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.

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.