Frilled anemones are common in local waters

Look over the edge of almost any dock along the numerous inlets and harbors of the Gulf of Maine and you're likely to see a fairly good-sized anemone waving its frilly tentacles up at you. The frilled anemone (Metridium senile) is a fairly common large, showy anemone that likes to grow on wharf pilings and tide pools from the Arctic south to Delaware Bay. The range of colors of this species is quite large; white, orange, pink, red, grey or olive green. Unlike some other sea anemones, the frilled variety is a uniform color throughout — no streaking or banding. Their size can vary too, there are a number of varieties, some grow to 12 inches tall, others rarely exceed 1 inch in height. Their common name, "frilled anemone" (or plumose anemone), refers to the numerous, fine tentacles, which vary. The larger anemones can have as many as 1,000 tentacles arranged in convoluted folds, the smaller varieties often have only a couple hundred.

Anemones are in the Phylum Cnidaria, the same group as the jellyfish and corals. The name "cnidaria" comes from the Greek word "cnidos" for stinging nettle, referring to the stinging cells (called cnidocytes) that all members of this phylum possess. These stinging cells are used to capture prey. The cnidocytes contain little harpoons called nematocysts, which are coiled threads that, when triggered by touch or some other cue, are launched with such speed that they can puncture and inject a paralyzing neurotoxin into their prey. The toxin immobilizes the prey enabling the tentacles to draw the prey into the centrally-located mouth. Most Cnidarian nematocysts will not harm humans because the stinging threads cannot penetrate our thick skin. This is true of the frilled anemone; if you stick your finger into the midst of the tentacles they will retract and, if you're lucky, you'll be able to feel them stick to your skin.

Since I was a child I have loved the idea that that stickiness was the result of thousands, maybe millions, of tiny harpoons, and still have the (probably annoying to the anemone) habit of sticking my finger into every anemone I find to experience the thrill of that connection.

Sea anemones are classified as animals, not flowers, despite their name inspired by the terrestrial anemone flower. Recent research, however, indicates that they can, technically, be considered half plant and half animal. This study, published in the journal Genome Research, determined that even though the genes, on the DNA level, are very similar to other animals (like us humans), cnidarians use a plant-like system to control the expression of the "animal" genes. Cnidarians have been around a long time, over 600 million years; they are one of the earliest animal groups to evolve. It is believed that since they branched off so early, they retained the plant-like gene regulation from some common ancestor with plants!

It is really amazing what you can see hanging off of the edge of a dock. On my town dock the parts that haven't been recently scraped look like a jungle; small hydroids, sea weeds, sponges and mussels form the lower canopy, with the giant frilled anemones playing the role of the biggest trees in the forest.

Sue Pike, a researcher and an environmental sciences and biology teacher at St. Thomas Aquinas High School, welcomes your ideas for future column topics. She may be reached at spike3116@gmail.com or via her blog, sp.stalux.org.