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Phylum Annelida -- Polychaetes,the bristleworms, Rob Toonen Aquarium.Net May 1997

Rob Toonen takes a good look at bristleworms in a reef, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

 Phylum Annelida -- Polychaetes,the bristleworms, Rob Toonen Aquarium.Net May 1997

Reefkeeper's Guide to Invertebrate Zoology: Part 8: " Phylum Annelida -- Polychaetes, "the bristleworms"

By Rob Toonen

Polychaetes are often referred to collectively as "bristleworms" although one must be careful about this term, because many people include/exclude different groups of worms when using it. For example, Mike Noreen uses the term "bristleworm" synonymously with "polychaete" in his Bristleworm fact sheet and mini FAQ , and many aquarists on the web seem to use the same convention. More commonly, however, invertebrate zoologists, if they use the term "bristleworm" at all, use it to refer specifically to the families in which the setae are large and obvious, such as the Nereids and Amphinomids (I'll describe all the commonly encountered families in a little detail in the next article). Some people take an even more narrow view of what constitutes a "bristleworm," however. For example, in his 1992 book, Martin Moe uses the term "bristleworm" as a synonym for only those species commonly called "fireworms" (Order Amphinomida , such as Hemodice carunculata ). The following is a quote from his book (pg. 454) "The bristleworms are not called fireworms just because of their bright orange and red colors. The fine, needle-like bristles are hollow and contain a potent venom. The stings caused by these worms feel like fire and last a long time." Given that the common name is nonspecific, and that different people mean different things when they say "bristleworm," I generally try to avoid using the word as a description or classification. That is why whenever I use the word, I enclose it in quotations. I have already seen several (and been involved in one) arguments over the dangers of "bristleworms" in a reef tank simply because one person uses the word as a synonym for the order Amphinomida, and the other for the class Polychaeta.

. Having just mentioned the dreaded fireworms, I should add that Morris Abbot and Haderlie (1980) report that some unfortunate people have required amputation of digits following encounters with certain species of fireworms. I have included this caution simply to indicate that there are some polychaetes for which a healthy respect is wise

Some of these worms are potentially quite toxic, and as such, if you discover a polychaete in your tank that looks like a "wooly-bear" caterpillar (like the Hermodice carunculata pictured here), please don't touch it with your bare hands ! I say this because, although there are really only a very few species with which you must be careful, if you are unfamiliar with the species and there is any potential for injury, why risk it -- a pair of rubber dishwashing gloves (PLEASE get a new pair for this purpose -- don't put the soapy pair for the kitchen into your tank!) is all that is necessary to protect yourself from a painful, and potentially dangerous injury. At the same time, I have yet to hear of anyone being hospitalized for treatment of a fireworm "sting" in relation to a reef aquarium. If you do happen to contact a fireworm, the long, hollow and brittle setae usually break off and embed themselves into your fingers. Once imbedded the setae cause inflammation, irritation, itching and numbness (usually associated with the toxin they contain, but also commonly due to infection).

Hermodice carunculata

If you happen to find yourself in the unfortunate situation of discovering first-hand why these animals are called fireworms, DO NOT rub the or scratch the injured area (you'll only make it worse, and possibly spread the irritation). Use a piece of masking or duct tape to carefully remove all the bristles you can, and then soak the affected area with rubbing alcohol, or better yet, a dilute ammonia solution (10 parts water to 1 part household ammonia).

Well, after that dire warning, I have to reiterate that the vast majority of polychaete species are at worst harmless to a reef tank, and at best beneficial in maintaining a healthy environment. The simple fact is that, along with a multitude of small arthropods, polychaetes are the marine equivalent of insects on land; there are some insects (like wasps) that you'd prefer to avoid, but for the most part we ignore "bugs" and many of them are beneficial. Polychaete worms are extremely abundant in all marine habitats, and I doubt there is ANY reef tank in existence that does NOT have polychaetes in it. Most reef habitats that have been censussed have on the order of 10 to 20,000 worms per square meter, and in some muddy-bottom areas with high organic input, densities of worms can reach over half a million per square meter.

