Abstract
Sexual dimorphism of Palaemon pacificus and P. serrifer were investigated during 1987 to 1989 in Tateyama Bay, Chiba Prefecture. It was found that both the rostral length and the number of segments of the inner branch of the bifurcated outer flagellum were larger in males than in females. The difference between male and female appeared nearly the size of the minimual ovigerous female. Difference between male and female on both the rostrum and the inner branch of the bifurcated outer flagellum appeared with maturing.
