Everything You Wanted To Know About Bristleworms...


Big and BAD!
Jan 20, 2006
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I found this while trawling the net and thought some onbe may find it usefull


This document is part of the Reefkeepers initiative to get an updated set of FAQs out on the net. The idea being that you can be directed here to find some answers to common questions rather than having answers to the same questions posted repeatedly on the mailing lists. If you have a worm in your tank, and are not sure what it is, or what to do, please take the time to read through this little guide before you post a question listed at the end of this guide to the newsgroup (and since Ron Shimek and I have both been writing about these things for the past couple of years, I'm going to refer you to many of our more detailed and accurate articles throughout this FAQ - they will likely help far more than this guide).

Anyhow, the reason that you're probably here is that you've just recently set up a reef tank. You've added all the live rock, and possibly some live sand, you've bought a variety of invertebrates and possibly several fish to stock in your tank, and you've sat back to admire you accomplishment and relax in front of your aquarium. You drop in some food, grab a drink and sit down to admire your beautiful tank, only to notice this ugly centipede-like worm crawling out of the sand, gravel, or from under a rock to head for that brine shrimp that just settled onto the bottom of the tank.

You find yourself in a panic about what to do. What is that thing? Is it dangerous? Will it kill your corals or your giant clam? What does it eat? Should you kill it? How would you do that?

Well this is probably only your first in a long line of surprises when getting into this hobby, so relax, read through this little guide and find out what that worm is, and why it's probably a good thing to have a lot of them in your tank.


I give a much more detailed list of my background and expertise in the Home Breeders FAQ, and so will just summarize my history here. I am a Canadian, born and raised in Edmonton, Alberta. If I had to pigeon-hole myself into a specific field, I would say that I am an Invertebrate Larval Biologist, but my interests are fairly diverse, and my current research is more along the lines of marine invertebrate population genetics and evolutionary biology than larval biology.

I did my Masters degree in Marine Biology at the University of North Carolina, where I worked on the reproductive biology and larval settlement of tube-dwelling polychaete worms (Hydroides dianthus). At the time of writing this, I am a Ph.D. candidate in the Population Biology program at the University of California in Davis working under the supervision of Rick Grosberg, Gary Vermeij, Dennis Hedgecock, Brad Shaffer, Maureen Stanton and John Gillespie. Although I'm a marine biologist, I'd have to say that aquaria are my hobby rather than my work. My dad owned a pet shop when I was a child, and got me into fish keeping as soon as I was old enough to say "fish." I've had freshwater tanks as long as I can remember, and my dad got me into breeding guppies on my own about the age of 5. I've been keeping fish and trying to breed everything I can get my hands on ever since. Aside from maintaining over 30 tanks in my home, I had a variety of aquarium-related jobs before starting my dissertation (from dolphin-trainer to managing the fish department of a local pet shop, to a variety of independent aquarium consultant positions). At the time I wrote this, I have been keeping tanks for over 25 years, have had a little over 12 years of experience with marine/reef aquaria, and about 8 years of experience breeding and raising marine invertebrates for both my research and at home.

I have been writing aquarium articles for Aquarium.Net over the past couple of years now, and have a more-or-less complete listing of my aquarium and profession publications on my CV (http://biogeek.ucdavis.edu/rob_cv.html) if you're interested.

Other than that, if you want to contact me about any comments, questions, suggestions,complaints, death threats, etc., etc., please send me Email at:

[email protected] or [email protected].


This text is copyright © Robert Toonen, but may be freely reproduced for non-profit purposes as long as it is not altered in any way and the authors name is not removed (that's what every FAQ seems to say, isn't it?). Any commercial use of this text (i.e., in publications) is only permitted with the express written consent of the author. I must make a disclaimer that this text is as accurate as I could make it, to the best of my knowledge, for the size of this document. Despite the many omissions and possible inaccuracies herein, I covered what I deemed important for the FAQ, and provided some pointers to additional sources where I deemed it appropriate. I did the best I could (or at least was willing to do) at the time, so if you notice blatant errors, please contact me (Email at "[email protected]" - preferably with the text that you think should be included to "fix" that error) and I will update the document. To quote Mike Noreen's bristleworm FAQ, "I am not responsible for any actions or losses or altered mental states resulting from the reading of this text or following advice given in it." I'll do my best to give you my honest opinion on this stuff and tell you some information about bristleworms in the aquarium, but from there, you're on your own...

