Descendants of the Cambrian: Sea Anemones

At first glance, anemones look like soft blossoms anchored to rock, their tentacles swaying with the tide. But look a little closer and you’ll see a skilled predator at work.

Each of those delicate arms is armed with nematocysts—microscopic, harpoon-like cells loaded with venom—ready to stun passing prey in a split second.

Sea anemones belong to the class Anthozoa, making them close relatives of corals and jellyfish. Unlike jellyfish, though, they’ve traded a life of drifting for one firmly planted in place, attaching themselves to reefs, rocks, and seafloors across the globe—from shallow tide pools to the deep sea.

Now, for us fossil folk, anemones present a bit of a challenge. They are soft-bodied, with no shells or bones to readily fossilise. So their presence in the fossil record is rare—more whisper than shout.

But we do have some beautiful clues.

Exceptional fossil sites, like the Burgess Shale in British Columbia—dating back over 508 million years—have preserved soft-bodied organisms in stunning detail. Here, we find anemone-like creatures that give us a glimpse into early anthozoan life during the Cambrian Explosion, a time when complex life was just beginning to flourish in Earth’s oceans.

We also find trace fossils—subtle impressions left in ancient seabeds. Circular marks and anchoring traces hint at where anemones once lived, even when their bodies themselves have long since vanished.

Modern anemones also host fascinating partnerships. Many live in symbiosis with algae, gaining energy from photosynthesis, while others form famous alliances—like clownfish weaving safely among their stinging tentacles.

So while they may seem delicate, anemones are ancient survivors—holding fast through mass extinctions and vast shifts in Earth’s history.