Flame cell in Platyhelminthes

• Excretion in Platyhelminthes through protonephridia/ flame cell:-
Metabolic waste products of flat worms are excreted generally in the form of NH3 by diffusion across the general body surface. Flatness is helpful in diffusion.
However flat worms release excess water as well as some excretory products through flame cells.
• Structure:-
A typical flame cell is an uninucleated large cell.
The flame cell may give out numerous branched protoplasmic processes in the surrounding mesenchyme.
In the center of the cell is a conspicuous (easily visible/ attracting attention) bulbous cavity or cell lumen. The cavity narrows down forming a fine capillary duct.
The cytoplasm occurs in the periphery of the cell containing a round or oval nucleus.
The broad end of lumen encloses a tuft of long cilia or flagella. The tuft of cilia/flagella when undulates, resembles the flickering flame of a candle. Hence the common name is flame cell.
 These cells are usually connected to the lateral longitudinal collecting/excretory ducts.
•  Mechanism of function:-
Flame cells function on the basis of filtration & resorption.
                      [ The water from the intercellular spaces are collected by the extension of the plasmalemma. The collected water is ultrafiltered through the thin wall of pillar like rods. The ultrafiltered fluid (excluding the protein molecules) then moves through the neck of the cavity by the flickering movement of the cilia/flagella.]
                        The continuous beating of the cilia/flagella within the cavity of the flame cell produce sufficient negative pressure which causes ultrafiltration. 
                      The filtered fluid is passed into the longitudinal duct through the capillary duct & discharged through the nephridiopore.
 During passing through the tubes ions are selectively reabsorbed or secreted.                                                                                                                                             The protonephridia thus plays an important role in regulating ionic & water balance in addition to the elimination of metabolic wastes.

Nephridia in Annelida

• Describe the structure of septal nephridia in Pheretima.

The septal nephridia may be considered typical of all the nephridia of Pheretima.

• Structure:-

Each septal nephridium consists of nephrostome , neck, body of nephridium & terminal duct.

1. Nephrostome :-

 Nephrostome is the ciliated funnel communicating with the coelom.

It consists of an elliptical pore bounded by so called upper & lower lips. Upper lip is formed of a large central cell & 8 or 9 marginal cells.

The lower lip consists of 4 to 5 compact cells. All the cells are ciliated.

2. Neck:-

Nephrostome leads into the main body of nephridium through a short, narrow & ciliated, tube like neck.

3. Body of nephridium:-

Body consists of 2 parts - a short straight lobe & a long twisted loop with a narrow apical part.

Twisted loop consists of a proximal limb & a distal limb which are spirally twisted upon each other. Proximal limb is jointed to the neck.

4. Terminal duct:-

Distal limb of the body of nephridium ends in a short & narrow duct called terminal duct.

• Nephridial tubule:-

Nephridium consists of a connective tissue matrix traversed by a coiled tubule. It has 4 ciliated tracts in its course 1 in neck, 2 in body & 1 in terminal duct.

There are 4 parallel tubules in the straight lobe.

Each limb of twisted loop contains 3 parallel tubule in basal part & 2 in the apical part.

A single tubule is present in each of the neck & terminal duct.

• Nephridia in Annelida:-

Nephridia are segmentally arranged coiled tubules formed by the invagination of ectoderm into coelom.

Internally they may end blindly into the coelom (protonephridia) or may open into the coelom by a ciliated funnels or nephrostomes (metanephridia).

Externally they opens through small apertures called nephridiopores.

Nephrostome may open into coelom either in the same segment in which it lies or in the segment just in front.

Nephridia are primarily excretory in function but may secondarily serve to carry genital products to the exterior.

• Protonephridia:-

The 'closed' or protonephridium is the primitive type. It terminates in the coelom as a blind tube.

Their blind ends are fringed with solenocytes. The solenocytes are round ciliated cells connected to the nephridium by a narrow tube. The lumen of the tube encloses a long vibrating flagellum.

