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Polychaetes by Rob Toonen August 1997 Aquarium.Net

This month Rob Toonen covers Polychaetes, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Reefkeepers Guide to Invertebrate Zoology

Part 9: Polychaetes

By Rob Toonen

I apologize for missing last month's deadline for an article -- my computer with the slide scanner was tied up for 15 days in a massive simulation, during which I was afraid to scan anything for fear of hanging it, and after which my hard drive crashed at the most inopportune time. Fortunately, I had everything backed up, but it took me a few days to buy a new hard drive, reinstall everything and get my computer running again, and unfortunately, by that time it was too late to submit this article.

Anyhow, excuses aside, I'll continue where we left off in the last article. As I said there, you really only need to know some basic information about each of the most common families of polychaetes to be able to communicate with others about the the worms you're likely to encounter in any reef tank. Polychaete taxonomy is notoriously bad, and even among polychaete specialists there is often disagreement about species identities, so don't worry too much if you're unsure whether you have species A or species B, because many invertebrate zoologists couldn't tell you the species identity with absolute confidence, either. In fact, the more closely people look at polychaete "species" the more often they find that either: 1) there are two or more very similar species included under a single species name, or 2) animals given different species names are, in fact, the same species, but just show environmental plasticity (exhibit different physical or reproductive traits in different environments). This fact alone makes identification very difficult, and the lack of people doing serious alpha-taxonomy (identifying and describing new species from intensive collections and morphological study of "type specimens") on any group, let alone polychaetes, just amplifies the problem. I don't mean to cast such a dismal picture in regard to polychaete systematics, but it is definitely an area that is under-staffed.

Despite that dismal forecast, the average aquarist need only know some basic details of the biology of the most common families to be reasonably well-equipped to deal with "bristleworms" in the reef aquarium. As I promised in the last article, I will spend the rest of this article (and the next as well) detailing some of the most common families of polychaetes, their characteristics, a bit about their biology, and hopefully a picture or two for people to be able to identify the families based on my feeble descriptions (it is difficult to accurately describe polychaete families in a way that is accurate but not overly technical). Of course a single example cannot be representative of EVERY member of any group (especially among the polychaetes, which are unusually diverse), but by comparing your worm to a "typical" representative or two for each group (as I said, I have tried to include pictures of at least a single species of each group I discuss, but other texts will have more photos and examples), most polychaetes encountered should be identifiable, at least to the family level.

As I mentioned in the last article, the traditional distinction between the Sedentaria (the non-motile tubiculous , or tube-building, worms) and the Errantia (the motile non-tube-building species) is artificial and technically incorrect. However, the functional distinction between the two, in terms of hobbyist interests, remains valid. Thus, I'll start with some of the sedentary polychaetes and finish them up next month; after that I'll start to discuss the errant families. I had originally thought to discuss each group of families in a single article, until I wrote the first and realized that it was 12 pages long, so I have split the "Sedentaria" into 2 articles, and will see whether it proves necessary to do the same with the "Errantia." The sedentary polychaete families that are most common (and that you are most likely to encounter in the hobby), are:

Chaetopteridae (kay-top-tare-id-day)

Chaetopterids are a family of polychaete worms that virtually all live in tubes or more-or-less permanent U-shaped burrows through which they pump water to filter out organic particles and respire (breathing is difficult within anoxic mud, unless oxygenated water is actively pumped through the burrow). Although there are some large, and rather spectacular members of this family along the Pacific coast of North America (e.g., Chaetopteris , pictured here, can reach the size of a felt-pen marker and build tubes that exceed a foot in length) most tropical genera (e.g., Phyllochaetopterus and Mesochaetopterus ) are relatively small and innocuous.

These worms are distinctive because they have 2-3 distinct body regions that are unmistakable. They generally have a head region which is enlarged (when compared to other polychaete worms) and from which a pair of modified parapodia (remember last article -- this is the name for the specialized "legs" of polychaete worms) extend. These parapodia are pressed against the wall of the tube or burrow, and hold a mucous 'net' or 'bag' through which all pumped water must pass (see Ron Shimek's Aquarium.Net article Segmented and Vermiform, it's a way of life for a discussion of how ciliary mucous feeding works). The water is pumped by the second part of the body, on which several large, flattened parapodia (called "fan parapodia" -- and they actually resemble Chinese paddle fans) are used to constantly push water through the tube/burrow.

Chaetopterus variopedatus , a tube-dwelling chaetopterid common in the mud flats of central California. The tube has been cut open and the animal removed for easy viewing.

Once the mucous bag/net begins to clog with organic debris from the filtered water, the modified parapodia release it, roll it into a ball and pass it along a groove to the mouth, where it is ingested. A new mucous bag/net is produced and the worm pumps water through it until it, too fills with organic particles. This entire process can take as little as 20 minutes if there is a lot of suspended organic material in the water column.

