When I became a diver, worms were among the first reef creatures to attract my attention. More accurately, it was the exposed crowns of frilly gills of Christmas Tree Worms, Spirobranchus giganteus, that drew my eye—so colorful, so appealing, so utterly unwormlike, and to Anna’s and my unending irritation, gone in a flash whenever we swam too close.
While the worms’ long segmented bodies remain tucked away safe and sound inside strong calcareous tubes, their delicate crowns, vital for absorbing oxygen and gathering food, must deal with the rigors of a dangerous world outside. To avoid being eaten or damaged, the delicate spirals retract in an instant whenever suspicious shadows or extraneous water movements are detected. Think divers. For insurance, a trap door topped with a spike slams tightly shut behind the disappearing tentacles.
The lovely twin crowns are lined with tiny mucus-covered filaments, known as cilia. When currents are calm the cilia beat in waves sending oxygen-rich water, along with planktonic food and grit spinning down their spiraling tentacles leading to the mouth. The sand is sorted by size for later use as building material necessary for slowly extending the tubes to keep pace with the coral’s grown. If all goes as planned, worms can live for decades and grow to impressive lengths.
In the southern Caribbean, Yellownose Gobies often live on the same coral heads, or mooring blocks where Christmas Tree Worms make their homes. The gobies obtain the majority of their sustenance from picking parasites off client fishes. But it seems, at times, they can’t resist easy pickings at the expense of the worms. We have followed the bandits going from worm to worm somehow able to slip inside their open crowns to snap up ensnared bits of food without being detected.
Last year, Dr. Peter Wirtz shared his paper describing the behavior of a shrimp that steals food from a fan worm (closedly related the the Christmas Tree worm). The shrimp is practicing kleptoparasitism, that is, food stealing. Though we’ve yet to find any other documentation of the behavior we’ve observed, we’ve always believed the gobies are stealing food from the Christmas Tree worms, in other words, practicing kleptoparasitism. We wrote about it in 2014 in our Critter Hunt column in Scuba Diving magazine and created a short video that was shown on their site for a while. We’ve resurrected it and loaded it here: https://www.youtube.com/watch?v=tieQP218UME
Reference: Wittmann, K.J; Wirtz, P. (2017). Heteromysis sabelliphila sp. nov. (Mysida, Mysidae, Heteromysinae) in facultative association with sabellids from the Cape Verde Islands (subtropical N.E. Atlantic). Crustaceana. 90(2): 131-151.