Excretory fluid enters through the walls of solenocytes. The fluid is then driven into the lumen of the nephridium by the flagellum & forced to the exterior through nephridiopore.

Protonephridia always develop in the larval polychaetes. They are also found in some adult polychaetes like Vanadis, Phyllodoce, Glycera etc.

• Metanephridia :-

The 'opened' or metanephridia are more advanced. They are found in the majority of polychaetes (Neanthes), all the oligochaetes (Lumbricus) & leeches.

A metanephridium is opened at both ends. It opens into the coelom by a ciliated funnel or nephrostome. The other end of it opens to the exterior through the nephridiopore.

Principal nitrogenous product in annelids is NH3. The excretory products diffuse from coelomic fluid or blood into the lumen of nephridial tubule. It is discharged to the outside through nephridiopore.

1. Micro & Meganephridia:-

On the basis of their size & no. nephridia are divided into 2 groups-

Micronephridia:-

These are smaller in size, sometimes microscopic, & are numerous in each segment. They are networks of fine tubes lying on the body wall & septa in each segment.

All the nephridia of Pheretima are micronephridia.

Meganephridia/ Holonephridia :-

 These are larger in size & generally one pair per segment. They usually extend over 2 segments & their nephrostomes open into the segments next in front.

They are found in Polychaeta & Hirudinea.

2. Exo & enteronephridia:-

Nephridia are termed as exonephric or ectonephric when they directly open to the exterior through nephridiopores.

Such as the meganephridia of Nereis, Hirudinaria, Lumbricus & integumentary micronephridia of  Pheretima.

Nephridia are termed as enteronephric when they lack nephridiopores & open into the excretory or alimentary canal, as septal & pharyngeal nephridia of Pheretima.

Green gland in Crustaceans

• Green gland:-
In decapod crustaceans excretory organs are known as antennary gland or green gland. These glands are opaque-white, pea seed sized structures, enclosed in the coxa of each 2nd antenna.
Each organ consists of 3 parts: 1. End sac 2. Labyrinth or glandular plexus 3. Bladder.
1. End sac:-
 This is a small, bean-shaped structure containing a large blood lacuna.
The wall of the end sac consists of 2 layers-
The outer thick layer consists of connective tissue containing numerous, minute blood lacunae.
The inner thin layer consists of excretory cells having excretory function.
 The wall of the end sac is produced into a number of radial septa, projecting into the central cavity.
2. Labyrinth or glandular plexus:-
 It lies on the outer side of the end sac.
It consists of numerous, narrow, branched & coiled excretory tubules, embedded in a mass of connective tissue with blood lacuna.
The wall of each tubule consists of a single layer of excretory epithelial cells.
The tubules open by a single aperture into end sac & by many apertures into the bladder.
3. Bladder:-
The bladder is the largest part of green gland.
It is a thin walled sac with an epithelial lining.
It communicates with the exterior through a small ureter which opens to the outside by a small rounded renal aperture, present on the base of each 2nd antenna.


• Functional aspect:-
The end sacs excrete mainly compounds of NH3 but uric acid & other nitrogenous compounds are excreted by other parts.
The excretory fluid from end sacs pass into labyrinths.
The greatly folded, glandular labyrinth is the site for selective resorption.
The remaining fluid (urine) passes into the bladders & finally expelled out through renal apertures.
         Therefore the green gland extract nitrogenous wastes as well as maintains ionic & water balance.

Malpighian tubules in Insects

• Malpighian tubules:-
Malpighian tubules are numerous slender, thread like, yellow coloured structures. These are the principal excretory & osmoregulatory organs in insects.
• Position:-
 They are attached to the alimentary canal at the junction of midgut & hindgut.
• Origin:-
Malpighian tubules are ectodermal in origin.
•  Structure:-
The outer layer of the malpighian tubule which is in contact with the haemolymph is composed of thin, elastic, connective tissue & muscle fibres.
The malpighian tubule lumen is lined by cuboidal epithelial cells.
There are 2 distinct regions in each tubule –
A) Distal blind secretory region: - It hangs freely in the haemocoel. The inner cells lining the distal region have well developed brush border.
B) Proximal absorptive region:- It opens into the gut. The inner cells lining this region are less differentiated & have honey comb border.


