Sea anemones, like the one pictured above in a tide pool on the Oregon coast, at first glance seem like flowers from an alien world. The fact that some land flowers are also called anemones adds to the confusion. (The word anemone is from Latinized Greek, meaning 'daughter of the wind', and a common name for land anemones is 'windflower.')
Photo: giant green anemone, partially closed, in tide pool at Yaquina Head on the Oregon coast. By E. Sherr.
Looks can be deceiving. Sea anemones are certainly not plants. Rather, these relatives of jellyfish and corals are large single polyps with a flat disc on the bottom that they use to hold tight to surfaces. Their waving tentacles have stinging cells, nematocysts, as do jellyfish. When a small fish or crustacean brushes by, the tentacles deliver a numbing barrage of toxins, and the stunned prey is grabbed and delivered to the mouth in the middle of the tentacle crown.
Most sea anemones are found in hard bottom habitats: rocky shores, coral reefs, or subsurface outcrops such as Gray's Reef off the Georgia coast. Among the jumble of marine life that grows on wharf pilings is a pale, translucent polyp up to one and a half inches long. This is the ghost anemone, Diadumene leucolena. But there are anemones on the Georgia coast that are more mobile than the ones stuck to rocks or docks.
Beachcombers may come across a tan, striped anemone, Calliactis tricolor, which attaches itself to shells inhabited by hermit crabs. Out of water, the hermit crab anemone is just an elastic, glistening lump. Restored to a tidal pool, the anemone will slowly expand its crown of tentacles, revealing delicate orange, red, or yellow colors. The anemones get a free ride and leftovers from the hermit's meals, while the hermit is protected by the anemones' stinging tentacles.
Hermit crab with three symbiotic anemones, Calliactis sp. ,attached to its shell. Dardanus pedunculatus (Hermit crab)" by Nhobgood Nick Hobgood - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons -
The bodies of other coastal anemones end in a round digging organ instead of an attachment disc. These burrowing anemones, one to three inches long, tunnel under sandy sediments, expanding their feeding tentacles into water currents just above the surface.
The South African burrowing anemone, Ceriantheopsis austroafricanus in 24m of water in False Bay, off Cape Town, South Africa.
"Burrowing anemone 0796" by Seascapeza - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons -
Surprisingly, a miniature cousin of burrowing anemones lives in salt marsh mud. The half-inch-long starlet sea anemone, Nematostella vectensis, extrudes its tentacles from the surface of marsh sediments to ensnare fly larvae and benthic copepods. These tiny, pale anemones are a food resource for grass shrimp that come onto the marsh at high tide to feed. They are also useful to scientists. It turns out that the starlet anemone is easy to grow in the laboratory. Because anemones are related to jellyfish, one of the simplest and first forms of multicellular life to appear in the fossil record, molecular geneticists have been analyzing the genome of this polyp for clues to the evolution of animals.
Tiny starlet anemone in a laboratory dish. "Nematostella vectensis"
by Cymothoa exigua - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons -