Published July 9, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott
One of the joys of snorkeling or beach walking in Australia is finding marine animals new to me. It’s also frustrating because being on my sailboat, I often don’t have internet access or the right books on board to look up what I’ve found.
The creature that stumped me on my recent trip appeared on Whitehaven Beach during an extremely low tide. At first glance the thing looked like a line of white seashells tangled up in brown and green seaweed. But when a small wave rolled over the clump, it stayed in place, fixed to the spot.
Down the beach, a longer string of shells and seaweed appeared, then another and another, all streaming behind the receding water like glistening ornaments. Mermaid bracelets, I named them, because a few of the shells in the strands were the forams I wrote about called mermaid pennies (May 28).
I gently scooped sand from around one of the shell ropes and found it anchored a few inches down in the sand. I laid my strand above the break to examine it, and out from the end popped a pair of rust-colored antennae and behind them several fuzzy legs. I had found a bristle worm that collects shells. I’m home now, and, as usual, Google found my mystery worm first try, even with the lame search words “polychete (bristle worms’ scientific name) that makes tubes from shells.” My worm’s name is Diopatra (rhymes with Cleopatra). Members of this group live in self-made tubes of thin, paperlike material onto which they glue small shells, bits of algae and pieces of coral. The worm lives with the lower part of its tube body buried vertically in the sand and the top part drooping head-down over the seafloor, like a candy cane.
Diopatra shell jackets look decorative to us, but for these ambush predators they’re camouflage. When a small invertebrate wanders close to the worm-in-shell-clothing, the worm darts partially from its tube and grabs its prey with sharp jaws. When fresh meat is scarce, the worms eat dead plant and animal tissue.
Hawaii hosts at least two species of Diopatra. These little cross-species-dressers extend a third or more of their length from their tubes to feed in an arc around their anchored base. In some areas the worms’ dense presence between reef and beach stabilizes sand, preventing beach erosion.
These shell-dressed worms are exposed at very low tides, during which times the worms are in danger of drying out and/or getting eaten. I’ve not seen them before, but I’ll now be on the lookout.
I like the rather regal name Diopatra, and found it means “divine habitat” in Greek. For those of us who love walking beaches during low tide at first light, these worms are well named.