•  Physiology of excretion:-
       Insects produce nitrogenous waste in the form of potassium urate which is liberated into the haemolymph.
 This along with water is taken up by the distal region of the malpighian tubule.
In the cells of the tubule potassium urate reacts with H2O & CO2 to form potassium bicarbonate & uric acid.
 Potassium bicarbonate is absorbed back into the haemolymph but uric acid is left out in the lumen.                              
 As the uric acid in dissolved condition moves into the proximal region of the malpighian tubule, the H2O is reabsorbed. [ Reabsorption of H2O occurs to such an extent that the basal part of the proximal region becomes filled with solid crystals of uric acid.] Resorption of water further takes place in the rectum.


• Importance:-
Thus the malpighian tubules function excretory as well as osmoregulatory as they not only helps by excreting nitrogenous wastes but also in conserving water in proper amount. This has helped insects in leading effective life activities in terrestrial environment.

Excretion in Mollusca

• Excretion in Mollusca:-
Molluscan excretion takes place by the kidney (organ of Bojanus) & Keber’s organ. The kidney in bivalvian molluscs is known as organ of Bojanus.
Excretion in Unio sp. or Lamellidens sp. takes place by – 1. A pair of organ of Bojanus & 2. Keber’s organ or pericardial gland.
1. Organ of Bojanus:-
Kidneys of bivalves are called organ of Bojanus after the name of the discoverer.
Location:-
These are situated one on each side of the body below the pericardium.
Structure:-
Each kidney or organ of Bojanus is a long, dark tube, open at both ends. It consists of 2 parts -
1.  Brown, spongy, thick-walled, glandular part or kidney proper &
2.  Small, thin-walled, non-glandular, ciliated urinary bladder.
The glandular part of the kidney opens into the pericardium by renopericardial aperture.
The urinary bladder opens to the suprabranchial chamber of the mantle cavity,  by a minute opening, called renal aperture/ nephridiopore.
Physiology of excretion:-
Urine originates as an ultrafiltrate from the heart into the pericardium. 
The glandular part of the kidney extracts guanin & other nitrogenous waste products of metabolism from the coelomic pericardial fluid. Here resorption of the minerals & water takes place.
 The ciliated epithelial lining of the urinary bladder produces an outgoing current which takes away excretory product like NH3 & urea etc. to the outside through renal aperture, suprabranchial chamber & exhalant siphon respectively .
1. Keber’s organ:-
It is also known as pericardial gland. It is a large, reddish brown, glandular mass situated in front of the pericardium, & responsible for the excretion of nitrogenous waste products. The excretory products are discharged into the pericardium from where these are collected by the organ of Bojanus to be discharged to the outside.

Piercing & sucking mouth parts in mosquitoes

Piercing & sucking mouth parts in mosquitoes:-
In mosquito, mouth parts are piercing & sucking type i.e. they are adapted for piercing the tissues of animal or plants to suck blood or plant juice.
The mouth parts consist of labium, labrum-epipharynx, hypopharynx, mandibles & maxillae.


Mouth parts:-
1. Labium:-
 The labium is modified to form a long, straight, fleshy tube called proboscis. It has a deep labial groove on its upper side. At the distal end of labium is a pair of small tactile labella which are reduced labial palps.
Function:-
The labial groove lodges all other mouthparts. During piercing, labella guides the mandibles & maxillae. The whole labium bends back to allow needle like mouthparts to go in the flesh.


2. Labrum-epipharynx:-
The labrum is long & needle like with ventral groove. The epipharynx is fused with the labrum forming labrum- epipharynx.
Function:-
It covers the labial groove dorsally from inside. This structure appears C – shaped in transverse section having a groove called food channel.


