_:b1218287 . _:b1218287 . _:b1218287 "Wikipedia:Sponge_reef"^^ . _:b1218287 . _:b1218287 "A marine sponge reef is marine reefs primarily built by marine sponges. The primary frame-building sponges are all members of the order Hexactinosa. They are found only in glacier-scoured troughs of low-angle continental shelf. The seafloor is stable and consists of rock, coarse gravel, and large boulders."^^ .