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Reefkeeper's Guide to Invertebrate Zoology

Reefkeeper's Guide to Invertebrate Zoology:

Part 12: Generally Benign Errant Polychaetes.

By RobToonen

Before I get into this article I want to clarify something that I mentioned in an earlier article. A recent post to the reef-list server asked a question regarding "bristleworms" to which one reply included a pointer to Mike Noreen's Bristleworm fact sheet and mini FAQ . In Mike's FAQ, he refers to "errant" and "sedentary" polychaetes without definition or explanation, and it was obvious from the replies of a couple knowledgeable hobbyists that these archaic terms are a bit confusing. For example, Nathan Cope posted the following comment in reference to someone's questions about Mike's FAQ:

"It uses a bit of emotional wording in some cases which may cause some people to focus too much attention to minor points, though. For example, Mike talks about "sedentary" and "errant" bristleworms. "Errant" can mean "journeying" and it can mean "erring". I don't know which meaning Mike intends, but I know most people will take the negative meaning, which is unfortunate because he says that 99.9% of the worms are harmless."

Well, I have not only mentioned these categories, but have used them as the basis for organizing my articles on polychaete families, so I thought I would send a reply with a pointer to where I defined the terms. I looked back to find where I had defined my terms but could only find the following statement in Part 9 :

"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.""

I moved back to Part 8 and searched for both "errant" and "sedentary" only to find that I had not even used the terms in the previous article (I did mention them in Part 7 , but only make a statement similar to that quoted from Part 9, above -- that's what I get for trusting my feeble memory rather than double-checking what I wrote last time...). I apologize for that, and will add a little aside here to clear up some confusion about these terms.

So let me try to cover what I thought I had in that "previous article" here instead. These terms were originally used to classify the Class Polychaeta into Subclasses or Orders (check out Part 7 if you can't remember how worms are classified) based on their ability to move. Those polychaetes that had mostly active lives, roaming over the sediments in search of food, were thought to be related and therefore classified together as the "Errant" polychaetes. Conversely, those polychaetes that spent most or all of their lives in a single tube or burrow, waiting for food to come to them, were thought to be related and classified under the "Sedentaria." Worm biologists long ago realized that this classification was incorrect, and that the mode of living did not necessary have anything to do with relationships among the groups. As people have studied these groups more carefully and with more sophisticated techniques, it has become obvious that many of the groups once thought to be closely related are in fact not closely related at all, and some groups, originally classified as a different Phylum (e.g., Pogonophorans and Vestimentiferans), are in fact related to other, more mundane groups of worms.

If we know that these classifications are wrong, and we know that the worms in the two groups are not really related to one another, why the heck do people keep using the terms? Well, there are two primary reasons for that. 1) It is a simple and obvious way to break the worms into functional ecological units that make sense to discuss, and 2) there are a group of people who firmly believe that similarity in appearance indicates some sort of relationship between groups. These people point to the fact that physical similarity between groups is an obvious and simple indicator of affinity to membership in that group (as an extremely obvious example, lets say worms with a calcareous tube). This school of thinking, members of whom are generally known as Morphologists, is very old, and there is no question that good morphologists are extremely knowledgeable about the animals on which they work, and have contributed a great deal to our understanding of the natural world. The problem comes when different lines of evidence point to different relationships among the groups. For example, the fact that deep-sea forms (the Pogonophorans and Vestimentiferans) have quite different body shapes and structures suggests that they are not closely related to the rest of the polychaetes, but DNA evidence conclusively places them as members of the polychaetes, most likely as close relatives to the Terebellids (spaghetti worms). The question of which evidence to believe is not straightforward. Many people believe that DNA is subject to more random similarity than is morphology because there are only 4 base pairs from which DNA is composed.