Given those numbers, what do you think is the probability that your live rock came without any polychaete worms? OK, so you already have polychaetes in your tank. Now what?


Actually, I'm kidding, you probably shouldn't panic. The obvious question is: What sort of worms are they, and what made you notice them? There are probably a number of polychaetes that you have intentionally added to your tank, perhaps without even knowing they were polychaetes. The Christmas tree worm ( Spirobranchus giganteus , pictured above), along with several large "feather duster" ( Sabellastarte magnifica , or Hypiscomus elegans pictured here) or "duster cluster" ( Sabella melanostigma ) worms, for example, are often purchased for addition to reef tanks.

Feather duster worm Hypiscomus elegans

There are probably hundreds (if not hundreds of thousands) of worms living in your tank that you have not yet, and may never, notice. So what was it that made you sit up and pay attention to some animal and ponder if this is one of those "dreaded bristleworms" about which so much bandwidth is spent on the newsgroups?

In general the reaction at this point is a frantic post to the rec.aquaria.* newsgroups along the lines of: 1) "I saw some long centipede-like critter stick it's head out of a rock in my tank, and it freaked me out, should I take out the rock and bleach/boil it?"; 2) "I didn't think I had bristleworms, but last night I saw some worm swimming around my tank after I shut the lights off -- is it gonna kill my corals?"; 3) "Every once in a while, I see a big, ugly worm hanging out of a rock in my tank, is it dangerous?"; or 4) "There are small worms all over my soft coral -- what should I do to save it?" In general my response to such queries is "you should read Mike Noreen's mini FAQ ." Mike does a good job of explaining that the answers are 1) NO!, 2) Probably not, 3) Maybe, but probably not, and 4) Get rid of them. For the most part, polychaetes are harmless or even beneficial, so you shouldn't worry about them unless the animal is really large (in this context, a large polychaete is more than several inches long, or the diameter of a pencil or so), or you see them causing some damage. Ron Shimek presents some additional information on undesirable polychaetes (particularly the section "Unintentionally Added Worms - Marine Aquaria") in the aquarium in his October article entitled Segmented and Vermiform .

One thing that Mike fails to mention is his FAQ refers to the sudden appearance of swimming polychaetes in your reef tank at night (question 2 above). I have answered a number of posts from people asking why their polychaetes suddenly emerge from hiding and begin swimming around the tank after the lights go out. These worms are often seen to be eaten by something in the tank, or break apart spontaneously in turbulent water flow. The answer is that these worms are likely the sexually reproductive stage of a population of worms you never even knew were in your tank. Among many benthic polychaete species, reproduction takes place in a mass spawning at the water surface.

In some species (particularly of the family Nereidae ), the entire worm transforms into a large reproductive bag called an epitoke . During this transformation, most body segments develop large, broad-bladed parapodia and paddle-like setae for increased swimming efficiency, the eyes become enlarged and the antennae and other appendages of the head often become reduced. In other species (the family Syllidae , for example), an epitoke is formed by asexual reproduction (either through fission or budding from the posterior end). In still other species, the hind portion of the worm becomes engorged with gametes and breaks away from the rest of the worm. Although it will look pretty similar to anyone but a specialist, this last case is not a true epitoke, because the reproductive portion is not a complete worm.

Nereis brandti -- a large phyllodocid polychaete from the Pacific Northwest USA. Although this animal is not an epitoke, a palolo worm eptioke would look sort of similar

An example that many people are likely to have heard of, is that of the palolo worm Palolo viridis from Samoa.

This polychaete (family Eunicidae ) undergoes mass spawnings in which the posterior 2/3 of the body becomes filled with gametes, breaks away from the anterior portion of the body, and swims to the surface. There are so many swimming worms that the natives (and most reef inhabitants) collect them for food (it is also supposed to be a diving attraction -- paled only by the mass coral spawnings of the GBR-- to "bathe" in the gametes of the spawning worms). Once at the surface, the ripe gametes are released, often in an explosive eruption of the swimming worm, and fertilization takes place.

