The pea-crab Pinnotheres latissimus B?URGER occurs frequently in Hakata Bay living commensalistic with a pullet, PaNhia (Tapes) philippinarum. Berried crabs are to be found in summer, the zenith of the season falling in July. The eggs are of apricot orange colour, changing to cream yellow when ready to hatch out. Early eggs measure 0.33 mm in diameter, late eggs 0.42 mm. Berried crabs taken out from bivalves were reared in fingerbowis containing some seawater and sand. Pre-zoea hatched out from the eggs would still remain on the abdomen of the mother crab. Pre-zoea : 1.15 mm long; antennules and antennae rudimentary, abdomen with 5 segments plus telson ; telson with 3 lobes of the F1-type. Pre-zoea cast the embryonic cuticle and become first zoea. First zoea : 1.2 mm long. At first it comes up to the surface of water, then in one day or two it descends to the bottom curling up its body in the shape of a ball. Carapace rounded, without spines, antenna rudimentary stumps of the D-type; first and second maxillipeds with 4 swimming hairs on the exopodites, endopodites with 5 and 2 joints respectively; abdomen with 5 segments plus telson, second and third segments with lateral knobs. Second zoea have all the features similar to those of t h e first zoea, except the differentiated mouth parts. Hair formula : 3-4?n, 4, 3-0. The following 4 characters are observed as stable: I. Spines totally absent. 2. Antenna of the D-type. 3. Telson of the F,-type. 4. Hair formula: 3-4?n, 4, 3-0. Comparing these points in all the species of Pinnotheres hitherto reported one can find that they all have antenna of the D-type and telsons of the F,-type. Thus Pinnotheres is distinguished from the other genera only by two characters of the antenna and telson. The other two stable features of zoea serve to distinguish the species inside the genus Pinnotheres.