Although most chaetopterids are solitary, Phyllochaetopterus can form large aggregates on rocks, pilings, docks and other hard substrata. I have spoken to at least one person who has just such a 'fouling' aggregate in their reef tank. These worms are quite small in diameter (less than 2 mm), and have two obvious palps which extend from their tubes, leading many people to misidentify them as Spionids (discussed next month). However, their length (which can reach several inches), and the length of their palps (which can reach several centimeters), rules out the tiny spionids as a possible identification. If you were to remove one of these animals from their tube, you would also see that they have a series of several modified parapodia to hold mucous bags/nets and several sets of "fan" parapodia which would confirm that it was indeed a chaetopterid.

These worms are almost entirely harmless unless they reach such high densities that they begin to smother other animals. If you notice that a clump of Phyllochaetopteris worms is becoming very dense and is starting to crowd some prized specimen, then by all means remove some of the animals (a friend or local fish shop would likely be thrilled to take them off your hands). However, if they are not smothering anything, they are not likely to be hurting anything, and you should not worry about the discover of them in your aquarium.

Phyllochaetopterus prolifica tubes from an aggregation collected from a piling of a dock in central California. These animals are relatively small, but the long aggregated tubes and should be a give away to distinguish these worms from spionid polychaetes.

Cirratulidae (sear-rat-yul-id-day)

Although not the most common of imports, I expect that the recent popularity of live sand will lead to more of these animals being seen in reef aquaria. Cirratulids are generally shallow-water burrowers that live just below the surface of the sediment, and extend their branchiae (again these are threadlike "tentacles" used for feeding and respiration) into the water above the sand.

One exception is the reef-building cirratulid of the California coast, Dodecaceria fewkes , pictured here, which forms calcareous colonies that can be quite extensive. These worms are capable of asexual reproduction and these reefs may, in fact, be clones of successful individuals which have gone on to form their own tubes and extend the colony. Regardless of wether the animals are tubiculous or are sedentery burrowers, most are selective deposit feeders that extract organic detritus from the surface sediments.

A few (perhaps as many as a dozen) small, short tentacles emerging from the sand may be an indication of the presence of a cirratulid (many long tentacles likely indicates a terebellid , discussed next month). In some species, (e.g., Dodecaceria ), the feeding palps look remarkably like a small tongue probing the area around the tube/burrow for organic detritus to consume.

Dodecaceria fewkes , a colonial cirratulid common along the Pacific northwest coast of North America. A few of the worms have been broken out of their tubes for easy viewing .

Again, these worms are only harmful if the densities reach infestation proportions. If there are relatively few of the animals, you can safely assume that they are scavenging detritus and making your tank a cleaner and happier place for the other inhabitants.

Pectinariidae (pect-in-air--id-day)

These worms are somewhat odd, in that they form short conical tubes of sand or gravel that are open at both ends. Their bodies are short and stubby (usually only about 20 segments), with the worm's body actually resembles the short conical tubes that it builds. The tubes they build have earned them the nickname "ice-cream-cone worms."

The animals typically feed 'head down' in the sand, and create a water current that 'liquifies' the sand around the tentacled head to allow easy movement of the tentacles in their search for detritus. Again these animals are primarily selective

Pectinaria californiensis , a common "ice-cream cone" worm from mudflats throughout California. The narrow end of the tube would be at the surface of the sand, and the tentacles would be below the sediment and out of sight in a feeding worm.

deposit feeders, extracting edible organic particles from the sediment around their tube and are unlikely to be harmful except when in very high density if they start to overgrow anything else. If they are restricted to the sediment, even a very high density of the worms is unlikely to cause any hazard, but likely indicates an extremely high organic detritus load that is a symptom of more ominous problems.

Sabellariidae (sab-bell-a-r-id-day)

Like the pectinarids (above) members of this family build sand or gravel tubes in which they live, but these tubes almost never resemble an ice-cream-cone, they are typically oriented 'head up,' and the anterior setae (hairlike bristles characteristic of polychaete worms) are modified to form an operculum (a cap which seals the tube when the worm withdraws into its tube). These animals reproduce only sexually, but many species form extensive aggregations. Some species (e.g., Phragmatopoma lapidosa and Sabellaria cemtarium ) form colonies of well-developed sand tubes (earning them the common name, sand-castle worms) that can actually form extensive 'reefs' which are large and strong enough to prevent beach erosion in some places (pictured here).

Phragmatopoma lapidosa 'reef' at Ft. Pierce, Florida. This reef extends for miles and may be over 50 ft wide and 10 ft tall in some areas. There is interest in culturing these worms to form artificial reefs for aid in the prevention of beach erosion throughout the southeastern United States

Close-up a single Phragmatopoma head. Each tube is an individual worm, and the dark spot obvious at the entrance to each tube is the operculum sealing the tube until the tide returns and the colony is once again submerged to allow suspension feeding and tube repair.

