|Open polyps on a Nephtheid soft coral|
by B. N. Sullivan
Octocorals (Octocarallia) are a subclass of corals whose polyps have eight tentacles. The name Octocoral derives from this morphological feature [in Greek, "okto" means "eight"].
When the polyps are feeding, the feathery tentacles are spread wide to capture passing bits of nutrients. In macro photos of Octocorals, like the one above, the open polyps look like a dense garden of little flowers.
When the coral polyps are not feeding, the tentacles retract into little balls, like an open hand closing into a fist. To see what I mean, look at these recently posted macro photos of another soft coral with closed polyps.
The Octocoral species pictured above is a a Nephtheid soft coral. I took the photo at Indonesia's Bunaken National Park, a lush marine preserve near the northern tip of Sulawesi Island.