3. Hypopharynx:-
Food channel is closed below by a long, pointed & flattened plate, like a double edged sword, called hypopharynx. It possesses a salivary duct, opening at its tip.
Function:-
 Through this duct saliva is poured to prevent coagulation of  blood during sucking.


4. Mandibles & maxillae:-
Within the labial groove lies paired, long, needle shaped mandibles & maxillae. Mandibles end in sharp tiny blades, while maxillae into saw like blades bearing teeth.
Function:-
Mandibles & maxillae act as piercing organs.


In male the labrum-epipharynx & the labium are the same as in the female, but the mandibles & maxillae are very short & functionless & the hypopharynx is fused with the labium.


Mechanism of feeding:-
The normal food of both sexes are nectar of flower & juices of plants, but the female possesses modified mouth parts for obtaining additional meals of blood of vertebrates.
A female mosquito sits on a vertebrate & presses its labellae of proboscis against the skin. Labellae act as a guide for the piercing mandibles & maxillae.
The labium bends back and mandibles & maxillae pierce deep into the skin in order to puncture the blood capillaries.
 Saliva, acting as an anticoagulant, is injected down the hypopharynx into the wound.
The labrum-epipharynx & hypopharynx together form a feeding tube to suck up blood.
The suction is caused by the pharynx by which blood comes into the mouth.

Respiratory structures and function in Arthropoda

• Write a note on book lung of Buthus.

Book lungs are the aerial gas exchange structures of Buthus.

No. & location:-

Buthus  possesses 4 pairs of book lungs situated on the ventro lateral sides in the 3rd, 4th, 5th & 6th mesosomal segments.

Structure:-

Each book lungs consists of 2 parts

1. Atrial chamber:-

The proximal or ventral part is called the atrial chamber. It is a small compressed air cavity.

 The roof of the atrial chamber bears many slit like openings, set parallel with each other. The chamber communicates with the interlamellar spaces of pulmonary chamber through these openings.

The atrial chamber communicates with the exterior through a slit, called stigma.

2. Pulmonary chamber:-

The larger, distal or dorsal part is called the pulmonary chamber.

It contains  about 150 vertical folds or lamellae. The lamellae are lying parallel & are arranged like the pages of a book.

Each  lamella is a hollow structure made of 2 thin layers of membrane united at their end.

The outer sides of the lamellae bear ridges & bristles which keeps the adjacent lamellae apart & an inter-lamellar space is left between them for the for the flow of air.

Blood supply:-

The deoxygenated blood from the ventral sinus is sent to each book lung by a diverticulum.

        Then it enters the lamellae at their bases & is oxygenated.

The oxygenated blood from the lamellae is collected into a pulmonary vein which opens into the pericardium.

Mechanism of respiration:-

Dorso-ventral & atrial muscles control the inflow & outflow of air into the atrial chamber.

On contraction of these muscles air flows out through stigmata.

On relaxation of these muscles fresh air enters into the atrial chamber as well as interlamellar spaces.

Exchange of gases takes place through the highly vascularised walls of the lamellae.

• Write a note on book gills of Limulus.

In xiphosuran, Limulus, the respiratory organs are book-gills.

Location:-

They occur on the posterior wall of the plate like appendages of 5 posterior segments of mesosoma.

Structure:-

They become modified as gills. On each appendage are found some 1500 thin walled lamellae formed by folding of posterior integument.

The lamellae project from the surface & since they lie parallel to each other resembling the pages of a book, they are characteristically known as book gills.

Mechanism of functioning:-

The beating of the appendages causes  a current of water to pass over the book gills.

The blood within the lamellae is separated from the surrounding sea water by only a thin wall. Blood contain respiratory pigment haemocyanin.

 A major ventral blood vessel gives rise to a series of afferent branchial vessels to supply blood to the book gills. After the gas exchange between the water & blood efferent vessels carry oxygenated blood to a large branchio-pericardial vessels leading back towards the heart.