To get back on topic, you've just discovered a polychaete in your tank and you're concerned -- what is my advice? If they are not causing any damage, and are not very large or in high densities, you probably should not worry. So, what if the worms are very large, or extremely abundant, or are causing damage in your tank? Well, then you obviously want to remove them, but the question is how? There are a number of options that have been suggested on the newsgroups that seem pretty extreme to me (such as isolating the rocks in which you think the worm(s) is(are) hiding, and adding CO 2 to water to force them out, etc.). Just to reiterate this point from above, you should NOT bleach the rocks or such to rid yourself of a polychaete scourge. In my opinion, the best options remain the simplest ones used for as long as people have been keeping reef tanks.

1) If the worms are aggregating on some specimen, then simply remove that piece and clean all the worms off with a soft-bristle toothbrush or some such thing. If they come back, clean them off again, until you get them all. Some species (such as Oenone fulgida ) are problematic but are not so easy to deal with, because they rarely emerge completely from the rock in which they live, instead keeping their posterior end anchored in their burrow/hole while stretching their body out to forage. These worms are quite thin, and can become very long (Ron Shimek, reports having seen individuals as long as 15"!). Despite their small diameter, they can kill relatively large prey by suffocating them with a viscous mucus (Shimek, 1996), and can apparently kill animals as large as Tridacna clams by boring into the clam and feeding on the body (Delbeek and Sprung 1994). Because these worms are nocturnal (only active at night), it is difficult to remove them manually from their prey as I just suggested, so try the next solution.

2) If it is a single very large worm that you're after, you can try to remove it by hand. If you think that you can actually grab it with your fingers, but are worried that the animal is a fireworm, use a NEW pair of rubber gloves, or better yet, a pair of tweezers to catch the animal. In most cases a good pair of tweezers will succeed where clumsy fingers fail... If you find that the worm is too fast, or too skittish for you to get close to it, try using a penlight with a piece of transparent red plastic (like the sort sold for use on overhead transparencies in stationary stores) taped over the end at night. This strategy is really the only option for nocturnal worms like Oenone described above, because you'll be able to see the worm using the filtered light, but they don't generally react to it. You don't have to catch the whole worm to get rid of it. If you can grab hold of and remove just the head, you'll be fine. It is true that some polychaetes reproduce asexually by splitting, but these cases are few, and the worm must first develop a new head somewhere down the body for the posterior section to survive. If you grab only the front half of the worm, it is unlikely to be ready to split, even if it is a species which can reproduce in this way, and the back half will almost invariably die. If you miss the head, there is a reasonable chance that the worm can regenerate the remainder of the body, though, (depending on how much you remove) so make sure you get the right end.

3) If there are too many to try grabbing them one-by-one, or you just can't catch the little sucker, try a commercial or homemade bristle worm trap. There are a number of them likely to be available at your local fish shop, or by mail order, but they are easy to build, too. All you need is a CLEAN plastic soda bottle. Cut the top off the bottle at the point where the neck becomes the same diameter as the bottle

Then turn it around and hot-melt glue the top back into the bottle in reverse (you can do the same thing with a funnel, but it's more expensive and harder to get "just right."). You'll now have a slanted neck into a small hole which is easy to get into, but difficult for the animals to escape from (especially if you use clear plastic). Simply fill the bottle with tank water, add a piece of tasty bait (such as squid, shrimp, or clam) into the bottle, and leave it on the bottom of the tank overnight. This handy trap works well for mantis shrimp also. If you don't plan on using the trap for an extended period of time, or the critters you're trying to trap are small, you probably don't even need the hot-melt glue (the tight fit keeps the top in place), but I've had one fall apart on me while I was lifting it from the tank, and have used a couple of small blobs of hot-melt glue "just to be sure" ever since.