However, there are generally two responses to that point of view: a) physical appearance is subject to frequent and rapid change, and mode of living has been shown to result in selection on two unrelated groups appearing more similar than two related groups with different modes of living (as an obvious example, lets say free-living versus tube-building polychaetes), and b) we can almost always use physical similarity to differentiate groups once we know what the groups are, but until we know exactly what the groups are, which physical characters should actually be used to distinguish between those groups is the opinion of an expert in the field . Many younger scientists find it difficult to rely solely on the opinion of an expert as to which characters are reliable for determining relationships and which are similar due to an "accident" of natural selection. In general, such researchers have turned to what they consider a more objective metric of relatedness, namely molecular biology.

I must point out that obvious characters to indicate relatedness have generally been found to support the molecular data once the groups are identified (even for the Pogonophorans and Vestimentiferans mentioned above), and the work of many, if not most, good morphologists has been confirmed by the recent work of molecular systemetists (biologists who study the relationships among groups of animals). However, the exercise of selecting which physical traits of an organism are useful in determining relatedness is difficult without personal bias coming into play (if the data tell us something that we decide is "wrong," we go back and re-examine the group to find out where we made a mistake but don't do this if we get the answer we expect). This is hard to do objectively without foreknowledge of what the groups actually are; for example, looking at a group of animals, anyone can SEE that all cats (whether a house cat or a lion) are more closely related to one another than they are to any dog. The hard part is trying to select physical characters (e.g., skull characteristics, muscle and bone attachment sites, claw characteristics and placement, etc.) to use as an objective method of classifying cats and dogs once we already "know" that cats are related to one another and not to dogs. Those preconceptions may in some cases be wrong (in our calcareous tube worm example above, consider what would happen if our "expert" chose to use the presence of the calcareous tube as a physical trait to separate some polychaete worms from others), and the traits chosen to classify the animals are therefore biased by the observers impression of relatedness. In general, but particularly among groups for which there is considerable debate among morphologists or for which characters are lacking or conflicting, molecular systematics seems to be gaining more support among the scientific community at large as a method of determining how groups of animals are related to one another, and therefore how they should be classified taxonomically (the hierarchical naming system developed by Linnaeus that is used by scientists to classify all living organisms).

OK, now you may be asking yourself what I mean by "related" in this context. Well, relatedness is a term that is a often used, but the definition is a little slippery, because it doesn't necessarily mean the same thing all the time. In general, when biologists talk about relatedness, they mean a common ancestor and all the groups of animals derived from that common ancestor. Obviously, that definition, then, changes depending on what level of the taxonomic hierarchy you are talking about. If I am talking about the genus Lysmata, then ambionensis and wurdmanni are "related," but if I am talking about Crustacea, L. ambionensis is "related" to everything from copepods to crabs.

Anyhow, with all that aside, I'll get back to the focus of this article and continue to talk about poychaete worms. In the last article, I tried to introduce you to all the polychaetes which are likely to pose a potential threat to the well-being of your reef tank. Although the group that I discuss in that article have the potential to be harmful, I will stress (yes, yet again!) that the vast majority of polychaetes encountered in a reef tank are not only harmless, but tend to actually be beneficial. I have only seen a couple of reef tanks with the particularly troublesome and potentially dangerous "fireworms" (e.g., the dreaded Hermodice carunculata ) in them. All the same, as hobbyists, we are responsible for the health and well-being of our tank inhabitants, and should generally be on the look-out for any trouble-makers, and some polychaete worms fall into that category.

The worms that I plan to discuss in this article are those that I list as "generally benign." I don't mean to imply that none of the members of these families have the potential to cause harm in your tank any more than listing the last set of families as "potentially dangerous" implies that any of those worms will wreak havoc in your tank. I have said before, and I will repeat that there are no hard-and-fast rules in biology, and every individual is likely to be a little different or even behave differently under different conditions. My grouping of these sets of worms is based on my experiences with them (from observations in both the aquarium and the field), and my estimation of the probability that a given polychaete is likely to cause problems in a reef aquarium. The following polychaetes are simply those that, despite the potential of some to be predatory, are simply unlikely to cause many noticeable problems in the average aquarist's tank. Once again, I will reiterate the warning that it is always a good idea to keep a close eye on any animal you think may pose a potential threat in your tank, and if you see any evidence that critter is actually causing damage, I'd suggest removing it (check out Part 8 for some suggestions on removing troublesome polychaetes).