1. So what the heck is a "bristleworm" anyway?

"Bristleworm" is a term of which I am not particularly fond, because it means a wide variety of different things to different people. In Part 8 of my guide to Invertebrate Zoology for Reefkeepers (http://www.aquarium.net/0697/0697_2.shtml) I explain why I prefer to avoid the term in favor of the proper name "polychaete":

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 [http://www.rtop.com/features/bristleworm.shtml/], 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.

OK, I should back up a step here, and ask you to think back, waaayyy back to grade-school biology class where you learned about the classification of life. All living things on the planet are classified in a hierarchical scheme starting with Kingdom, moving down through less and less inclusive taxonomic units (namely Phylum, Class, Order, Family, Genus, species). Remember that stuff? Well, in order to talk about polychaetes, I first need to explain that the Phylum Annelida (the ringworms) contains three classes: the earthworms and their allies (Oligochaeta), the leeches (Hirudinida) and the <sigh> "bristleworms" (Polychaeta). I explain what characters define these classes and provide some information about the basic biology of the first two groups in Part 7 of my invertebrate zoology series in the Aquarium.Net archives(http://www.aquarium.net/0597/0597_5.shtml).

The polychaetes comprise the majority of species for this group, with somewhere between 8,000 and 10,000 species currently described (depending on who you ask), and there are likely at least as many more currently undescribed. There are some 80 to 90 Families (again depending on who you ask), and this is the taxonomic level likely to be of most interest to aquarists. The reasons for that are: 1) you have a reasonable chance of identifying a worm in your tank to the level of family, but, if you need to read this guide, you have virtually no chance of identifying a worm to species level; 2) there are really only about 20 or so families that are likely to be seen in the aquarium; and 3) the characteristics of a family are enough to make some reasonable generalizations about the behavior of its members.

Perhaps more importantly than the Families, in terms of the aquarists' point-of-view, worms can be grouped into two primary functional categories: "errant" (free-living) and"sedentary" (staying in one place, and typically living in a tube). I provide a family-by-family look at the polychaetes likely to be imported into reef aquaria in a series of 4 articles for Aquarium.Net (parts 9 through 12 of the invertebrate zoology series). Ron discusses intentionally and unintentionally added worms (http://www.aquarium.net/1096/1096_3.shtml),general worm biology (http://www.aquarium.net/1197/1197_4.shtml) and even some mutualistic relationships among certain worms and seastars (http://www.aquarium.net/0198/0198_3.shtml) inhis articles in the Aquarium.Net archives. These articles are great places to learn more about the biology of some of these animals, and to find some pictures and descriptions of the animals so you can figure out what is in your tank.

So what exactly do polychaetes "do?" Well, together with a multitude of small arthropods, polychaete worms fill more-or-less the same ecological role as insects on land. Sure there are some insects (like wasps, for example) that you'd prefer to avoid, but for the most part we ignore "bugs" around us, and many of them are actually beneficial, or at least provide food for many animals higher up in the food chain (see Ron's talk on sandbed function for a description of how food chains work -http://www.reefs.org/library/talklog/r_shimek_090698.html). Polychaete worms are extremely abundant in all marine habitats, and there is not a reef tank in existence that could AVOID having polychaetes in it (unless the tank was stocked completely with Aragocrete or some such artificial substrate, but even then animal additions would almost certainly bring some polychaetes along at some point). Most reef habitats that have been studied find on the order of 10-20,000worms per square meter, and in some muddy bottom areas with high organic input, densities ofworms can reach over *half a million* per square meter!

