Most of the bristle or polychaete worms discussed in this month's column are small members of the "clean up" crew, a group of animals that specialize in "getting rid of the evidence." Sometimes, as the following piece of doggerel describes, they have the task of getting rid of dead meat, among other things…

Well, maybe not quite like that; few worms can play pinochle… poker, maybe; pinochle, never. Still, some worms, particularly the fireworms, are scavengers on carrion. Others however are predatory and still others are detritivores, specialized to eat particulate organic material of various origins.

Before describing the worms themselves, I would like to discuss the role they play in the "natural history" of a reef aquarium. Most of these animals live within various components of the substrate, either the unconsolidated substrate such as sand or crushed coral, or the rocks. If they live in the rocks, they often live in holes or burrows generally excavated by some other organisms, although a few worms may be capable of excavating their own burrows. Those worms that live in the sediments may burrow through the sediments leaving no trace. Alternatively, they may exist in tubes or burrows that may be either permanent or quite temporary.

The vast majority of polychaete worms are tube-dwellers, living in some sort of burrow, and often that burrow is considerably longer than the worm itself. Generally, these tubes are at least stabilized by a mucous lining secreted by the worm. Such a lining is smooth and non-abrasive and allows the worm to move freely within the tube. Many tubes are strengthened even more fully by the presence of embedded sand grains or other particulate material. In some cases, the sand grains are cemented together into hard structures, and masses of these tubes may even form reefs. Sabellarid worm reefs in the Northeastern Pacific as well as in some tropical areas may be several hundred feet long, and over one hundred feet in height. The "ultimate" in "designer" tubes are secreted by some species of feather duster worms, in the group known as the Family Serpulidae. Serpulids secrete calcareous tubes that are typically white and quite rugged. In many cases, knowing the type of tube the worm secretes can be of assistance in its identification.

Most of these kinds of worms in aquaria are quite small, generally less than an inch in length, and their normal aquarium habitat is more like a natural habitat than perhaps any other reef aquarium biological component. Aquarists typically pay these small worms no heed, and they largely exist independently of the aquarists' efforts to manage their tanks. The sediments or rock rubble habitats have their own microhabitats, and food webs, that mimic the natural world quite well.

The small polychaetes that live in the substrate form a diverse group, one that is probably different in detail in each aquarium, but also one that has general similarities in each system. These worms act to break down, utilize, and mobilize organic materials. In doing so, they move excess chemical energy and biological nutrients through the system, eventually allowing for the export of these excess materials. The food, or energy and materials, that they eat goes to make more worms and, in the process, some of the material is released as waste material, gases, or soluble nutrients which may be either exported from the system or recycled even further.

All feeding types are found in this group of worms; there are predators, herbivores, and omnivores, as well as animals specialized to eat detritus and sediments. In natural marine ecosystems, any potential food item has several specific types of worms specialized to eat it. Many of these worms have found their way into aquaria, so the array of small worms that may be found in our systems is quite large. I will try to deal with some of the more common ones.

I have grouped the types of worms into functionally similar groupings that you may use to identify them. I will briefly discuss each worm type, telling a bit about them. More detailed information may be found by either searching for web sites or by going to a library and using print references. Although there are some larger species in each of these groups, with the exception of the feather-duster worms, most of the animals likely to be encountered will be tiny. You will need a good magnifying glass, hand lens, or microscope to be able to examine them in enough detail to identify them.

Permanent tube-dwelling worms are exemplified by the feather dusters, one group of polychaete or bristle worms welcomed by most aquarists. The feather duster worms are the only worms discussed in this month's column that are likely to be intentionally added to a reef aquarium. These worms construct a permanent burrow that they will never willingly leave, albeit they may bail out if environmental conditions get quite bad. As these worms never leave their burrow, they don't really have much in the way of locomotory capabilities. Once they start to secrete their tube, their options for movement are decidedly limited. In effect, they can move toward the opening of the tube or they can move away from it. Generally, the tubes are open only at one end. The worm's head faces toward the open end. As the worm isn't really ever going to go anywhere, it makes no sense for it to have a lot of purely sensory tentacles and structures originating from the head. Likewise, if the worm is removed from the tube, the parapodia or appendages down the side of the body will be seen to be quite reduced. The worm can move up and down in the tube efficiently and, in some cases, very rapidly, but that is really all that it can do.

These worms are unable to go out and hunt for food. But, they really don't have to go out for dinner since it comes to them. One of the characteristics of most shallow water marine environments is the present of a great amount of small particulate organic material in the water. Most of this stuff is edible. In fact, some of it is quite nutritious and these worms are all well adapted to capture it. The heads on representatives of all of these families have been modified as suspension-feeding organs. These modifications vary in detail amongst the four families constituting this assemblage of worms, but in most of them, there is an array of tentacles that extend from the head out into the water. In many of these worms, the tentacles are branched, with smaller sub-branches being found extending from the main tentacle. These branches are arranged in a "pinnate" manner; in other words, with each of the smaller branches being found opposite another small branch on the other side of the main tentacle axis. This branching pattern gives the tentacles the appearance of a bird's feather, and the whole array of feeding tentacles can look like a miniature version of a feather duster. This appearance has given the entire group the name of "Feather-Duster Worms".