I know that it is quite difficult to identify polychaetes, even with detailed descriptions (heck, if it were easy, it would be all figured out by now <gg>!), but this page includes some diagrams of the prostomium ("head" or "nose" of the worm) shape for a variety of families that should help you decide to which family that mystery worm in your tank belongs. The prostomium diagram page is part of a larger site of the Polychaetes of Singapore that includes EPIC-online (an interactive polychaete family ID database -- E asy P olychaete I dentification C lassification) that may help you identify some mysterious polychaetes. Although the chances are very slim that a given worm in your tank is from Singapore, EPIC can at least help you to decide to which family the worm belongs, and then you can check either on their site, or back here, to see whether or not that particular group is likely to pose a threat to your tank or not. The Polychaetes of Singapore site is useful both in terms some general information regarding the morphology and identity of various polychaete families, and also some basic information on the general biology and ecology of each group (much as I am trying to present here).

Syllidae (sill-id-ay)

Syllid polychaetes span the entire range from quite striking (such as the Ambylosyllis pictured here) to completely drab and nondescript.

Amblyosyllis formosa an attractive syllid polychaete. Note the long dorsal cirri (the hair-like extensions from upper surface of the parapodia -- the equivalent of legs for a polychaete) , which are generally held close to the body when moving about normally, but are erected in response to a threat.

In general these worms are relatively small (few exceed a few cm), and some are even interstitial (living between the sand grains that compose the sediment). They are found on a wide variety of substrata from fine, silty sediments to rocky intertidal zones and even pelagic species. Although some graze on diatoms, most are active predators on small invertebrates, and like several families discussed in the last article, if you are trying to culture copepods, amphipods or other small invertebrate prey for your Mandarin "Goby" ( Synchiropus splendidus ), you may end up having a difficult time doing so if you also have a large standing population of syllids in the aquarium. There are two primary reasons that these worms fall into the "generally benign" category rather than the "potentially harmful" category: 1) they tend to be much smaller than the phyllodocids and nereids described last time ; and 2) their pharynx is armed with only a single tooth, or a ring of tiny teeth for prey capture or piercing, rather than a muscular pair of jaws like the aforementioned groups. Even those worms that prey on large animals (e.g., sponges, tunicates and hydroids), generally pierce the body and suck out some of the "juices" before moving on. As such, these worms could be considered more parasitic than predatory, because their feeding rarely results in the death of these large prey items. Once again, I'll reiterate that groups such as the nereids and phyllodocids are not necessarily dangerous nor are groups like syllids completely risk-free: its just that large predatory forms such as nereids tend to have a higher potential to be troublemakers, and should be watched if they make their presence known (hence I placed them in the "potentially dangerous" category).

Most syllids brood their young, although there are free spawners as well. The syllids are one of the groups most likely to produce free-swimming epitokes (sexually reproductive form of the worm -- see Part 8 for more info on epitokes) within your tank. A clumsy-looking bloated worm swimming around your tank, often holding a brightly-colored mass of eggs beneath the body, is most likely an epitokous stage of some polychaete family (most likely a syllid, nereid or eunicid). The brooding species often release demersal (capable of swimming, but not very good at it -- so they tend to spend most of their time on the bottom) non-feeding larvae that generally survive quite well in a tank. The free spawners, on the other hand, tend to produce actively swimming larvae that are generally consumed by one of the reef inhabitants or skimmed out of the water column before settlement and metamorphosis to the adult body form can occur.

