Worms With Two Tentacles - Harmless

Worms With Two Tentacles
There are a number of families of tube-dwelling worms that feed by extending two tentacles, often called palps, from their tube out into the water. They feed on small particulate material, and probably also absorb some dissolved organic matter. Representatives of only two of these families are likely to be found commonly in aquaria, however; these families are the Spionidae and the Chaetopteridae.

Although much more common than chaetopterids on real reefs, spionids are somewhat rare in reef tanks. They may make an appearance by extending their paired tentacles from a small hole in a piece of reef rock or perhaps a gorgonian or snail shell. They often extend their burrows into the non-living parts of corals and other animals with a calcareous shell. Many spionids are naturally found in sediments, but these particular worms do not seem to be particularly common in reef tanks. Without microscopic identification, it is hard to definitively identify spionids, but they may be distinguished from the following group by examining the worm's body. Spionids typically have a head, but lack other body regions; the front, middle, and back parts of the worms tend to look alike.

The similarity of the body regions is not the case with the chaetopterids, and at least one member of this family may be very abundant in reef tanks. This abundant worm is placed in the genus Phyllochaetopterus. Phyllochaetopterus individuals build a tube out of "hardened" mucus in which they cement sand grains. These tubes can be up to an inch or so in length and are about the diameter of a thin piece of pencil lead. They will be oriented vertically in the sediments or occasionally found filling pre-existing holes in rocks. The worms themselves are quite small, less than a quarter inch long; in fact, in most cases less than a tenth of an inch. Consequently, their typical tube provides them with quite a spacious home. The tentacles are often five to ten times the length of the rest of the worm, and when examined with a hand lens or good magnifying glass, the various regions of the worm may be seen to have distinctly different appearances.

Phyllochaetopterus is generally a benign member of the detritivore group found in reef tanks and they are pretty good scavengers; any particulate material that strikes their tentacles is pulled into the tube and eaten. However, they are gregarious and reproduce well in reef tanks. These two properties may, in time, cause some problems. The worms can form quite large mats with literally hundreds to thousands of tubes all cemented together. These mats quite efficiently exclude other worms from the area, and can seal off the sand bed surface. This, in turn, can cause the emigration of other animals out from under such a patch, which can result in the cementation of sediments under the patch and the failure of the sand bed biological filtration under the patch of worms. Such worm masses need to be periodically broken up or removed from the system, otherwise they may cause the complete failure of a deep sand bed. The reproduction and subsequent patch growth can occur with surprising speed. In a 60 gallon hex tank I once had, I introduced some of these worms and, within about three months, they had literally paved the sand bed surface with their tubes. I attempted to remove them all, and it was not an easy task.

Great write up

Khayman wrote:In a 60 gallon hex tank I once had, I introduced some of these worms and, within about three months, they had literally paved the sand bed surface with their tubes. I attempted to remove them all, and it was not an easy task.

Very informative write up. Thanks for taking the time to do it. I've never seen that many worms in a tank to complety cover the sandbed...must have been an interesting sight.