PALAEMON (FRESHWATER PRAWN) APPENDAGES

  • Indian River water prawn is called Palaemon'. Marine water prawn is called Penacus'.
  • The body of the prawn is divis­ible into Cephalothorax and abdomen.
  • Cephalothorax is made by 13 segments which includes cephalic and thoracic re­gions.
  • The cephalic region contains 5 segments and thoracic region contains 8 segments.
  • In the abdomen 6 segments are present.
  • The cephalothoracic region is covered by a carapace, k produces anteriorly a rostral spine.
  • In the abdomen the segments are clearly seen.
  • Each seg­ment is covered on dorsal side by a convex tergal plate and a ventral thin sternal plate.
  • Both are connected on the sides by pleuron.
  • In the abdomen the appendages are attached to small plate, called Epimeron on the pleuron.

 

Cephalothoractc appendages :

  • These are 13 pairs.
  • First 5 pairs are called Cephalic appendages.
  • The next 8 pairs are Thoracic appendages.

Cephalic appendages :

  • Antennules: The protopodite is 3 segmented, with basal structure precoxa.coxa and basis.
  • In the precoxa a statocyst is present.
  • It maintains equilibrium of the animal.
  • On the basis 2 long,many segmented whip like feelers are present. They are tactile sense organs.
  • They are not homologous to exopodite and endopodite.
  • The outer feeler is further divided into an inner smaller branch and outer larger branch.

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Antenna: The protopodite shows coxa and basis.

  • Endopodite is long feeler like structure, which is a tactile sense organ.
  • The exopodite is plate like and it is called Squama.
  • It works as a balancer during swimming.
  • At the base of the coxa renal opening is present.
  • Antenna is sensory, excretory and balancing in function.

Mandibles: They are present on either side of the mouth.

  • The basal part of coxa is divided into two parts, it shows a mandibular and incisor process.
  • The mandibular process shows 5 or 6 dental plates.
  • The incisor process shows 3 teeth. On the outer margin of the head a mandibular palp is present, which represents the basis and endopodite.
  • The exopodite is absent. The mandibles are masticatory in function.

I Maxilla or Maxillula : The protopodite is 2 lobed. They are called Gnathobases.

The endopodite is slender. Exopodite is absent.

It helps in the manipulation of the food.

II Maxillae: The protopodite is fait and is divided into 4 lobes.

  • Endopodite is small and unsegmented.
  • The exopodite is broad, and plate like structure.
  • It is called Scaphognathite or baler. It is useful to bring in water into the branchial region.
  • It is helpful for respiration and manipulation of food.

Thoracic appendages :

  • They are 8 pairs.
  • The first 3 pairs are Maxillipedes.
  • The remaining 5 are walking legs.
  • I Maxillipede: They are thin and leaf like.
  • Protopodite is 2 segmented. The endopodite is short.
  • Exopodite is present.
  • It is bilobed. Epipodite is respiratory in function.
  • It is present on the outer side of coxa.

II Maxillipede: It has 2 segmented protopodite.

  • Coxa bears a conical epipodite and a gilk Endopodite is 5 segmented.
  • The five segments are ischium, merus, carpus, propodus and dactylus. Exopodite is long and unsegmented.

III Maxillipede : It looks like a walking leg. It has 3 segmented endopodite.

  • The basal segment corresponds to ischium and merus.
  • The apical segment is fused and corresponds to propodus and dactylus.
  • The middle one is carpus.

4. Walking legs: They are 5 pairs.

  • The first 2 pairs are chelate and the other 3 pairs are nonchelate.
  • They are useful for walking.
  • The typical walking leg has a two jointed protopodite and 5 jointed endopodite.
  • The protopodite has two segments, coxa and basis.
  • The endopodite has ischium, merus, carpus, propodus and dactylus.
  • In the first and second pairs of legs the propodus is prolonged beyond its articulation with dactylus and it looks like a chela or pincer.
  • Such legs are called chelate legs. They catch the food and push it into the mouth.
  • The second chelate, leg in male is larger and powerful than in females.
  • The 3rd. 4th and 5th walking legs are non chelate.
  • In female the 3rd walking leg bears a female reproductive opening on the inner side of coxa.
  • In the male the genital opening is present on the arthrodial membrane between the thorax and 5th walking leg.

Abdominal Appendages:

  • Abdomen bears six pairs of appendages.
  • Each appendage is biramous. These are called pleopods or swimmerts.
  • The protopodite has coxa and basis. The basis bears two flat leaf like exo and endopodite.
  • From the inner margin of the endopodjte a small appendix interna arises.
  • In the females during breeding season the appendix interna of opposite appendages unite and carry eggs.
  • In the first pair of abdominal appendages the appendix interna is absent.
  • The second abdominal appendages of male shows appendix masculine also.
  • The sixth pair of abdominal appendages will be called Uropods or tail feet.
  • They are large and lie one on either side of the telson.
  • The two uropods and telson together form a broad tailfin.
  • It helps the Prawn to take a backward spring in water.
  • In a uropod the coxa and basis fuse together to form a triangular sympod.
  • It helps the Prawn to take a backward spring in water.
  • In a uropod the coxa and basis fuse together to form a triangular sympod. It bears exo and endopodites.

Thus the appendages of Prawn are helpful in food collection, respiration and locomotion.