Thus, it is safe to say that you, and everyone else with a reef tank already has "bristleworms" in it. It is impossible, however, to make a general statement about what worms do and how they function, though, because nearly every marine phylum includes something that the average aquarist would call a "worm" (and I'll cover a few of these at the end). Even among the polychaetes it is impossible to make a general statement about the tendencies or appearance of worms above the level of Families because they are such a diverse group (I discuss this in much more detail in Parts 7 & 8 of the reefkeeper's series --http://www.aquarium.net/0597/0597_5.shtml & http://www.aquarium.net/0697/0697_2.shtml). It is possible, however, to make some general statements about the families which fall into the two functional groups (sedentary and errant polychaetes) I mentioned above, and I will now try to cover each group in a little more detail, before ending with a "question & answer" type format for some of the most commonly posted questions I have seen over the past couple of years on the net.

2. Sedentary polychaetes.

The sedentary polychaetes are the focus of parts 9 (http://www.aquarium.net/0897/0897_5.shtml) and 10 (http://www.aquarium.net/1197/1197_1.shtml) of the reefkeeper's guide to invertebrate zoology series. In these two articles you will find a series of pictures and a basic description of each class that I believe is likely to show up in a reef tank. Because this information is readily available elsewhere, I will not try to cover the families of sedentary polychaetes again, but rather will try to give an overview of the groups.

In general sedentary polychaetes stay in the same place. Most of them build tubes which are temporarily or permanently attached to the substrate, and the majority of them feed by filtering plankton and other tiny particles from the passing water or collecting organic detritusfrom around their tubes. As such, these worms are harmless, and often attractive additions to a reef aquarium. These are the worms most likely to be purchased and added to a reef tank intentionally, because many have brightly colored tentacular crowns that make them an attractive addition to any tank. These tentacular crowns generate a feeding current by which the worms selectively collect tiny food particles from the water column (see Ron's Segmented and Vermiform article -- http://www.aquarium.net/1096/1096_3.shtml -- for a description of how this feeding works). The crowns are retractable, and in some families protected by a little "cap" (the operculum) which seals the tube when the worm retracts inside. These groups include such well-known species as the Christmas Tree Worm (Spirobranchus giganteus), the Peacock Worm (Sabellastarte magnifica) and the Featherduster clusters (Sabella melanostigma) sold at the local pet shop (see the above articles for pictures and more details regarding these worms).

The problem with adding these attractive species is that most tanks lack the supply of phyto- and/or zooplankton on which these worms feed. They are *not* photosynthetic, and cannot use light to supplement their feeding as can corals. If you have a relatively new tank, and you are not regularly feeding the tank (see Ron's article on feeding corals -http://www.aquarium.net/0197/0197_4.shtml - for why this is important, and why you should start if you're not) with greenwater and/or rotifers (I have an article at http://www.garf.org/news13p2.html#green on how to culture greenwater at home, and another at http://www.aquarium.net/0397/0397_5.shtml on how to culture rotifers), I would recommend against adding any of these filter-feeding worms, because you will likely sentence them to a long, slow starvation (most invertebrates are capable of digesting their internal organs to slow the effects of starvation, and can last months or even years without food as they slowly digest themselves from the inside and shrink to a fraction of their original size before dying).

Another type of sedentary polychaete worm has a number of stringy spaghetti-like tentacles rather than a fan-like tentacular crown. These are the well-named spaghetti or sand-mason worms (again see http://www.aquarium.net/1197/1197_1.shtml for pictures and a descriptionof these animals). These worms generally feed by sending out their spaghetti-like tentacles (some of which can stretch up to 1 m in length!) from their burrow in search of tasty morsels (primarily organic detritus and any dead matter). If the particles are small, they can be simply run down the U-shaped tentacle to the mouth without any interruption in it's search for food. If the food particle located is too big to fit into the food groove, the tentacle can be wrapped around the item and pulled back to the mouth. In those rare cases when a large food item is located, multiple tentacles may be recruited to help drag the food item to the mouth. These worms are great additions to most aquaria, especially those based on a "live sandbed" because they help with the cleanup of excess organic detritus in the tank.

