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Submitted by Mousumi Sepai, Last Modified on 2021-03-15

Mastax is a peculiar structure characteristic to rotifers. Mastax is actually the muscular pharynx part of the body which is containing the inter-connected movable chitinous pieces which are acting as jaws. It has created lot of interest among different workers, all over the globe. Some researchers suggest it to be a digestive component while others used it for the classification of rotifers.

Inner wall bears masticatory apparatus, the inner epithelium of which bears seven interconnected, projecting hard cuticle made pieces or trophi, composed of an acid mucopolyssacharide materials. On the basic of structure of trophi, mastax may be of different types like- Malleate, Virgate, Caudate, Forcipate, Incaudate, Remate and Unicate.

Structure of a typical mastax:

The mastax or pharynx is a highly muscular chamber with cuticular lining and appendages, complicated structure which varies in shape and size like, rounded, trilobed or elongated. The inner walls bears masticatory apparatus, the inner epithelium of which bears seven interconnected, projecting large, hard, cuticularised interconnected pieces called jaws or trophi or dental mill used to grasp, cut and grind the food is composed of an acid mucopolyssacharide materials.. For some parasitic species this part is modified for help to attach with the host’s body, and for some species trophi is used to suck food in through the mouth.

The seven cuticularised plates in inner epithelium, composed of an unpaired fulcrum and paired rami, unci and manubria. Incus is the composed structure of fulcrum and rami , and malleous is together composition of unci and. Also there is a mid ventral forked fulcrum called anvil or incus.

The fulcrum consist two lateral triangular rami, and on the both side side of incus there is a malleus which is hammer-shaped and bears of an anterior toothed part or uncus and elongated handle-like manubrium embedded with muscles whose posterior end is known as cauda.


Muscular supports to mastax:-

1. Abductor muscles open at the rami.
2. abductor muscles close to the abductor muscles.
3. Fulcro-manubricus between the fulcrum to manubrium.
4. Ramo-manubricus from rami to manubricum.
5. Flex or mol-allows unci to move against rami.
6. Uncus muscles-connect unci to both end of manubrium.
7. Adductor muscles-continous band is pharynx wall between caudae and manubrium. This is the principle muscle producing the chewing movement.
8. Lateralis Manubri-similar to adductor muscle.
9. Abductor and adductors of caudi.

Muscles connecting the trophi to mastax:-

1. Fulcro-oralis from fulcrus to buccal field and adjacent part of the head.
2. Fulcro mucous from fulcrum to pharynx between the ramai and act as piston muscle in virgate mastax.
3. Fulcro-oesophagus-falcrum to oesophagus.
4. Scapules from falcrum to pharynx wall by muscle band.

The lumen of the mastax is lined by cuticle and is ciliated only in case of current feeding forms with remate masax i.e. the forms belonging to the class digonote Rotaria and philodina. The wall has an epithelium. This epithelium secretes the trophi and numerous muscles of the mastax appear to be fibrillar extension of its cytoplasm.

Salivary glands:-

There is About 2-7 salivary glands are attached to the wall and within the ducts, specially the ventral pairs, which are open anterior to trophi or near the mouth or in the buccal tube. The main function of the salivary glands are related with digestion.


1. Mastication- by rubbing and grinding.
2. Grasping prey like the jaws in case of predaceous forms.
3. Attachment to host as in parasitic forms.

Modification of mastax:-
On the basis of structure mastax have several types,

  1. Malleate:- This is most primitive type. All the pieces are relatively stout. Rami are untoothed but Unci are with curved plates(teeth) on their dorso-median side which help grasping, grinding and chewing. This type is the feature of the family branchonidae, trochospeeridae and testudenenidae.
  2. Sub-malleate:- Rami slender,manubri twice as long as unci, other structures similar to that of malleate. This type occurs in some members of Brachionidae.
  3. Virgate:- Fulcrum and manubri are elongated and rod-like. Rami are broad triangular plate and provides mechanical strength to the piston. Unci bear teeth which help grasping the prey. The prey is sucked by the action of piston(hypopharynx). The anterior dorsal wall is stiffened by the cuticular plates i.e. the epipharynx occur in Trichiceridae, Gastropodidae, Synchetidae, Notomatidae.
  4. Caudate:- Epipharynx present manubrium is forked, piston is lacking. Sucking is done by the movement of unci. Occurs in Lindia sp.
  5. Forcipate:- All pieces are slender and elongated. Curved rami with fulcrum form forcep like structure. Sharp teeth are closely approximated to the pointed unci. This occurs in the members of the family microcodonidae.
  6. Incaudate:- It is similar to that of forcipate type and appears to have forcep like shape manubria are rudimentary but stout. These occur in the members of the family Asplancknide.
  7. Remate:- Fulcrum and manubrium are very much reduced. Unci large and plate like. Surface is provided with several parallel ridge forming a masticatory apparatus. It occurs in the members of the order Bdelloida(rotaria).
  8. Malleoramate:- Manubrium looped, incus wide, provided with a number of slender, elongated parallel teeth. It occurs in the members of the family trochosphaeridae.
  9. Uncinate:-Fulcrum and manubrium are reduced. Unci with a few teeth. Rami stout and large subunci present. It occurs in the members belonging to the order collothecaces.
  10. Fulcrate:- A median elongated piece presumably the fulcrum is present. The anterior end of it is attached to a pair of limb like manubria, and several other small pieces. It occurs in the members of order scisonacae.

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