Size and fecundity observations of pea crab (Juxtafabia muliniarum) from the paleal cavity of!he oyster Saccostrea palmula were made from May 1998 to May 1999. Infestation frequency was 18.52 % in a sample of 540 oysters. Of 136 pea crabs, 36 % were couples, 60 % were single females and 4 % were single males. The mean caparace length of J. muliniarum was 5.6 + 0.74 mm (range 4.0 to 7.6 mm) for females and 2.7 + 0.60 mm (range 1.6 to 4.0 mm) for males. The mean weight was 0.180 + 0.084 g (range 0.06 to 0.4g) for females and 0.011 + 0.003 g (range 0.01 to 0.02 g) for males. Ovigerous females (43.75 % of all females) were found in all months. The caparace length - fecundity relationship was F = 3904.6 Ln (Lc) -4651.1. The caparace length-weight relationship was P = 6 X 10^-4 Lc^3.2122. The mean sex-ratio was 1.0 male: 2.4 females. Saccostrea palmula infected only by females was the dominant group (60.78 %). This mollusk is a new host record for the crab