Figure 1. Spirorbis on a rock. The small, coiled white shells are characteristic of this type of worm.

Feather-duster worms are not all alike, yet there are sufficient similarities for most taxonomic authorities to put them in the same general group. They are all robust worms, rather broad for their length. Inside the tube the body is regionated. There is a head region, defined by the feeding tentacles called "radioles." Below the head is a region called the "thorax." The major function of this region appears to be that of providing locomotion up and down in the tube. Although the body appendages are reduced from what is seen in free-living worms, they still bear large and evident bristles, which are mostly modified into rows of small gripping hooks.

As far as aquarists are concerned, the worms differ primarily in the construction of their tubes and their sizes. The distinguishing characteristics of feather-duster worms, by family, are:

• Family Spirorbidae: small calcareous tubes, tube arranged in spiral on aquarium rocks or wall; the coiled tube is less than one fourth of inch across. They are common hitchhikers into marine aquaria. The most common genus found in reef aquaria is likely Spirorbis. They reproduce well in aquaria and sometimes become very abundant.

• Family Serpulidae: commonly known as "hard-tube" or "calcareous" tube feather-duster worms, these worms have calcareous tubes. The tubes are not in a spiral pattern, but elongated and linear. These may be quite large worms with the tubes being up to about an inch in diameter and over a foot long. Smaller individuals, however, are much more common. Some serpulids, such as the "Christmas Tree Worms," burrow in living coral heads. Smaller worms with exposed tubes are common on reef rubble and on loose rocks. Serpulids often have a hard plug or operculum to fit into the ends of the tubes. Some serpulids, such as the Christmas-tree worms, Spirobranchus gigantea, and the large hard-tubed, feather dusters in the genus Bispira, are quite attractive and are often purchased by reef aquarists.

• Family Sabellidae: worms in this family are the "true" feather duster worms. They secrete a proteinaceous tube that has been called "parchment-like" in consistency. While most of the sabellids are small, about the diameter of a thick pencil lead, some of them do get quite large; feather duster worms in excess of two feet long with a dense tentacle crown four or more inches in diameter are known from some temperate regions. Larger feather dusters such as Sabellastarte magnifica are commonly sold for the hobby, but smaller species also appear frequently in with some live rock.

• The Family Sabellaridae: these worms construct their tubes out of cemented sand grains. Even though this sounds like an impermanent type of structure, in practice, these are the most rugged of all worm tubes. These worms are gregarious and preferentially settle and metamorphose out of the plankton on to tubes of their same species. These can result in huge reefs with an outer husk of living worms on their outer surfaces. Sabellarids are not commonly found in reef aquaria, but occasionally are imported as hitchhikers on live rock.

Figure 2. Apomatus, a temperate serpulid worm. Note the calcareous tubes, including the fractured tube to the upper left. The operculum, or plug for the tube is the spherical object above the crown of feeding tentacles. The tube to the upper right is from a smaller species of serpulid.

Figure 3. Smalcina tribranciata, a small serpulid that is gregarious and forms masses of intertwined, twisted tubes. These individual tubes are about 1/50th of an inch across; the entire clump of worms pictured here is about a third of an inch long.

Figure 4. Spirobranchus gigantea in a Porites colony. The white scars are due to parrotfish bites. This serpulid worm has a calcareous tube that extends into the coral head. The operculum that plugs the tube is the funnel-shaped object at the bottom of each feeding crown.

Figure 5. A common small sabellid, possibly an individual in a species of Sabella, photographed through the wall of a reef tank. Note the non-calcareous nature of the tube, with the worm visible inside it. The dark spots on the tentacles are eyespots and allow the worm to rapidly withdraw should the illumination rapidly change, such as when a fish approaches. The tentacle crown is about half an inch across.

Figure 6. Eudistylia vancouverense. This temperate sabellid has a tentacle crown about six inches across, and the tubes may extend over three feet out of the sediments, and several feet into them. These worms form patch reefs that persist for years. The worm tubes may become covered with barnacles and mussels.

Figure 7. Sabellaria cementarium, a feather duster worm with a tube formed of sand grains cemented together. The tentacle crowns are about half an inch across.

Figure 8. A portion of a reef formed by Sabellaria cementarium, the species illustrated in Figure 7. The various worms and some bryozoan colonies are indicated. This reef was over 300 feet long, 100 feet wide and extended in depth from 25 feet to about 125 feet.

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.

