Which chemical is synthesized by some sponges and acts as an antibiotic

silica
calcium carbonate
cribrostatin
streptomycin
spongin

silica-nope, inorganic, not antibiotic
calcium carbonate-nope, inorganic, not antibiotic
cribrostatin-??? perhaps this one.
streptomycin-produced by molds, not sponges, even though an antibiotic
spongin-made-up word?