This week, when yards are all aglow with holiday lights, there is another unusual light to be found in the intertidal. It’s a strange little worm that has a hidden power to glow in the dark. While many glowing ocean creatures are found in the dark depths, these are found in the shallow waters close to shore. They are pretty small, not often getting over a few inches in length, and easy to miss when they aren’t aglow, but these little segmented worms are a lucky find.
Guenola Lefeuvre photo
A friend recently found one in a tidepool in Cape Elizabeth crawling on a piece of seaweed. With a little help from some scientists at the University of New Hampshire, we were able to identify it as Harmothoe imbricata. Imbricata means “overlapping like shingles” which is an apt description for its scaly body. Harmathoe was a Greek Amazonian warrior. Perhaps the fact that this little worm glows is a reflection of rare Amazonian power. Or, perhaps it refers more to its close relative, the bearded fireworm, that can impart an unpleasant sting with its bristles if touched by bare skin.
Both species belong to a group of animals known as scale worms or polynoids. These names refer to the fact that they have multiple segments or scales. Think of them as underwater roly poly bugs. Like a roly poly, scale worms have an array of little appendages that help them to move. There is a little muscle under each bristle called a parapodia, which means “a near foot.” That’s because it controls the little bristles, or setae, that help the scale worm to move. These bristles are like the ones that have tiny stingers in the bearded fireworm, but those bristles are designed more for support than movement. The parapodia and bristles help the worm to hang on to things like the seaweed this one was found on, and to crawl.
Despite their size, scale worms are fierce predators. They can feed on each other as well as small snails and other invertebrates, using a proboscis, or sharp tongue that has something like teeth on the end to consume its prey. They can also eat a variety of plankton and seaweed. When it comes to what eats them, one of the reasons scale worms glow is to deter predators. They can toss off their glowing scales as a distraction as they escape and hide.
The ocean is full of glow-in-dark creatures from those as tiny as plankton to those as giant as whale sharks. Often, they use the power of glowing to distract predators or to light up the dark parts of the ocean. It is an amazing chemical reaction that happens in their body much like the mixing of two chemicals inside a glow stick when you crack the little tube hidden inside.
In the season of long nights and short days, it might seem that the only lights are those of inflatable Santas and snow globes. And while it might seem like the ocean is a dark, inaccessible place, there is light in the ocean. Few of the sea’s glowing creatures are both large enough to see with the naked eye and live in places like tidepools where we can see them from shore, but this little worm is a treasure to be found along our coast.
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