Lumbrineridae (lum-brin-ear-id-ay)

Lumbinerids are typically long, thin polychaetes that, at least superficially, resemble tiny earthworms. The worms lack any head appendages, and have relatively reduced parapodia. They are likely to be common inhabitants of both "live rock" and "live sand" based systems, because they crawl through any small crevices, such as cracks in rocks, algal mats and holdfasts, hydroid and coral colonies, etc. in search of food. In addition many species are burrowers in marine sands and muds, and could be a common import among live sand communities. The members of this family are very diverse in their modes of feeding, and there are species that are specifically carnivorous, opportunistic scavengers, deposit feeders, detritivores and algal grazers. Although some species within this family could be preying on small inhabitants of your live sand bed, the vast majority of these worms are actually beneficial. As with most of the groups we have discussed in the past, there is no simple generalization that can be made about the feeding modes of these animals, but they all tend to be relatively small and innocuous to most reef inhabitants.

In my sandbed, and that of others I have seen with similarly dense polychaete populations (on the order of 40,000 per square meter), the majority of those worms are lumbrinerids (together with nephtids, opheliids and tiny nereids these form the majority of sand fauna visible to the naked eye in most sandbed tanks I have seen). These burrowing forms primarily make their living by consuming sand particles and digesting away the bacteria and bacterial by-products that coat the individual sand grains. In addition to stimulating bacterial growth, these worms are also very useful for turning over sediments, which both increases the general oxygen content and tends to prevent clumping of the calcareous sand. Despite the fact that some members of this family are capable of consuming tiny prey, most are grazers on algae or detritus, and the benefits of including these worms in a tank with a sand bed will far outweigh any potential risk of including a few that will eat the odd rotifer, nematode or acanthocephalan (see Ron Shimek's As the Worm Turns article, or my Rotifers article in the archives for some more info on these groups) in your tank.

These worms are also likely to reproduce in the aquarium once established, because they lay yolky eggs that develop into benthic (remaining on the bottom) larvae that either crawl about on the sand surface or are brooded within the adult burrows. Because there is no planktonic stage, these worms can quickly populate a suitable sand habitat if the conditions are right and organic detritus and benthic algae are readily available (a common feature of most deep sandbed tanks).

Polynoidae (poly-no-id-ay)

These worms are best known for having a series of "scales" ( elytra ) that cover the back of the worm. It is these elytra that give this group the common name of "scaleworms" (together with a couple of other families, but the Polynoids are the most common and best known of the scaleworms). The "scales" are actually a modified dorsal cirrus (the "hair" that sticks up off the parapodia and is so obvious in the Ambylosyllis pictured above. I know it's been a while, but if you've forgotten my earlier discussion of polychaete anatomy, you can look back to my introduction to the polychaetes in the archives, or check out a nice description (with illustrations) of polychaete morphology here . The elytra are presumably defensive, and are often shed or lost during stressful interactions. Therefore, although the presence of elytra is a good character to help you decide that something in your tank is some sort of scaleworm, the absence of scales does not always rule out the scaleworms as a possible identification (although a scaleworm that has lost all of its scales is an unhappy worm, indeed).

Halosydna brevisetosa , a common polynoid scaleworm from the Pacific Northwest coast of the US. This species reaches about 5cm in length and is found in clumps of tubeworms, kelp holdfasts and the like, where they prey on other small invertebrates, including other polychaetes. Although they are commonly free-living, these worms are also frequently commensal with terebellids (spaghetti worms).

In general these worms are relatively short, although they can be quite wide for the body length, and most are somewhat flattened along the dorsoventral axis (top-to-bottom, like someone stepped on them). Although most are short, at least one Antarctic species, Eulagisca gigantea , reaches a body length of about 20cm, and is nearly 10cm wide! They have a well developed pharynx with a single pair of jaws, and most are cryptic (tending to hide in rock crevices, under stones, in algal holdfasts, etc.) scavengers and predators. Again, although these animals can be predatory, they are unlikely to attack large prey, and in general should not pose a threat to the vast majority of your tank inhabitants.

