It hates lamps and flashlights, but doesn't mind the flash, and has built a new tunnel right up against the glass, so I've managed to get a few photos.
|Under the sand, there doesn't seem to be a sheath. The two tentacles (or palps) go up through the little sand tube. (The red tentacles are an observant grainy hand hermit, and what looks like his one big eye is a limpet on the glass.)|
Seen up close, this is a polychaete, a bristle worm. Along both sides, it has a series of little paddle feet (parapodia, meaning "beside feet"), here sprouting out of the centre of each ringed section. These may end in bristles; I zoomed 'way in, but I couldn't be sure.
|The parapodia are clearer here.|
If you look closely, you can see that its belly is to the left in the first photo, and to the right in this one. The worm is constantly moving inside its tunnel, swinging itself back and forth to enlarge the tunnel. The paddles operate in a series, so that it looks like waves moving downwards, more or less the same movement as a millipede walking, but from front to back. (The millipede looks as if the feet were moving back to front. They aren't.) And except that the worm stays in place, unless it's disturbed, in which case it retracts deep into the tunnel, shrinking down its entire length instantly.
|A closer look at the sections and the parapodia.|
It quickly moves to a new location if a crab starts digging, but doesn't mind the hermits, who just wander about, picking up tidbids and nibbling on them. They don't touch the worm's tentacles; fair's fair.
From around the web: The worm's sheath is a coating of mucus. The sand would be stuck to that. Those papery tubes that turn up on the beach at low tide, an inch or two long, are remnants of these sheaths, left behind when the worm retracted for protection deep into the sand. Waves or animals rip them off, but no-one is harmed; the worm makes himself a new one. Overnight, as this one did the other day.
Buzz says, "Palps extending from tube remove waste from tube.
(The worm) feeds using cilia to produce water current and captures food with mucus balls.
As the worm grows, the tube will probably lengthen; we see them on the beach, up to about 4 inches long. The tube, not the worm.)
Long ago, we found a bamboo worm dying on Crescent Beach, this one identified tentatively* as Axiothella rubiocinta, the Red-banded bamboo worm. It was about 6 inches long.
A. rubiocinta does not have the two tentacles, and it has exactly 22 segments. I counted the ones I could see on mine; there are 25 or 26 visible. They make sand tubes, larger that Spio's, and often live in communities containing both species.
|Bamboo worm, Crescent Beach|
|Worm, Campbell River|
*"Tentatively". All my id's are tentative. Give me another 20 years or so to learn. Meanwhile, corrections are appreciated.