Question

3a. What are the parts of the tail of the crayfish? How does the crayfish use its tail? How can this be important in survival?

3b. How many pairs of walking legs (counting the chelipeds) does the crayfish have? The walking legs, like the other appendages, demonstrate the principle of serial homology. Use the study guide to explain this principle.

3c. What are the three pairs of appendages that handle food and bring it to the mouth? What are the hard, jaw like structures? How do they work in the crayfish?

Answer 1

Crayfish or crawfish are crustaceans of order Decapoda,phylum Arthropoda.Crayfish are nocturnal and onmivore.The body of crayfish is divided into two segments.Cephalothorax is the first segment.It is the fusion of head and thorax.It consists of head,maxillae,mandibles and maxillipeds.There are 13 segments in cephalothorax.The next segment is the abdomen.It has 6 segments.

3a.The parts of tail are uropod and telson.There are six segments in abdomen.The sixth segment contains uropods and the middle ofuropod bear a structure called telson.These together make a tail fan.Tail helps crayfish to swim backward by forcing the water forward.The tailfan helps it for survival as a escape mechanism against predators.It is called caridoid escape reaction or tail flipping.It is an innate escape mechanism in most of the crustaceans.In this reaction they produce powerful swimming strokes that pushes its body backward ,away from danger.The response depends upon which part of the body is stimulated.

3b.Counting the cheliped there are five pairs of walking legs.There are four pairs of walking legs in the four segments of thorax and one pair of cheliped in the front of the thorax.Chelipeds are used for capturing prey,gathering food ,defending etc.Walking legs are used for locomotion.Cheliped and walking legs have high structural similarity.Serial homology is a repeating relation between the segments of same organism.The structures arrenged in series in an orgamism will have similarity performing diverse functions.The walking legs like other appendages demonstrate the principle of serial homology.In crayfish ,there are 19 pairs of appendages.All appendagse are built in the similar structural pattern but performs different function.The appendages like uropods,swimmerets,walking legs,chelipeds,mouthpart appendages,antenna and antennule perform diverse functions but hane siilarity in their structural organization.

3c. Three pairs of Maxilliped are the appendages that handle food and bring it to mouth.They are located at the ventral and forward part of the thorax region.Hard jaw lke structures are the Mandibles.They are used to break hard substances like shell of aquatic animals and to crush the food.Two pairs of maxillae hold and tear the food.