Figure 9. A chaetopterid worm feeding by extending its two tentacles from its tube. Spionid worms would look much the same and could not be distinguished without removing the worm from the tube.

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.

Figure 10. Phyllochaetopterus sp. Left: Animal in the tube with its tentacles extended. Right: Animal removed from the tube. Note the small regionated body and large tentacles.

Several kinds of worms with more than two tentacles are common on natural reefs, but only two types of these occur frequently in marine reef aquaria. These are the worms in the Families Terebellidae and Cirratulidae, represented in aquaria by spaghetti and hair worms, respectively. These two types of worms are easy to distinguish; the spaghetti worms live in a well formed, permanent tube and while they may move in the tube, those tubes are typically fixed in position and immobile. The hair worms are found living in the sediments, or occasionally on the rocks, and while never especially speedy, they are capable of moving from place to place. I have written a detailed discussion about these types of worms and interested readers should go to that column for more information.

There have been representatives from quite a number of more actively mobile worms found in aquaria, but only those from two families seem to become either very common or appear to be distributed widely. Representatives of these two groups, the Family Syllidae and the Family Dorvilleidae, have been found in a number of aquaria from around the world. They are not easy for the average aquarist either to identify or distinguish between. In fact, even for seasoned polychaetologists, the syllids are difficult to work with, and identification is difficult; there are a vast number of species and their biological attributes are very poorly known. Dorvilleids are also poorly known biologically, however, they are fewer in number and less diverse than are the syllids.

Syllid polychaetes have three antennae. One antenna is located on the mid-line at the top of the head, the other two are each located some distance laterally to the center one. These worms have a strong muscular proventriculus, or gizzard; presumably it is used to mash and grind food. The proventriculus is a good character to use in identifying an unknown worm as a syllid as they all have it. The proventriculus is quite evident as a dark structure found around the front part of the gut when light is shined through the body. There may, or may not, be slender tentacles arising from the parapodia on each side of the body. If there are such tentacles, they often will have the appearance of a string of beads. Much of the taxonomy of the syllids concerns the shapes and distributions of the various types of bristles. As these shapes may only be seen clearly with magnifications of 1000x or more, this level of identification is well out of our league. Nonetheless, if you have a small slender worm with an evident gizzard, is likely a syllid. If it has beaded tentacles you may be sure of your identification, as such tentacles are not likely to be found on any other polychaetes. Syllids are generally considered to be predatory, but many species symbiotically live with other animals, such as sponges and soft corals. Whether or not these symbioses are commensalistic, mutualistic, or parasitic is unclear. Free-living syllids are generally regarded as being predatory, mostly on other worms.

Figure 11. A juvenile syllid collected from my aquarium. Note the tiny antenna in the middle at the front end (on the right). The gizzard and the beaded tentacles are labeled. The worm was about 1/25th of an inch long.

Dorvilleid polychaetes are related to the big eunicid worms discussed last month, but instead of five antennae they have only four. As with the rest of the eunicids, dorvilleids have jaws. They are typically short-bodied worms with a blunt front end, and the appearance of a rounded front end with four small antennae arising from it is quite characteristic of this family and may be regarded as distinctive. However, these are quite small worms, only a few millimeters long, and this small size makes the characters difficult to discern. If you can shine a light through such a small worm and see the small black jaws internally, you can be reasonably sure you are dealing with a dorvilleid. These animals have been characterized as predatory, but some aquarium forms have been seen to use their jaws to cut off pieces of algae.

Figure 12. A dorvilleid worm collected from my aquarium. Note the rounded "nose," black jaws, four antennae (one on the right side is obscured) and the paired eyes. This animal was about one tenth of an inch long.

There are many other types of bristle worms found in marine aquaria, and I am sure the number of reported types will increase in the future as people start to use less toxic water mixes, and as shipping of live rock and live sand gets less traumatic for the animals in them. In this series of columns, I have given both the characteristics for identification, and some descriptions of the common polychaetes found in reef aquaria. Almost all of them are either beneficial or, at least, harmless, and should not be looked upon with dread and foreboding by any aquarist. They are supremely well-adapted for their way of life; that is as a crawling animal able to exploit small spaces between and among rocks.

For Everything You Wanted To Know About Worms But Were Afraid To Ask:

http://biodiversity.uno.edu/~worms/annelid.html

Some Useful References:

Fauchald, K. 1977. The polychaete worms; definitions and keys to the orders, families, and genera. Science Series 28. Natural History Museum of Los Angeles County. Los Angeles, CA. 188 pp.

Fauchald, K. and P. Jumars. 1979. The diet of worms: a study of polychaete feeding guilds. Oceanography and Marine Biology Annual Review. 17:193-284.

Kozloff, E. N. 1990. Invertebrates. Saunders College Publishing. Philadelphia. 866 pp.

Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. Saunders College Publishing. Philadelphia. 1056 pp.