These animals are particulate suspension feeders, removing organic particles and plankton from the water column for ingestion. They are unlikely to do very well in a reef tank, because they tend to live in very high energy environments (such as the surge zone), and require enough water flow to suspend sand particles which they can catch to enlarge and repair their tubes on a regular basis. I have, however, kept Phragmatopoma in standing water tanks with a powerhead directed at the colony, and just sprinkled new, loose sand across the top of the colony as previously deposited sand became incorporated into the tubes.

One interesting point to consider is how an animal that lives entirely within a tube can excrete wastes without fouling it's environment. Perhaps you have noticed a fan worm contract violently and eject wastes from its tube, or have seen a mason/spaghetti worm crawl partially out of its tube to release feces? Well, the sand-castle worms have another solution. The last segment of the worm (the pygidium , if you remember our discussion from the last article) is modified such that it forms a long tube which folds up along the body of the worm and allows them to excrete their wastes directly into the water outside the tube. Although several groups have a similar modification of the terminal segment, it is generally not so well-developed or elongated in other families as it is in the sabellariids.

These animals are only dangerous to a reef tank if they begin to overgrow some other specimens, which is unlikely given their habit of collecting suspended sand and incorporating that into their tubes -- few aquarists have enough current in their reef tank to keep the sand substrate suspended. They are filter feeders, and only remove tiny organic particles from the water column, and are thus unlikely to harm any other tank inhabitants. They are, however, prodigious spawners, and are likely to provide a significant input of "live food" to other tank inhabitants in the form of planktonic larvae. Raising the larvae is possible, albeit time and resource intensive, and if readers are interested in attempting to raise the offspring of your tank inhabitants, I suggest that you check out the general guide I wrote for The Breeder's Registry on captive culture of marine invertebrates (now available on my home page, Rick Martin's Reef Addiction page, and Jeff Pfohl's Fish Information Page).

Larva of Phragmatopoma lapidosa raised in captivity. The long setae ("hairs" along the side) are erected when the larva is disturbed, and are presumably used for defense

Sabellidae (sab-bell-id-day)

These are, at least in part, the "peacock," "fan" or "featherduster" worms with which most reef keepers are familiar (depending on the petshop in which you browse, some sabellids and serpulids -- see Serpulidae , below -- may be marked with similar common names). These worms are divided into two distinct body regions: 1) a fragile, fleshy body with special setae (again, from last article, these are the particular bristlelike hairs characteristic of polychaetes) that are used to scoot the body up and down within the tube (these are called uncini , and resemble a barbers comb embedded in the parapodia, so that all the 'teeth' stick out -- allowing the animal to grasp the smooth inside walls of the tube); and 2) an often resplendent 'crown' of feathery tentacles (alternatively called pinnules , branchioles , or radioles depending on the textbook you consult) that are extended from the tube to function in gas exchange and ciliary suspension feeding (As I mentioned above, Ron Shimek's article has a great description of ciliary suspension feeding).

Sabellids always live in tubes (at least when healthy, if you see a worm with a "feather" crown out of its tube, it is unhealthy and you should never consider buying such an animal) that are generally soft and leathery (some sabellids form calcareous tubes, but a reasonable general rule of thumb is that sabellids live in soft, leathery tubes, while serpulids -- see Serpulidae , below -- live in hard calcareous ones). The large Hawaiian fan worms, Sabellastarte magnifica (similar to Hypiscomus , pictured above) is one such example.

Hypiscomus sp., a common "featherduster" or "peacock" worm found throughout the Caribbean.

Again, as with most of the worms described in this article, these animals are generally harmless unless they reach extremely high densities. Because most of the members of this family (and the serpulids described below) reproduce sexually and produce planktonic larvae, there is little risk of them reaching high densities in a reef tank, but there are a few species (such as the "duster cluster worms," Sabella melanostigma , pictured here) that are capable of asexual reproduction, or produce such a short-lived, nonfeeding planktonic larva that they are capable of reproducing within a reef tank. Such species can become so abundant that they literally overrun other animals in the tank, but if they do so, it is likely a symptom of a nutrient problem in the tank.

Well, that is the first half of the sedentary families I am going to discuss. Next month I will finish discussing the sedentary polychaete families, and possibly (space permitting) start to discuss the errant polychates (which will also probably take 2 articles). In the meantime, if you are dying to know more about polychaetes, Ron Shimek's Aquarium.Net article Segmented and Vermiform, it's a way of life has some great information on polychaetes that I have not covered (e.g., how exactly do feather duster worms feed), and includes a several pictures and a number of links to other pages of interest on the web -- check it out if you missed that issue of Aquarium.Net.

The cluster duster worm, Sabella melanostigma . Through asexual reproduction, these worms may become very common in some reef tanks. Although not particularly obvious in the picture, the darkly pigmented "eyespots" on the tentacles of the crown give this worm its name.

Literature Cited:

Brusca, R.C., & G.J. Brusca, 1990. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass. 922 pp.

Ruppert, E.E. & R.D. Barnes, 1994. Invertebrate Zoology, 6 th Edition . Saunders College Publishing, Harcourt Brace College Publishers, Orlando, FL. 1056 pp.

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Last modified 2006-11-19 01:26