Ommatidium & Statocyst in Arthropods (Prawn)

• Compound eye :-
Each compound eye in arthropods is a composite structure, made up of a large no. of structural & functional units called ommatidia lying radially. A single visual unit is called ommatidium.


• Structure of an ommatidium:- (Prawn)
Each ommatidium is composed of a no. of cells arranged end to end along a central axis as follows-
1. Cornea:-  Cornea is the outermost, transparent, cuticular layer of the compound eye. It is divided into a large no. of facets.  One ommatidium lies below one facet. Each corneal facet thickens in the center to form a biconvex lens.


2. Corneagen cells:- Immediately beneath the corneal facet, a pair of corneagen cells is present.
 They are responsible for the replacement of the facet.


3. Crystalline cone:-  It is a well developed, triangular, transparent body, surrounded by the cone cells.
It works like a second lens.


4. Cone cells:- Beneath the corneagen cells lie 4 elongated cone cells or vitrellae.
It constitute or nourish the crystalline cone.


5. Rhabdome:- It is an elongated, spindle shaped, transversely striated body.


6. Retinal cells:- These are a group of 7 elongated cells. The distal part of these cells are dilated containing nuclei.
Retinal cells surround, secrete & nourish the rhabdome.


7. Basement membrane:- Inner ends of retinal cells rest upon a basement membrane beyond which they are connected with sensory nerve fibres.


8. Pigment sheath:- Each ommatidium is separated from the neighboring ommatidia by a sheath of dark pigment. It is formed by surrounding amoeboid chromatophores which are arranged in 2 groups.
               The proximal group surrounding the rhabdome forms retinal pigment & the distal group surrounding the crystal cone forms the iris pigment.


• Statocysts:- (Prawn)
The statocysts are a pair of small, white, bead like, cuticular, hollow, spherical sacs.


• Position:-
A statocyst lies inside the basal segment or precoxa of each antennule, attached to its dorsal wall. It opens dorsally on the concave surface of the precoxa through a minute statocystic aperture.
A small statocystic branch of antennular nerve supplies the statocyst.


•  Structure of a statocyst:-
On cutting a section of the statocyst, its cavity is found full of minute sand particles.
 On removing them, it is found that there is an oval ring of elongated, delicate, receptor setae attached to the inner wall.
Each receptor setae consists of a swollen base & a filamentous shaft which is sharply bent about the middle of its length. The shaft bears fine bristles beyond the bend.
Each receptor seta is innervated at its base by a fine branch of statocystic nerve.


• Function:-
Statocyst perceives the direction of force of gravity & functions as the organ of  orientation & equilibrium.
The sand particles  serve as statoliths. Any change in the position of the swimming prawn causes a corresponding displacement of sand particles. This displacement press against some of the sensory setae & stimulate them.
Stimulated setae convey the information to brain through nerves, so that the animal corrects its position.

Tube feet of Echinoderms

1. Tube foot:- A podium or tube foot is a short, hollow, elastic, thin walled, closed tube present in the ambulacral groove of arms in echinoderms.
Each tube foot extends through a gap, called ambulacral pore, which lies between 2 ambulacral ossicles. 
Structure:-
Each tube foot can be distinguished into 3 regions:-
1. Ampulla:- A rounded sac like structure.
Position:- Situated above the ambulacral ossicles & projects into the coelom.
Wall:- The walls of ampulla possess circular muscles which are provided vertically.
2. Podium:- It is the middle tubular portion.
Position:- It is extending through the ambulacral groove.
Wall:- The wall of each podium is covered on the outside by an ciliated epithelium & internally with peritoneum. Between these 2 layer lie connective tissue & longitudinal muscle fibres.
3. Sucker:- The lower end of the podium is flattened forming a cup like structure called sucker.
Function:-
1. Tube feet help in locomotion by anchoring the substratum tightly.
2. These also helps in capturing  & handling the food.
3. Thin walls of tube feet may serve for respiratory exchange of gases.





