More than Meets the Eye
By Dr. Scott France
Much of the canyon bottom that we traverse is covered in mud and sand, with occasional rocks and cobbles scattered about. On these soft bottoms we have encountered many sea anemones, close relatives of corals. We’ve seen several different species of anemones in a variety of sizes and colors: purple, pink, orange, snow white, but all with the basic sea anemone shape. To picture the sea anemone, think of one of those take-out cups with a lid that has an opening for a straw: the cup is the anemone body, the lip of the cup is where tentacles arise, the straw opening is the mouth, and the inside of the cup is the stomach; the flat bottom of the cup is used by anemones to hold tightly to whatever surface they are living on – they can even live hanging upside down. Anemones will eat almost anything they can get their tentacles on that they can fit in their mouth: from zooplankton, shrimp and clams, to fish. After they have digested as much as they can, the remains are popped back out through the mouth: after all, it’s the only opening into or out of the stomach (just like the cup with the straw hole)!
Among these sea anemones is another animal that at first glance appears to be just another sea anemone. But this one is different: it is living in a slimy, soft tube that protrudes above the bottom, and, if you look closely, it has two rings of tentacles, long ones around the edge of the “cup” and shorter ones directly surrounding the mouth (the straw hole). This animal is a tube anemone (formal name “cerianthid anemone”), and it builds the tube it lives in using mucous, the surrounding mud, and special thread-like structures it fires from out of its cells to bind it all together. The tube can extend deep into the mud, much longer than the tube anemone itself, so that when disturbed, the cerianthid can withdraw deep into its burrow for safety. The inside of the tube is extremely smooth and slimy – from all the mucous the cerianthid produces, allowing it to slide easily.
We collected one tube anemone that had more than 10 orange-colored anemones growing on the outside of the tube, as well as some glass sponges and other invertebrates. The ROV pilots were so surprised when, as they lifted the manipulator arm, the tube seemed to keep coming out of the bottom. “How long is this thing?” they exclaimed. In the ship’s lab I pulled off the anemones and sponges from the outside of the tube, and then carefully cut the tube open to reveal the cerianthid within. It was at least 10” long, and unlike sea anemones, had a pointed bottom instead of a flat one; this anemone does not live stuck to a surface! And even though it is a pretty big size, the cerianthid was much shorter than the tube. Several of us ran our fingers along the inside of the tube and marveled at the silky smoothness and cleanliness compared to the muddy exterior.
Sometimes things aren’t as simple as they appear; there is more than meets the eye, and for me that powers the excitement of exploration.