Friday, March 04, 2011

Behind the red door

On a sunny morning, at low tide, walk down a rocky beach picking up bits of seaweed, old clamshells and mussels, bits of rock. Chances are, you've picked up a few, or many, dwarf calcareous tubeworms, tiny white coils of calcium carbonate catching the sunlight. They're beautiful, so perfectly round, so sparkly, but that's about the limit of what you will see on that mussel in your hand. It lies inert, just a coiled hard pipe.

I tend to notice them, then turn my attention to something more intriguing.

Several tubeworms. But I was looking at the bryozoans and sponges. And is that a nudibranch?

The trouble is, to really see one, you have to find it alive, unafraid, and underwater. And you need a lens; they are too small to see more than a speck of red, even while they're feeding. And you need the light in the right place. So when I noticed one glued to the tip of a limpet cruising the eelgrass in my tank, and close to the glass, to boot, I ran for the camera and my home-made lens.

Dwarf tubeworm on limpet on eelgrass, about 1/2 inch wide (the eelgrass, that is).

There are several species of these calcareous tubeworms in BC waters*, virtually indistinguishable from each other without close study. Some prefer to settle on seaweeds, others choose rocks or shells; some form large communities.

The tube is white, sometimes thin enough to show the orange-red worm inside. Feeding, they extend a crown of red tentacles from the mouth of the tube. Startled (and your shadow will do the trick), they disappear inside, and the only sign of occupancy is the red trapdoor, or operculum, that they shut tight against predators.

The trapdoor has other uses. The worm has both male and female segments; once she/he has fertilized the eggs, the door becomes a brood chamber. Sometimes, depending on the species, the chamber is like a cup; sometimes it's more like a helmet.

Another species characteristic is the direction of the spiral. Going from the center outwards, this worm coils counter-clockwise. Others follow the clock.

A closer view. Trapdoor in front, crown of tentacles behind. The tube is old and stained, and has been banged about; it's broken in several places. The worm shows red through one hole, but can't be seen in the central coils.

Responding to my shadow. He's hidden inside, and the door is fast shut.

I found another limpet/worm combination on some sea lettuce. This one's quite a bit smaller.

A newer tube, cleaner and less chipped. Also counter-clockwise.

There are a few astoundingly gorgeous photos of similar worms from California, a much larger species, but with the same colours and structures, on Flickr, in John Albers-Mead's photostream. Look at this one!

*They can be found in many other locations, in a wide range of latitudes.


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