Mechanism of locomotion in echinoderms:-
            The entire w.v.s. acts as a hydraulic system during locomotion.
1. Water enters through the madreporite to different canals such as, stone canal → ring canal → radial canals → lateral canals.
2. From lateral canals water enters into the ampulla of the tube feet.
3. Body is moved by the stepping action of tube feet which are alternately adhered & raised from the substratum.
4. One or 2 arms, in the desired direction of movement, are raised from the substratum. 
5. Simultaneously the vertical circular muscles of the ampullae of the tube feet of these arms contract & the valves of the lateral canals close.
6. This increases hydrostatic pressure within the tube feet.
7. The tube feet consequently elongate, extend forward.
8.  Podial suckers adhere to the substratum by suction force as well as the adhesive secretory products of the tips of tube feet.
9. Then by muscular activity, tube feet assume a vertical posture, dragging the body forward.
10. Tube feet then shorten by contracting their longitudinal muscles, forcing the water back in to the ampulla.
11. Consequently the suckers release their hold on the substratum.
 During movement 1 or 2 arms act as leading arms& all the tube feet extend in the same direction in a coordinated manner.

Flagella & Cilia

Ultrastructure of Flagellum:-

Electron microscopy has shown that the flagellum has 3 parts:

1. Outer coat:- A contractile membranous sheath that is physically continuous with the cell membrane but it contains far less amount of protein than the latter.

2. Matrix:- The bounded space of flagellum contains a watery substance known as matrix. The axoneme is embedded into it.

3. Axoneme:- It is the inner core, composed of microtubules & other proteins.

Here microtubules are modified & arranged in a ring of 9 doublets surrounding a pair of central singlet. This arrangement is known as ‘9+2’ array.

Each of the central microtubule is complete & composed of 13 protofilaments. Both central microtubules are connected by a bridge & are enclosed in a common central sheath.

Each of 9 peripheral doublet consists of 2 microtubules, one is smaller (A) & complete, having 13 protofilaments & lying closer to axis ; the other microtubule (B) is larger & incomplete, having only 11 protofilaments.

• Major protein structures of axoneme:-

Axoneme component	Function
Tubulin	Principal component of microtubules.
Dynein	Project from microtubule doublets & interact with adjacent doublets to produce bending.
Nexin link	Hold adjacent microtubule doublets together.
Radial spokes	Extends from each of the 9 outer doublets inward to the central pair.
Sheath projections	Project as a series of side arms from the central pair of microtubules; together with the radial spokes these regulate the form of ciliary beats.

Flagellum arises from a basal body. The ultrastructure of basal body is like those of an axoneme except that the central singlets are absent & 9 fibrils in the outer circle are triplets. 2 of these microtubules are continuous with the doublet of the flagellum. Dynein arms are absent in triplets.

 Q. Mention the differences observed in cilium & flagellum.


Ans. :-
Morphologically & physiologically the cilia & flagella are identical structures but both can be distinguished from each other  by their no. , size & functions    
1. The flagella are less in no. (1-2) in no. than the cilia which may be numerous (3000-14000) in no.
2. Flagella occur at one end of the cell, while the cilia may occur throughout the surface of the cell.
3. The flagella are longer processes while the cilia are short appendages of the cytoplasm.
4. The flagella usually beat independently, while the cilia tend to beat in a co ordinated rhythm.
5. The flagella exhibit undulatory motion while the cilia move in a sweeping or pendular stroke.


17. Write a note on the basal body of cilium.
The basal body is a centriole like cellular organelle from which the cilium arises. It remains separated from cilium by a basal plate. The ultrastructure of basal body is like those of an axoneme except that the central singlets are absent & 9 fibrils in the outer circle are triplets. Each triplet contains one complete 13-protofilament microtubule, the A tubule, fused to the incomplete B tubule, which in turn is fused to the incomplete C tubule. 2 (A,B) of these microtubules are continuous with the doublet of the flagellum. Dynein arms are absent in triplets.


