The rhythmic behavior of emergence (locomotion) activity outside the burrows of the crab Chiromantes boulengeri (Calman) collected from the intertidal habitat of Shatt Al-Arab River, Basrah, Iraq, was studied in the laboratory, with three light regimes (using 10 adult crabs, for 5 consecutive days for each light regime). Under natural illumination (daytime: night-time), the study revealed that the crabs exhibited high locomotor activity (M= 7.1 ind.) during the daytime that was significantly higher than the night-time (M= 4.1 ind.). The result showed no relationship between the locomotor activity of the crabs and the two daily tidal cycles. When crabs were placed under constant darkness (DD), they showed rhythmic emergence activity during the expected daytime period, indicating an endogenous agent controlling the circadian rhythmic behavior. Under constant illumination (LL), the crabs showed high emergence activity during both the expected daytime and night-time, which shows the control of the exogenous light factor over their locomotion. Additionally, the study described, for the first time, the first larval stage of this species through laboratory hatching and rearing of egg-carrying females.