Complex sentence: Fire coral, "millepora" spp is a hydrozoan which has stinging nematocysts on its surface., but the chief danger of fire coral is to snorkellers or drivers brushing against it.
Split into simpler sentences: Fire coral, "millepora" spp is a hydrozoan which has stinging nematocysts on its surface. The chief danger of fire coral is to snorkellers or divers brushing against it.