Anemones

A close up of jewel anemones (Corynactis viridis). Photo by Dr. Alex Mustard, more can be found at www.amustard.com

Domain: Eukarya
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Order: Actiniaria

I have often heard people refer to sea anemones as flowers or sea flowers, and I always wondered why. Apparently, these organisms gained their common name because their bright colors reminded people of the terrestrial anemone flower.

It makes sense why people would consider sea anemones as flowers. Sea anemones don’t appear to move, they’re brightly colored, and their tentacles can resemble petals. However, like their coral and jellyfish cousins, sea anemones are animals.

A sea anemone is a single large polyp that lacks any skeletal structure and contains stinging cells called nematocysts. They have cylindrical bodies that are attached to hard substrates by their adhesive pedal disk, or foot. Its mouth, or oral disk, rests near the top of the body and is surrounded by tentacles, which they can retract into their body when feeling threatened.

Sea anemones come in all shapes, sizes, and colors. There are over 1000 species that range from half an inch wide to over 6 feet wide. They appear in various shades of blue, green, yellow, and red. Many species are more than one color or shade; often, the tentacles can be a different color than the body. Species in warm tropical waters are often larger and more colorful than sea anemones found in deeper, colder water.

Sea anemones are found in every ocean. They can be found at various depths, from shallow water to over 3000 meters deep in the ocean. They inhabit various crevices of coral reefs, rocky substrates, and sea walls. Some have been recorded on the backs of sea turtles.

Sea anemones are carnivores. They feed on planktonic organisms, crustaceans, small fish, and occasionally mollusks and sea urchins. The tentacles of sea anemones are used in defense and for capturing food. These stinging tentacles are touch sensitive. When potential prey brush up against the tentacles, harpoon-like filaments, called nematocysts, are launched at the prey. The nematocyst hooks into the prey and releases a neurotoxin that paralyzes the creature, then the tentacles pull the prey to the oral disk to be consumed.

Some organisms are immune to the stinging tentacles and coexist with various species of sea anemones.

Many people are aware of clownfish and their mutualistic relationship with sea anemones. Clownfish have a unique adaptation that allow them to live within the tentacles of the anemone. The sea anemone provides protection for the clownfish, and the clownfish will keep the anemone clean and lure potential prey to the anemone.

Other symbiotic relationships with sea anemones include various small crustaceans and zooxanthellae.

The stinging tentacles of the sea anemone don’t protect it from every organism. Various species of starfish, sea slugs, eels, and some species of fish prey upon anemones. Occasionally, sea turtles have been recorded munching on sea anemones when given the chance.

I don’t believe there is a Cnidarian that I don’t find fascinating. At the aquarium where I volunteer, there’s an exhibit that shows how some sea anemones rely on wave action to supply them with food. It’s one of my favorite exhibits because it’s so bright and colorful, and I find it relaxing to watch. Every few minutes, the exhibit simulates incoming waves, and you can watch the water whooshing down toward the sea anemones.

Sources and links:
Reef Creature Identification Florida Caribbean Bahamas 3rd edition by Paul Humann, Ned DeLoach and Les Wilk
Ocean: A Visual Encyclopedia (Smithsonian) by John Woodward
https://www.nationalgeographic.com/animals/invertebrates/group/sea-anemones/
https://www.britannica.com/animal/sea-anemone
https://aqua.org/Experience/Animal-Index/anemones
https://animals.net/sea-anemone/