The muscular abdomen has six segments and has a thinner shell than the carapace. Each segment has a separate overlapping shell, which can be transparent. The first five segments each have a pair of appendages on the underside, which are shaped like paddles and are used for swimming forward. The appendages are called pleopods or swimmerets, and can be used for purposes other than swimming. Some shrimp species use them for brooding eggs, others have gills on them for breathing, and the males in some species use the first pair or two for insemination. The sixth segment terminates in the telson flanked by two pairs of appendages called the uropods. The uropods allow the shrimp to swim backward, and function like rudders, steering the shrimp when it swims forward. Together, the telson and uropods form a splayed tail fan. If a shrimp is alarmed, it can flex its tail fan in a rapid movement. This results in a backward dart called the caridoid escape reaction (lobstering)
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