 The Caribbean chicken-liver sponge "Chondrilla nucula" secretes toxins that kill coral polyps, allowing the sponges to grow over the coral skeletons.Others, especially in the family Clionaidae, use corrosive substances secreted by their archeocytes to tunnel into rocks, corals and the shells of dead mollusks.Sponges may remove up to per year from reefs, creating visible notches just below low-tide level.