Little is known about the biology of Indo-West Pacific ornamental crustaceans, including the peacock-tail shrimp Periclimenes brevicarpalis (Schenkel, 1902) (Palaemonidae Rafinesque, 1815), a species that is highly valued by aquarists and marine photographers. We provide information about gender expression and sexual dimorphism in P. brevicarpalis. We studied a population inhabiting the Haddon's carpet sea anemone Stichodactyla haddoni in the Gulf of Mannar, Tamil Nadu, India. In the studied population, males attain similar maximum and average body sizes (carapace length) than females. This observation and the absence of transitional individuals exhibiting male (appendices masculinae) and female (eggs underneath the abdomen) reproductive traits, ruled out sequential and simultaneous hermaphroditism in P. brevicarpalis and suggest that this species is gonochoric. Minimal differences in claw size (males > females) were observed between the two sexes. The allometric growth of this structure was greater in females than males. The absence of sexual dimorphism in terms of body size concomitantly with the minimal differences in weaponry observed between the two sexes suggest that the species is monogamous, an inference also supported by the common observation of pairs of shrimps inhabiting the same host individual in the field. Additional studies on the behavioral ecology of P. brevicarpalis should reveal its mating system.