The Puerto Rican sand crab, Emerita portoricensis, is a species of "sand crab" belonging to the genus Emerita, which is native to the main island of Puerto Rico and its archipelago. The most detailed study conducted on the species was conducted by Sastre between 1988 and 1992. This investigation determined that the species has diotic traits and that there are size and survival differences between sexes. Both sexes reach sexual maturity three months after birth. At this age females are 7 mm (¼ in) in length; their maximum shell size is 19 mm (¾ in). The growing rate is slower in male specimens these being only 5 mm ( in) in length when they reach sexual maturity with a maximum shell size of 11 mm (½ in). In terms of reproductive aspects, females fecundity increases with their size, the males reproductive contribution decreases as they grow older.