Marine invert sighting of the week

ETA: Thanks to the wonders of social networking, the ID of the worm is now in question. Without the animal I don't want to say anything for sure, but it may in fact be from a different polychaete annelid family (Onuphidae).

The title of this post is actually a misnomer, because I never saw the animal in question. I was collecting snails at a new location yesterday. The beach looked like this:

Beach covered with worm tubes.

The silty sand was being held together by dozens of large tubes. Tubes on a beach are not new to me. Many polychaete worms (distant relatives of the familar earthworm) make tubes out of sand or other materials on the beach. These animals live in their tubes, pumping food and oxygen down into the sediment to well below the level where such resources are normally found. The tubes also add structure to an otherwise unstructured area, and can change erosion and other dynamics of the beach quite drastically.

Normally the tubes I see are small, just a couple of centimeters above the sand. These were big honking tubes, made of a parchmenty substance with lots of pebbles and bits of shell attached.

Worm tube, with hand for scale.

It took me a little while, but eventually I realized that these tubes must belong to a group of worms that we showed our students in Invertebrate Zoology this year. I didn't have a shovel, so I wasn't able to uncover these massive tubes and check for sure. But I was in the right area, and the tubes look right, so I'm confident that I can claim to have seen this guy:

Chaetopterus spp. Photo from Wikipedia.

 Man, these worms are bizarre looking, are they not? The head end is at the top in the photo above. Each of the different segments has evolved to specialize on a different task. Some pump water through the burrow, some aid in various parts of the feeding of the organism (they feed using a mucus net to filter particles from the water).

For me, invert-lover that I am, it was very exciting to find and identify a specimen that I had previously only seen in the classroom. Plus, I found what I need for my research, so it was a good morning all around.