The mouthless crab Cardisoma crassum is an important socioeconomic fishery resource; thus, understanding its distribution pattern is key for its fishery management. The present study aimed to determine if mouthless crabs show segregation by size in contrasting habitat types. Three plots were sampled from February to June 2022 to collect data on biometric variables in Ponuga, Veraguas, Panama Pacific. A total of 151 crabs with average cephalothorax width of 56.24 ± 8.56 mm were captured; 97 were male and 54 were female. This proportion difference was significantly skewed towards males at 1.8:1. Subjects from plot 1 were larger and heavier than those from plots 2 and 3. Ovigerous females were found only in plots 1 and 2 during June (rainy season). The minimum cephalothorax width of functionally mature females was 47.11 mm. By this measure, mature females were present in higher proportions in all plots and were significantly more abundant in plot 1. Small crabs were segregated in plot 3; the plot of origin and size were significantly associated. This is the first report of segregation by size in Cardisoma crassum. The findings highlight the importance of habitat features and lead the way for further studies on the factors influencing this distribution pattern.