Skeletal eroding band (SEB) is a disease of corals that appears as a black or dark gray band that slowly advances over corals, leaving a spotted region of dead coral in its wake. It is the most common disease of corals in the Indian and Pacific Oceans, and is also found in the Red Sea.
So far one agent has been clearly identified, the ciliate Halofolliculina corallasia. This makes SEB the first coral disease known to be caused by a protozoan. [citation needed] When H. corallasia divides, the daughter cells move to the leading edge of the dark band and produce a protective shell called a lorica. To do this, they drill into the coral's limestone skeleton, killing coral polyps in the process.
A disease with very similar symptoms has been found in the Caribbean Sea, but has been given a different name as it is caused by a different species in the genus Halofolliculina and occurs in a different type of environment.