Homemade bristleworm trap

4) Purchase a predator (such as an arrow crab, or a wrasse) that is likely to eradicate the worms for you. In theory this option sounds great, but it has one major drawback. Most predators do not differentiate between the worms you want to keep and those you want eradicated. Arrow crabs ( Stenorhynchus seticornis ) are especially bad for eating desirable species of polychaetes (including "featherduster," "peacock" and "christmas tree" worms).

On the other hand, arrow crabs do have the distinct advantage that they are one of the relatively few species that are willing to happily munch on the fireworms (such as Hermodice carunculata , pictured above).

Christmas tree worm Spriobranchus giganteus

If your problem worm infestation reaches the point that you are concerned about losing some prized specimen, you may well be willing to sacrifice or move some of your benign polychaetes for the cause.

5) Clean your tank, and pay better attention to husbandry techniques in the future. Polychaetes are by-and-large opportunistic scavengers, carrion-feeders and predators. If they are flourishing in your tank, there is likely something wrong. Either they are preying on something (in which case you should worry that it may be a prized specimen), or they are scavenging or eating carrion (in which case you should be worried that your tank is loaded with organics). I have yet to see an outbreak of scavenging or carrion-feeding polychaetes (most commonly a species of Eurythoe or Eunice ,

Small fireworm Eurythoe complanata

such a Eurythoe complanata or Eunice antennata , pictured here) in a tank which is well maintained and not overfed.

There are occasions when predatory polychaetes can become numerous enough to be problematic in even the most pristine reef tank, but it is generally obvious what these animals are trying to eat, and they can probably be trapped or physically removed (see #1 & 3 above). The same is not generally true of scavenging worms -- they will be reasonably well-distributed throughout the tank, and baiting is only a temporary fix (and generally not a very efficient one) for a more insidious problem.

Despite the fact that I often use scientific names for the worms to which I am referring, in practice, one need only concentrate on the polychaete families to be able to identify and know something about the habits of most polychaetes. I have spent some time in the last article and the beginning of this one describing the general biology and morphology of the annelids, but am starting to concentrate primarily on polychaetes, and will spend the next article or two specifically describing some of the common families of polychaetes and explaining a bit about each group.

Scavenging polychaete Eunice antennata

Polychaetes are an important, but much maligned, part of a healthy reef environment. I think that people's natural dislike of "wormy" things, combined with a couple of dangerous members of the class has lead to a great overestimation of the dangers of having "bristleworms" in the reef tank (despite the fact that many members of the class are quite beautiful and are highly desirable additions to a reef aquarium). Next month I plan to describe at least a few of the more than 80 families of polychaete worms in greater detail, and hopefully dispel some of the needless concern about discovering a polychaete in your home aquarium.

Literature Cited:

Brusca, R.C., & G.J. Brusca, 1990.


Sinauer Associates, Inc. Sunderland, Mass. 922 pp.

Delbeek, J. C. and J. Sprung. 1994.

The Reef Aquarium

. Ricordea Publishing. Coconut Grove, FL. 544 pp.

Ruppert, E.E. & R.D. Barnes, 1994.

Invertebrate Zoology, 6 th Edition

. Saunders College Publishing, Harcourt Brace College Publishers, Orlando, FL. 1056 pp.

Moe, M.A., Jr., 1993.

The Marine Aquarium Reference: Systems and Invertebrates

. Green Turtle Publications, Plantation Florida, 512 pp.

Noreen, M. Bristleworm Factsheet and Mini-FAQ v0.92

Morris, R.H., D.P. Abbott & E.C. Haderlie, 1980.

Intertidal Invertebrates of California

. Stanford University Press, Stanford, CA. 690 pp.

Shimek, R. 1996. Segmented and Vermiform, it's a way of life.. Aquarium.Net Cybermagazine. October Issue, 1996.

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Last modified 2007-10-02 02:59