The most familiar Cnidarian are probably hard corals! Each hard coral is a colony of tiny animals called polyps. Each polyp produces a hard skeleton. What you see as a hard coral is the joined up skeletons of countless tiny polyps. When the polyps extend their tentacles, the colony can appear furry.
mass coral spawning. When many corals release eggs and sperm at the same time.
sea fans! These beautiful delicate creatures are often mistaken for plants. A sea fan is also a colony of tiny polyps. When the polyps are extended, the colony has a fluffy appearance. Gorgonian colonies usually take on branching forms, but the branching is only along one plane (i.e., most are not bushy).
Flowery soft corals are also colonies of tiny polyps.
zoanthids are not colonial, the polyps do grow very close to one another.
Sea anemones are single polyps and are not colonial. Carpet anemones are flat and often have a pair of shrimps that are adapted to live safely from the anemone's stings.
Cerianthids are NOT true sea anemones. They have a ring of longer outer tentacles with an inner ring of shorter tentacles.
Did you make a cnidarian plushie? I would love it if you could share a photo of it!
This article is written for Celebrating Singapore Shores as part of International Year of the Reef 2018.