3. Errant polychaetes.

The errant polychaetes move about in an active search for food, although some may setup a "home base" parchment tube under a rock or in a crevice. These worms generally have a large and obvious head region, and lack the fan or tentacular crown that makes the sedentary polychaetes so attractive. Instead these worms resemble centipedes (at least so I gather from the typical posts to the newsgroups asking "what is that centipede-like thing in my tank?"), and typically have a strong set of jaws that are capable of being thrust out during feeding. They are not in any way related to centipedes, and the "legs" are really parapodia (see Parts 7 & 8 of my articles, or Ron's "As the worms turn" - http://www.aquarium.net/1197/1197_4.shtml - for a description of basic polychaete anatomy).

It is the errant polychaetes that are usually the ones that elicit the response that I outlined at the beginning of this FAQ, and includes those few species that can be trouble-makers in a reef aquarium. These worms are the focus of Parts 11 & 12 in the reefkeeper's guide to invertebrate zoology series (http://www.aquarium.net/0198/0198_2.shtml & soon-to-be-released). Again I would suggest that you go to check these articles for more details on the individual groups and some pictures of what each looks like.

Many of these Families have members that are active scavengers and predators, but most are opportunistic, and even the predatory ones tend to consume other worms, microcrustaceans, bacteria, detritus, algae, and other material which serves a positive function in the aquarium. In general these worms crawl about on the bottom, burrowing through sand, peeking out of rocks, algae, or whatever else there is to crawl in in your aquarium, but some are also capable of swimming (some more gracefully than others). Swimming worms may be simply an individual that was displaced and swept away by the current, or it may be the reproductive stage (an epitoke) of one of the bottom-dwelling species (I'll discuss epitokes further in the Q&A section at the bottom). Probably >99% of errant polychaete worms fall into the category of innocuous scavengers, but there are a few notable exceptions that may prey on corals, clams and snails, and even small fishes. It is these exceptions of which the aquarist need beware, and for which the entire group has gotten it's Bugbear reputation.

These few potentially dangerous species, primarily in the Family Amphinomidae (see http://www.aquarium.net/0198/0198_2.shtml for a detailed description), are the ones that have given the entire group of polychaetes a bad name, because they are the obvious and problematic ones. They are generally regarded as repulsive creatures which move in a manner reminiscent of a creature from a 1950's B-rate horror picture, and some can pack a nasty sting or bite. It is these few species (and particularly Hermodice carunculata) that cause panic among reefkeepers throughout the world, and yet, in my entire time keeping reef tanks, I have only seen ONE aquarium in which Hermodice had become established and problematic.

Some of these worms are potentially quite toxic, however, and as such, if you discover a polychaete in your tank that looks like a "wooly-bear" caterpillar (again check out http://www.aquarium.net/0198/0198_2.shtml for pictures and more information), 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 latex rubber dishwashing gloves (PLEASE get a new pair for this purpose and rinse them well before you put them in your tank -- and *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. 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. 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 (and, as I just said, I have only seen 1 tank with H. carunculata in it). 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). 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). If available, meat tenderizer is supposed to work exceptionally well, although I have never tried this myself (fortunately I have had very few encounters with stinging marine organisms despite my occupation <g>).

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 for your corals and fishes. A safe rule of thumb is to ignore a polychaete worm unless it gets very large (pencil diameter - length is not really important) or proves itself to be a trouble maker (attacks something such as a clam or coral in your tank). See Part 8 of my reefkeeper's guide for more information on how to remove problematic worms from the tank(http://www.aquarium.net/0697/0697_2.shtml).

4. Oddities and other "wormy" things that are NOT polychaetes.

A "worm" is pretty much a long cylindrical animal. In general any soft-bodied, tubular animal whose length far exceeds its diameter would be dubbed a "worm" by most observers. Given that definition, there are "worms" in virtually every phylum of animals, and this often leads to confusion.

Worms are confusing because most people are used to being able to identify animals by their shape; looking at a fish or a coral, it is obvious (despite the multitude of shapes and sizes) that they are all related in a single group, and small differences don't really affect our ability to recognize that group. When it comes to wormy things, however, people generally notice the shape and miss the small differences that are essential to recognizing groups. Ron Shimek has an excellent article on wormy things (vermiform animals) athttp://www.aquarium.net/1197/1197_4.shtml which explains how worms work, lists the common aquarium forms, and tells why the vermiform body plan is such a common and successful one. I won't try to cover any of the animals in great detail here, but rather list some of the most common "worms that ain't" (to quote Ron) and provide pointers to where you may find out more information about them. If you find this section is *way* over your head, you might want to seriously consider doing some more reading to get up to speed on some common reef critters before going much further in the hobby...