Lepidonotus melanogrammus , a particularly attractive polynoid scaleworm from South Africa crawling around on the surface of a botryllid tunicate.

Although the majority of worms in this family are oportunistic scavngers, there are a number of very interesting exceptions. There are a variety of commensal (living in close association with another species) forms as well (e.g., Arctonoë , Halosydna , Harmothoë ). The best known among these forms are those worms that typically live among the tube feet of echinoderms (see Ron Shimek's Mutualisms article in the archives for a photo and description of Arctonoë ). I don't know if any of these worms will ever make it to a petshop, because I suspect that the collectors, shippers and wholesalers are likely to remove the worms if they are spotted along the way (I have only seen one of these animals in a local petshop one time, and it was thrown on the floor and stepped on by the store owner immediately when noticed), but they are harmless and interesting additions to a tank. The worms live on the undersurface of sea stars, where they typically live among the tube feet within the ambulacral groove (the groove along the center of each arm into which the tube feet can be withdrawn when disturbed), although some even make forays into the mouth of the star. Living on the underside of the sea star (and occasionally some sea cucumbers), the worms are protected from most predators (not much likes to eat sea stars because of their tough skin and defensive chemistry), and are also fed without having to come out of their hiding spot. When the sea star finds food, it everts it stomach to at least partially digest the morsel externally before slurping the digestion products back into the body (check our Ron Shimek's Sea Star article for more info on echinoderms). Sea stars are very messy eaters, and while the star is digesting and then slurping up its food, the worms crawl up to the edge of the stomach and eat any food they can safely reach. A few worms don't take much food from the star, and the star benefits from the presence of the worms because they tend to bite snails and other sea stars that try to attack their host (again, see Ron's Mutualisms article for more info on this and other fascinating relationships among marine critters).

Nephtyidae (nef-t-id-ay)

Although these worms are unlikely to be encountered in a traditional "Berlin-style" reef tank, with the rapid gain in popularity of "live sand" for plenum or "Jaubert-style" tanks, it is becoming far more likely that nephtids will be encountered by hobbyists. Nephtids are common inhabitants of marine sands and muds, and therefore I expect that they will be frequently imported for introduction into "live-sand" based reef systems. Members of this family are often large, and tend to have large, well-developed parapodia and eversible jaws which they use for burrowing through marine sediments where they digest whatever organic particles they ingest while burrowing. Although their jaws are fairly short (note the short bulbous pharynx on the worm pictured here, compared to that of the glycerid pictured in the last article ) for a predatory species, the well-developed jaws can be used to prey capture, but because these worms rarely emerge from the sediments in search of prey (despite the fact that they are reasonably good swimmers when removed from the sediments), they are unlikely to cause any real problems in a reef aquarium.

Nephtys californiensis , a common nephtid worm found in sandy sediments along the coastline of the Pacific Northwest. Although this worm superficially resembles a nereid worm, the jaw apparatus, which is one of the primary identifying characteristic for most polychaete families, is completely different.

They may capture and consume many of the other common inhabitants of "live sand" but they are unlikely to consume any of the tank inhabitants that you as a hobbyist are interested in observing, and need be no cause for concern unless they become very dense or very large (gee, where have you heard that before?). Although they may be predatory (really they should be classified as selective omnivores), their burrowing action still helps to maintain a well-mixed and aerated layer in your sandbed, and because they are relatively inefficient predators (at least compared to sand-sifting gobies or the like that can turn over your tank faster than the sand-dwelling critters can possibly reproduce) these worms can help by both stimulating growth of the infauna and aiding to turn over your sandbed. Opheliidae (o-feel--id-ay)

