BARRICADE BUILDING AND NEIGHBOR BURROW-PLUGGING IN ILYOPLAX-NINGPOENSIS (BRACHYURA, OCYPODIDAE)

The small ocypodid crab Ilyoplax ningpoensis exhibits two mud-using te rritorial behaviours against burrow-holding neighbours: building a bar ricade near the neighbour's burrow, acid plugging the neighbour's burr ow while the neighbour is in that burrow. Most barricade-builders and pluggers were large-sized males and, in general, barricade-builders an d pluggers were larger than their opponents. Activity space of a barri caded crab was biased toward the side opposite the barricade. When the barricade was removed, the crab freed from it advanced toward the bar ricade-builder's burrow, suggesting that the barricade functions to de ter the neighbour's approach. In neighbour burrow-plugging, the time t o the pluggee's reemergence was mostly less than 5 min. The pluggee's activity site, immediately after reemergence, was not always shifted f arther from the plugger's burrow. These features of barricade building and neighbour burrow-plugging are compared with those of three congen eric species that have been so far described.