1) Ctenophores & Cnidarians:

Some ctenophores (comb jellies) , such a Coeloplana are modified into wormy crawling forms. There are also a variety of sand-dwelling cnidarians (specialized hydrozoans in particular) that could potentially be mistaken for worms.

I don't have any pictures of these benthic (bottom-dwelling) forms in my article, but I describe what they are and something about the biology of both of these groups in my gelatinous zooplankton article (http://www.aquarium.net/1296/1296_8.shtml).
2) Platyhelminths and Nemerteans (the flat and ribbon worms):

Both flatworms and ribbon worms are occasionally mistaken for polychaetes, although polyclad flatworms are more often mistaken for nudibranch molluscs. Of course, they are neither, and the lack of "bristly legs" on the animal should immediately eliminate that possibility for you./P>

My article on these animals (with pictures provided by Ron) can be found athttp://www.aquarium.net/0297/0297_5.shtml. Ron also covers these groups in his article on vermiform animals (http://www.aquarium.net/1197/1197_4.shtml).
3) Rotifers and other tiny critters:

With the popularity of these animals as a food source, rotifers are becoming a household word. The common planktonic rotifer used for feeding marine larvae (typically Branchionus plicatilis) is actually among the minority for this group, however, but the tiny benthic wormy forms are unlikely to be seen without a microscope (I discuss the biology of rotifers and their culture in http://www.aquarium.net/0397/0397_5.shtml and Ron mentions them in his vermiform article, listed above).

Also included in this group are a variety of tiny (and primarily sand-dwelling) critters that you are unlikely to have heard of before, including gastrotrichs, kinorhynchs, nematodes, priapulids, petastomulids, acanthocephalans, gnathostomulids, loriciferans, and tardigrades. These obscure groups are generally of interest only to invertebrate zoologists, but if you want to find out more about them pick up one of the general invertebrate zoology texts listed in the"Other Resources" section at the end at your local library.

More commonly, people mistake the larval form of some groups (particularly sponges and cnidarians) for tiny worms when seen. In general these larvae are small (1-2 mm) nondescript blobs that glide about the tank looking for an appropriate place to settle and metamorphose into the adult body form.
4) Sipunculids (the peanut worms):

The peanut worms are a funky group of blunt worms that tend to make their presence known by pushing a small cap of tentacles out of holes in live rock (they almost always arrive in holes or burrows in live rock). The most distinctive habit of sipunculans is that the structure which emerges form the live rock (known as the introvert) unrolls itself from the inside out. This is most easily compared to the finger of a rubber glove that has been inverted when you pulled your hand out of it, and then extended by blowing into the glove. Both Ron and I have articles in which we describe this group in more detail and discuss some of their biology (Ron at http://www.aquariumfrontiers.com/1997/dec/wb/default.asp and me at http://www.aquarium.net/0497/0497_4.shtml).
5) Vermetid gastropods (tube-snails):

Tube-snails look for all the world like a feather duster that has lost its crown of feeding tentacles. In fact, these animals are almost always one of our "were you paying attention?" questions on invertebrate zoology lab exams, because with only a casual glance at the animal, the tube looks very similar to that of a serpulid polychaete worm. Ron has a great article all about Vermetid gastropods and how they "work" at http://www.aquarium.net/0897/0897_8.shtml complete with pictures.
6) Wormy Molluscs:

There are a variety of molluscs (particularly in the classes Caudofaveata and Aplacophora, although there are others) that could be mistaken for worms. For the most part, these animals tend to be from deep sea regions, and as such are unlikely to be imported to aquaria, but I include them in the interest of breadth. The most likely imports in live sands would be the tusk shells (Scaphopods), which are tusk-shaped (hence the name), but open at both ends. The animals live face-down in the sand with only the "pointy end" of the shell usually appearing above the sediment surface.
7) Sea Cucumbers:

To many, sea cucumbers resemble worms. These echinoderms are covered in Ron's "As theWorms Turn article" (http://www.aquarium.net/1197/1197_4.shtml). In general, these animals are highly beneficial to marine aquaria as scavenging cleaners, but are often doomed to starvation in small or particularly clean (especially new) tanks. The animals slowly starve to death as they digest their internal organs and shrink until they can no longer sustain themselves and perish. One way to identify a sea cucumber is to watch their characteristic feeding behavior - they retract one tentacle at a time, stuff it into their mouth and wipe it clean before extending it again as they stuff another tentacle into their mouth. This rotating pattern of retracting feeding tentacles is a good indication that the animal is likely to be a cucumber.
8) Wormy Crustaceans:

Even a group known for being armored in a hard shell has some members which could bemistaken for worms. The members of this group are rather obscure, and unlikely to be seen in an aquarium, but again I include them for the sake of giving you an impression of just how many "wormy" animals there are. The Remipedes are a surprising group of worm-like crustaceans long thought extinct, until their discovery in marine caves on Grand Bahama Island in 1980. Some Isopods are also occasionally mistaken for worms. The use of jointed appendages for walking and swimming (see Ron's diagram of polychaete "appendages" in http://www.aquarium.net/1197/1197_4.shtml for comparison to those of a crustacean) together with the lack of sinusoidal swimming (also described in http://www.aquarium.net/1197/1197_4.shtml)should clue you in to the fact that these are not polychaetes.
9) Echiurans and Hemichordates (the tongue and acorn worms):

Both these groups are likely to be rare in aquaria, but I include them here just in case. Ron covers the acorn worms in http://www.aquarium.net/1197/1197_4.shtml. The tongue worms are a rock and sediment-dwelling group that are most likely to be imported as part of a live sand shipment, and which get their name from the long, often hammerhead-shaped ( a "T" or "Y") split right at the end of a long rubbery thread-like "tongue" that emerges from their burrow. This tongue is how they collect organic detritus and bacteria from the sediment surface on which they feed. Although they are exceedingly rare in aquaria (I have yet to see one in a reef tank), they would be a harmless and fascinating addition to a well-established reef tank with an active sandbed.
10) Chaetognaths and Cephalochordates (the arrow worms and lancelets):

Although unlikely to appear in a marine aquarium, I again include these groups for the sake of completeness. The Chaetognaths (arrow worms) are a group of predatory "worms" that feed on a variety of other animals including planktonic worms and crustaceans, small fishes and even each other, although most prefer to consume copepods. Most are planktonic, but there are some benthic forms as well. They are all relatively small (ranging from about 0.5 to 10-12 cm inlength, with the diameter of a spaghetti noodle), and unlikely to do much damage in an aquarium (unless you're trying to culture copepods), even if they were introduced.

The lancelets (cepahlochordates are frequently called "Amphioxus" in introductory college biology classes) are also very unlikely to be introduced into an aquarium, and even if they were added, would be unlikely to ever make their presence known. They are small fish-like critters that rarely exceed about 5 cm in length and generally spend their lives buried in the sediments, where they filter suspended particles from the water with only the clear tip of their head protruding from the sand. They can swim, however, it is an awkward whole body flexing (sorta like holding a willow stick at the middle and waving it quickly back and forth) that is very un-fish-like.

Well, that's most of the wormy things I can think of off the top of my head that the average aquarist might confuse with a polychaete worm. I'm sure there are many that I have missed, but hopefully this gives you a general idea that a "worm" could be an awful lot of different things, and you need to know something about the identity and habits of a mystery critter before posting a message to the group asking "I have a worm. Is it dangerous?"

5. Frequently posted questions about polychaetes.

So here I will try to answer some of the most common questions that I have seen posted to the reef groups to which I subscribe over the past couple of years. I'm sure that I will have missed many important and common questions in this section, so I expect that it will be updated periodically.

Q: I've just noticed this ugly centipede-like worm crawling out of my sand/gravel/from under a rock -- is it dangerous?!

