A new sponge species Coelocarteria agglomerans sp. nov. (Isodictyidae: Mycalina: Poecilosclerida) is described from the reef slopes of Bunaken National Marine Park, North Sulawesi, Indonesia. The new species can be separated from the other two congeneric species: C. singaporensis and C. spatulosa by several characters concerning sponge surface, fistule shape, form and size of the spicules and habitat. In detail it differs from C. singaporensis in the presence of strongyles instead of oxeas as main megascleres and of spines in the shaft of palmate isochelae. It differs from C. spatulosa in the absence of characteristic fistules with spatula shaped hoods and in spicule size, because both categories of strongyles and palmate isochelae are remarkably larger in the latter.