There’s an entire group of hard corals that masquerade as soft corals: large polyp corals of the Indo-Pacific. Their soft, flowing appearance hides a hard calcium-carbonate skeleton, and although divers commonly mistake them for soft corals, there are a few ways to identify them properly.
First, look closely at the coral and search for any places where the polyp may be closed. This area will show the hard skeleton. Second, look for the number of tentacles on the end of each polyp. On species like the Goniopora flowerpot coral, it’s easy to see these long, flowing polyps have far more than eight tentacles, which is a telltale sign that it’s not a soft coral.
If you’re new to coral identification, check out this article on coral biology, where we explain how to identify the difference between hard and soft corals. And if you’re new to Indo-Pacific coral identification, make sure to check out our introduction to these corals as well.
Large polyp corals generally feature a bright color and flowing texture. The general term “large polyp” describes coral species with polyps that are more than few centimeters wide. But it’s important to remember that not all coral will fit into one category and it depends on their different stages of growth. Here are four easily identifiable large polyp corals to look for on your next dive.
Plerogyra is the first large polyp coral divers are surprised to learn is a hard coral. We commonly call this one “bubble coral” because it features round, pearl-shaped bubbles that look just like fish eggs, which is what most divers think it is.
Plerogyra can make two types of bubbles. One is a smooth, grape-shaped bubble, and the other is a pearl-shaped bubble. Both are the same species they just feature different-shaped bubbles. The skeleton of this coral has sharp blades below the inflated bubbles, so it’s important to never touch a bubble coral as you can easily tear the bubbles, exposing it to infection.
Euphyllia corals have long, flowing polyps that feature an anchor-shaped tip. These corals can have either a branching skeleton or a long, meandering skeleton. During the day it’s easy to mistake these for soft corals, but at night the skeleton looks like a thick maze since the polyp retracts inside. These corals are most often green, but you can also find them in orange, yellow and shades of gray. They sometimes feature a mix of color and really lucky divers might even spot a deep maroon Euphyllia.
Beautiful Goniopora is sometimes quite abundant in muck habitats. The common name for Gonipora is flowerpot corals because the long tentacles look just like little flowers. The skeleton can be one round ball that sits on the sand, or it can grow into thick branches with rounded tips, depending on the species.
You can find Goniopora coral in practically any color imaginable. Some of the most beautiful are purple with blue centers or bright orange with yellow centers.
Catalyphyllia is a flowing, elegant coral that lives in muck habitats. The skeleton is meandering and not connected to anything at the bottom, it simply rests in the sand. Most divers easily mistake this coral for a sea anemone but looking closely at the center of the tentacles reveals that this coral has multiple mouths. A sea anemone would only have one.
For a real challenge, look for the Catalyphyllia coral with purple or blue-tip tentacles. This zebra-striped purple-tip coral resides in the muck habitats around Lembeh Strait.