A: Most likely not. As I mentioned above (several times) the vast majority of polychaetes are harmless, and many are beneficial to your tank. Unless the worm is more than ~6 inches in length OR approaching the diameter of a pencil, you shouldn't worry too much about having "bristleworms" in your tank. Remember that it is impossible to AVOID introducing some polychaete worms into a tank with live rock, and they're nearly always harmless. If the presence of the worms worries you, by all means keep an eye on them to see if they cause any real problems, but it is best to leave them alone until you see some evidence that they are causing trouble

Q: My feather-duster/peacock/christmas-tree worm has crawled out of it's tube. Why?

A: This is a serious stress response -- most likely it is dying. Although some worms can recover if gently placed back into their tubes, it is generally safest to remove it before it rots. This is likely to be a sign of poor water quality, and you should pay extra attention to your tank parameters.

Q: My feather-duster/peacock/christmas-tree worm has lost its head! Is it dying?

A: Not necessarily, although this is again generally a serious stress response. A new tentaclular crown can grow back if the water conditions are ideal, but you should again pay special attention to your tank parameters when this happens.

Q: How much light does my feather-duster/peacock/christmas-tree worm require?

A: Because it's a "filter feeder" it does not need any light - it's not photosynthetic. Instead it needs a constant supply of suspended organic matter which it can filter from the water. This means you should *not* consider getting one of these animals unless you intend to feed it. See Ron's Segmented and Vermiform article -- http://www.aquarium.net/1096/1096_3.shtml -- for a description of how filter feeding in worms works.

Q: Where should I place my feather-duster/peacock/christmas-tree worm in my tank?

A: These animals generate feeding currents, but they also use existing currents to aid them. Thus, they like moderate and consistent currents. They can get by without any current, but mostdo poorly with too strong a current.

Q: OK, I know most worms are harmless, but I've got some of the 'bad boys' in my tank - how doI kill them?

A: There are a variety of ways to deal with trouble-making polychaetes. I outline them in my article at http://www.aquarium.net/0697/0697_2.shtml, but the quick answer is:

* Get or build a trap (e.g., a soda bottle or nylon stocking can sometimes work). This only works moderately well for some species.
* Manually remove the worms with a siphon tube or pair of tweezers -- make sure to get the head, since a decapitated worm can sometimes regenerate it's body.
* Add a predator (such as an arrow crab or a wrasse). The problem with this is that predators don't differentiate between the worms you want, and the ones you don't....
* Clean your tank and pay more attention to husbandry techniques. Although there are some worms that are just trouble, many don't become a problem unless there are other issues that allow it.

Q: Why not just kill the worms by treating the live rock with (insert your favorite over-reaction here -- treating with copper sulphate, fresh water dip, carbonated water dip, high/low pH or salinity dip, bleach, boiling etc...)?

A: Because it's just plain stupid. All of those recommendations are pretty much guaranteed to kill the life that you paid so much to get on your rock, and are generally likely to seriously affect the beneficial bacteria in the live rock (the "filtration function" for which one uses live rock in the first place). If you feel the need to resort to such drastic treatment, you may as well throw your rock away and start again from scratch.

Q: I've found some hard, white organisms growing on the glass/rocks/sump in my tank -- what are they?

A: Well, this isn't easy to answer, because it could be a variety of things. In general, there are a few likely candidates that are common to new tanks, though. First, if it's a tightly coiled spiral that is no more than a few mm in diameter, it's most likely to be the tube of a Spirorbidpolychaete. If it's more straight or wavy than tightly coiled, it could be a Serpulid (I cover both of these with pictures in http://www.aquarium.net/1197/1197_1.shtml). Both are harmless filter feeders, which tend to go through periodic population explosions, especially in new tanks (they usually come under control or even completely disappear as the tank ages). Another other common possibility is that the critter looks more rice-grain-like, possibly with a tuft of "hairs" sticking out like a tiny funnel at one end. This is most likely a calcareous sponge rather than a worm, and you can find out more about sponges athttp://www.aquarium.net/1196/1196_7.shtml. The final possibility is that the critter is loosely coiled, or more blob-like with fine hairs sticking out of the body all over the surface. This is most likely a foraminiferan - check out http://www.ucmp.berkeley.edu/foram/foramlh.html for a(lousy, but live) picture and some basic information about their biology, orhttp://meguma.earthsciences.dal.ca/~reinhard/foram.html for a decent (but dead) picture and some more basic biology information.