17. What is axoneme?
Axoneme is the inner core of cilia or flagella, composed of microtubules & other proteins. Here microtubules are modified & arranged in a ring of 9 doublets surrounding a pair of central singlets.


17. Mention different flagellar movements in mastigophorans.


Flagellar movement is characteristic of Mastigophorans which bear one or more flagellum. The flagellum requires liquid medium for movement.
3 types of flagellar movements have been recognized.


1. Paddle stroke:-
According to Ulhela & Krijsman (1925) the common movement of flagellum is sideways lash. It consists of an effective downstroke/ power stroke with flagellum held out rigidly & a relaxed recovery stroke with flagellum strongly curved. The power stroke produces more thrust in the backward direction & as a result the animal moves forward.


2. Undulating motion:-
Wave like undulations of the flagellum, when proceeds from tip to base, pull the animal forward. Backward movement is caused when undulations pass from base to tip.


3. Simple conical gyration;-
According to Butschli's screw theory the flagellum performs spiral turning like a screw. This exerts propelling action which pulls the animal forward through water with a spiral rotation as well as gyration around the axis of movement.


Q.   Describe the different types of flagella in protozoans.


 Flagella are the locomotor organelles of the mastigophoran protozoans. A typical flagella consists of central axoneme made up of 2 longitudinal microtubules enveloped by a central sheath & 9 pairs of peripheral longitudinal microtubules. All 20 fibres lie in a matrix of dense cytoplasm & covered by extension of cell membrane. They fuse at the base to join a basal granule or kinetosome.
              Flagella may be surrounded by very minute, fine, flexible lateral processes called mastigonemes.
   Flagella are classified based on the arrangement of mastigonemes and the nature of the axial  filament.
  There are five types of flagella. They are-
1.  Stichonematic:  When the  mastigonemes are present on one side of the flagellum, it is called stichonematic flagellum.  .
       e.g.  Euglena, Astasia
                                                     
2.  Pantonematic: When two or more rows of mastigonemes are  present on both sides of flagellum, it is called Pantonematic flagellum.
       e.g. Paranema ,Monas
                         
3.  Acronematic: When the mastigonemes are absent and the distal ends of the flagellum ends as a terminal, 'naked', axial  filament it is called acronematic flagellum.
        e.g.  Chlamydomonas, Volvox
                                           
4.  Pentachronematic: When the mastigonemes are present on 2 rows on the lateral sides of the flagellum but the flagellum ends in a terminal, naked, axial filament, it is called pentachronematic flagellum.
        e.g.  Urceolus
                                                
5. Anematic: When the flagellum is simple without mastigonemes and/or terminal naked filament are absent, it is called anematic flagellum.
        E.g.. Chilomonas, Chryptomonas.
Infraciliary system of ciliates:-


Modification of cilia:-


The cilia may form the following composite motile organelles.
1. Membranelles:- These are membranes formed by fusion of 2 or more adjacent transverse rows of short cilia. They are found in the peristome making powerful sweeps.
2. Undulating membranes:- These are made up of one or more longitudinal rows of cilia fusing together. They are found in the peristome or cytopharynx & are used for food collection eg. Vorticella.
                     the undulating membrane of Trypanosoma is only a web of ectoplasm, it is not made up of cilia & it is locomotory.
3. Cirri:- Cirri are formed by 2 or 3 rows of cilia on the ventral side of some ciliates. They are locomotory & they may also be tactile.


Mechanism of ciliary locomotion:-


       During swimming each cilium moves in a whip like motion.
               It first gives a forward active/effective stroke in which the cilium is fully extended beating against the surrounding liquid.
               It is followed by a recovery stroke in which the cilium returns to its original position with an unrolling movement that minimizes the viscous drag (drag:-resistance to motion: the resistance experienced by a body moving through a fluid medium).
              Cilia of the same transverse row beat together & those of the same longitudinal row beat one after the other. This coordinated movement pattern of the cilia is called metachronal rhythm. It can be compared to the passage of wind over a field of paddy.
              Such type of movement is regulated by a highly complicated neuro-motor system.