 1 and 1/4 turn.

Process of excretion 0r Physiology of excretion - 

• The ciliated organ is completely separated from the nephridium in adult stage. Ciliated organ has no excretory function in adult but it manufacture coelomic corpuscles of haemocoelomic system.
• The nephridium proper is excretory in function. It serves to eliminate water and nitrogenous wastes from the body. Nitrogenous consists of mainly ammonia. Quantity of urea hence leech is a Ammonotelic.
• Nephridia acts as excretory as well as osmoregulatory organ. Each nephridium is richly supplied with branches of haemocoelomic channels. The gland cells absorb excretory products from the haemocoelomic fluids. Excretory fluid is finally collected in the vesicle of nephridium and lastly expelled out through nephridiopore.
• Nephridia are osmoregulatory in function because maintained water balance in the body. The osmotic pressure of body fluid is always higher than the surrounding water. Hence water enters into the body continuously.
• The Nephridium removes water from the body. Leech has special mechanism in the epidermis, to absorb Na + Cl ions to opens at the loss in metabolism.                                                                      

COELENTERATA- LIFE CYCLE OF OBELIA

 

• In obelia colony, reproduction takes place by asexual methods and produces polyp or hydranth and blastostyle.

1. Polyp or hydranth
2. Blastostyle

• Both are asexual zooids. These two zooids represent asexually generation. Blastostyle, produces medusa. Medusa is reproductive zooids. In medusa four gonads are present.
• In medusa, gonads are either male or female. Therefore, medusa is unisexual.

Gonads

In medusa, gonads are found in sub-umbrellar surface. Gonads are per radial in position. Each gonad is round and formed of interstitial cells. Interstitial cells are present between ectoderm and endoderm.

In male medusa, interstitial cells forming, spermatozoa but in female medusa interstitial cells produces ova.

After the maturity of female or male gonad, ectoderm raptures, and spermatozoa or ova releases in water and swims freely in sea water.

Fertilization

The sperm of one medusa swims in water and reaches to the ova of other medusa. Sperms and ova together fuses. In this way cross fertilization takes place.

Generally, sperms reach to ovum by water current. Sperm is male gamete and ovum is female gamete. Male gamete and female gamete unite to form single zygote.

Development

Zygote divides holoblastic manner. Division of zygote is called cleavage.

Cleavage -  

Zygote first divide to form four celled stage.

First and second cleavage is vertical.

Third cleavage is horizontal, forming eight celled stage.

Then, divides and redivides to form hollow structure called Blastula stage.

 The cavity of Blastula is called Blastocoel.

 The wall of Blastula is one cell thick.

Stereo gastrula 

The cells of Blastula divide and redivide to fill up the Blastocoel cavity. It is called solid gastrula. It is also called stereo gastrula. The outer wall of gastrula is called ectoderm and the inner wall of gastrula is called endoderm. After sometime it elongates and ectodermal cells develops cilia. Gradually in the center a cavity is formed. It is called coelenteron. Now, gastrula changes into planula larva. Planula larva swims in water freely.

Hydrula 

After some times the free swimming planula larva fixes with the free swimming planula larva fixes with any substratum (stone or wooden logs). Now changes took place in planula. The anterior part of planula forms basal disc, but the posterior part of planula forms manubrium. The terminal part of manubrium breaks to form mouth. Many tentacles develop around mouth. This stage is called hydrula. The basal part of hydrula, is called Hydrorhiza. Hydrorhiza grows on substratum and gives vertical branches.  vertical branches grow upward. From the vertical branches buds arises. Due to budding polyp and blastostyle are formed. Gradually, a complex obelia colony is formed. Blastostyle, slowly and slowly form medusa buds and starts sexual generation. Medusa is swimming stage in obelia. It works for dispersal. It is essential for survival.

Alternation of generation or metagenesis

Generally, in the life cycle of particular organism, after sexual generation, asexual generation is found. The beginning of sexual generation starts from sex cells. Sex cells are formed in parent body but asexual generation are formed after division of sexual generation.

The individual of asexual generation don’t bear gonads.

Sexual generation are formed by division of asexual generation. In sexual generation, gametes (female & male) are formed.

 This process in which sexual generation and asexual generation is found alternately is called Alternation of Generation. Today, it is called metagenesis.

In the life cycle of obelia, it is a good example of alternation of generation. This process is going on continuously.

The hydra like colony of obelia is showing asexual generation. But medusa forms sexual generation. The hydroid colony of obelia bears no gametes or sex cells. The colony reproduces, asexually by budding, forming polyp and blastostyle. 

Blastostyle produces medusa. Medusa by sexual reproduction produces gametes. Formation of gametes takes place by gametogenesis.

After the fusion of male and female gametes, zygotes are formed. In this way regularly metagenesis occurs. Although, in obelia true alternation of generation is not found.

Because, hereafter diploid generation, haploid generation is not found. In obelia only gametes are haploid and sexual medusa bears gonads. Gonads are diploid like hydroid form.

Conclusion

In this way medusa is sexual form. It bears sex organs and swims freely. It produces male or female gametes. Sexual and asexual generation is clearly seen in obelia.