Q: I see some long, weird translucent tentacles coming out of my live rock! What is it?

A: These are most likely the tentacles of a Terebellid polychaete (better known as Spaghetti,Medusa or Mason worms), although a recent thread that started like this turned out to be a sipunculid (see Section 4, #4 above). Some of these animals can get quite large (some species have tentacles over 3 feet long!). I discuss these worms in more detail inhttp://www.aquarium.net/1197/1197_1.shtml

Q: There are parasitic worms all over my soft corals! What do I do!?

A: If you see worms (of whatever sort) consistently aggregating on a coral or clam, etc., they are most likely feeding on it. Although there are a variety of acoel flatworms that survive off outputs by their algal symbionts (apparently aided by some grazing on the mucus released by their host),unless you know what the worm is and what it's doing on your coral/anemone/urchin/nudibranch/whatever, it is safest to simply siphon them off every time you see them. This is usually the least stressful and often easiest way to remove the worms from your tank (both for you and your critters). If siphoning fails to dislodge the animals, you can take the coral/clam/whatever out of the tank, and gently rub the worms off with a soft toothbrush in a bucket of saltwater. This procedure will likely need to be repeated several times before the population is eradicated.

Q: Everything has been fine with my tank for the past year or two, but I've just discovered I have a large population of bristleworms. Should I be worried?

A: Probably not. The worms are likely to have been there all along, and if they haven't caused any damage by now, chances are they never will. However, you should be aware of what has changed that caused you to notice the worms now. If the population has increased dramatically it may be a symptom of a larger problem that requires attention. If you noticed just because it was the first time that you snuck up on your tank with a flashlight at night, then you probably don't have to worry....

Q: How do polychaetes reproduce?

A: Most polychaetes reproduce sexually, and the majority of them produce planktonic larvae. However, there are some species that reproduce either ameiotically (produce unfertilized eggs that develop into juveniles) or through fission (some part of the body develops a new head and the worm breaks in half). Polychaetes are relatively easy to raise in captivity (at least compared to most of the other critters we keep in our tanks). I have pictures of a polychaete larva inhttp://www.aquarium.net/0897/0897_5.shtml and some pointers to my Home Breeders Guide to raising marine larvae. Ron has some great pictures of polychaete larvae captured from his reef tank in his article: It's (in) the Water (http://www.aquarium.net/0997/0997_4.shtml). If you're interested in breeding some of the critters in your tank, polychaetes would be a good "guppy" for you to experiment upon - check out my Home Breeders Guide for more information on how to breed and culture your critters.

Q: Last night I peeked into my tank and was surprised to see a bunch of swimming worms --what are they?

A: Most likely these are the reproductive stage, called an epitoke (which I mentioned briefly above), of certain bottom-dwelling polychaetes. They are usually observed to be eaten by a fish,or simply spontaneously explode in a high current area or upon reaching the surface. This is thought to be an adaptation for concentrating gametes and enhancing fertilization among a cryptic and highly dispersed population of burrowing worms that are unlikely to find a mate otherwise. If you have multiple epitokes in your system at the same time, you could try to collect them and use the gametes contained within to start a culture of worms to raise. I discuss epitokes in more detail at http://www.aquarium.net/0697/0697_2.shtml

Well, I hope I have answered some of your questions, and that, if nothing else, this FAQ has encouraged you to read a bunch of more detailed articles and learn a lot more about your critters and your new hobby! Good luck, and happy reefing.


Moe, Martin. 1992. The Marine Aquarium Reference: Systems and Invertebrates. Green Turtle Publications, Plantation Florida. 512 pp.

Morris, R.H., D.P. Abbott & E.C. Haderlie, 1980. Intertidal Invertebrates of California. Stanford University Press, Stanford, CA. 690 pp.

Shimek, Ron. Various hyperlink pointers included within the FAQ - available from theAquarium.Net and Aquarium Frontiers archives.

Toonen, Rob. Various hyperlink pointers included within the FAQ - available from theAquarium.Net archive.

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