Abstract
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 as the two emergence rates during the expected tidal time, the HT & LT (5.6 & 4.6 ind.) were not statistically different from the overall average. When crabs were placed under constant darkness (DD), they showed rhythmic emergence activity during the expected daytime period (3.8 ind.), compared with the activity during the night-time (1.5 ind.), indicating an endogenous agent controlling the circadian rhythmic behavior. Under constant illumination (LL), the crabs showed high emergence activity during both, the expected daytime (6.17 ind.) and expected night-time (6.32 ind.), which shows the control of the exogenous light factor over the locomotion of the crabs. The second aim of this study was to describe the first larval stage of C. boulengeri for the first time through the breeding of egg-carrying females. The distinguishing characteristics of the crab from the other species close to it are described. Keywords: Chiromantes boulengeri; Emergence rhythms; Intertidal zone; Shatt Al-Arab River; Basrah.