Head to head
Sea Anemone vs Coral
A coral polyp and a sea anemone are so alike that a single coral polyp is often described as a miniature anemone. They are close relatives in the same class, and the differences come down to skeletons, colonies, and mobility.
| Sea Anemone | Coral | |
|---|---|---|
| Class | Anthozoa (order Actiniaria) | Anthozoa (order Scleractinia and others) |
| Skeleton | None; entirely soft-bodied | Stony corals build a hard limestone skeleton |
| Body | One large solitary polyp | A colony of many small connected polyps |
| Reef building | No | Stony corals build reefs over generations |
| Mobility | Can crawl, somersault, or swim to escape | Fixed in place for life |
| Size of a polyp | Up to 30 cm or more across | Usually 1 to 3 mm across |
| Symbiotic algae | In many species | In most reef-building species |
| Lifespan | Decades; some past 100 years | A colony can persist for centuries |
Sea Anemone vs Coral: common questions
Is a coral polyp the same as a sea anemone?
Structurally it is almost identical, which is why a coral polyp is often called a miniature anemone. Both are anthozoans, built as a hollow cylinder with a mouth ringed by stinging tentacles and no jellyfish stage in the life cycle. The differences are what the polyp does. A stony coral polyp secretes a hard limestone cup around its base and lives as one unit in a connected colony that builds a reef, and each polyp is typically only a millimetre or two across. A sea anemone polyp is solitary, often large, builds no skeleton, and can move. So a coral polyp and an anemone are close cousins doing very different things.
Which one builds coral reefs?
Corals, specifically the reef-building or stony corals in the order Scleractinia. Each polyp lays down a calcium carbonate skeleton beneath itself, the polyps of a colony build a shared structure, and as old colonies die and new ones grow on top, the skeletons accumulate over thousands of years into a reef. Sea anemones contribute nothing to reef structure because they have no skeleton, although they live on and around reefs. The giant carpet and magnificent anemones that host clownfish, for instance, sit on the reef but are not part of its framework.
Can a sea anemone move and a coral cannot?
Yes, that is one of the clearest practical differences. An adult sea anemone, despite usually staying in one spot, can detach its base and slowly glide across a surface, tumble end over end, curl up and let the current carry it, or in some species actively swim by thrashing, mainly to escape a predatory sea star or an aggressive neighbour. A coral colony is cemented in place by its own skeleton and cannot relocate; only its free-swimming larvae move, drifting in the plankton before settling and founding a new colony. Both, of course, spend most of their time stationary.