Ophelids are a pretty variable group of worms, and a single species photograph simply does not provide justice to the diversity of body forms or reproductive modes among them. The worms vary from short and thick to long and thin, but they tend to be burrowers in marine sands and muds (although some are capable of efficient swimming, the majority are burrowers). Some produce feeding larvae, while others spawn yolky eggs that contain all the nutrients necessary for larvae to complete development into the adult body form. In general, most of these worms free spawn gametes into the water column where fertilization and larval development takes place, so the propensity for these worms to reproduce in an aquarium is highly variable depending on the species in question. Fortunately, however, these worms lack an armed pharynx (they have a pharynxy, but it lacks hardened jaws), and are almost entirely direct deposit feeders (they ingest and directly consume organic detritus). To the best of my knowledge, these worms are entirely harmless and are very beneficial to any "live sand" based tank.

Opheliids are well-studied in many regions where they form an important and useful portion of the sand community. Dissections of these worms show that they are generally full of sand and mud that they have ingested during burrowing, and that they preferentially ingest sands rich in organic particles (primarily organic detritus and any dead critters, such as harpacticoid copepods, rotifers, kinorhynchs and acanthocephalans - again check out Ron's As the Worm Turns article for more info on these groups). Aphroditidae (afro-dite-id-ay)

I wish that I had a picture of a "sea mouse" to include in this article, but I have never had the presence of mind to take a picture when I have had one in the lab. I'm not sure why, because they are pretty amazing creatures. The setae of this animal are long and often cover the entire dorsal surface of the body to make an almost "felt-like" covering. They are actually scale worms of a sort, because they have elytra (scales, like the polynoids above) under the dense mass of setae on their back, but you can't really see them, because they're covered by the long hair-like defensive setae.Like the polynoids, sea mice breathe by creating a respiratory current along the dorsal surface of the body beneath the scales. This breathing current allows them to be almost completely submerged in the sediments with only the fuzzy dorsal surface sticking out of the muddy bottom. To make them appear even more clumsy, they produce a copious amount of mucus that tends to stick in the setae, and so they are not always very obvious. Seeing one of these animals in the field is rather like seeing a snot-covered bottlebrush crawling through the mud -- they are one of the least "wormy-looking" worms of which I know.

The slow and dumpy appearance is a little misleading as to their docile nature, however, because these worms are armed with those long setae on their back for a good reason. When disturbed, sea mice generally erect their setae in a defensive posture that provides little opportunity to reach the body without going through the spines. In some species the spines are associated with poison glands (like those of the dreaded "fireworms"-- Fam. Amphinomidae - from Part 11 ), while in others the setae are tipped with nastily hooked barbs, either of which are capable of inflicting a painful sting.

So, after having said that, you may wonder why on Earth I included them in the "probably harmless" category. Well, aside from the fact that I just happen to think that they are very cool animals, I really don't think that most sea mice are going to a problem in a reef tank. Aphroditids generally live in and on soft muddy bottoms where they slowly bulldoze their way through the sediment in search of organic detritus and small infauna to consume (although some, like Laetmonice moluccana , are found within coral rubble and under coral heads on shallow patch reefs). Most members of this family lack the jaws to capture any large animals in the tank (although species like L. moluccana found in coral rubble fields tend to be carnivorous on small invertebrates rather than primarily detritivorous like the sand-dwelling species), and the setae are only really a threat if you are unaware of the risk. If you are careful when handling one of these worms (always scoop it up from underneath), and don't poke at it with your finger-tips, it is unlikely to ever become a problem in an aquarium. In fact, they are typically beneficial from two standpoints: 1) they are great sand stirrers as they slowly make their way across the sediments stirring them and consuming small infauna (again, these are the infaunal groups like harpacticoid copepods, rotifers, kinorhynchs and acanthocephalans) and organic detritus, and 2) they are bound to be a great conversation piece when noticed in your tank. I can't say that I've ever seen them offered for sale in any local pet shop, but there are a number of tropical genera that could easily be imported (and likely are by accident from time-to-time). If you have a sandbed tank, and are feeling a little adventurous when/if you ever see one of these weird worms in the LFS, you might want to give it a try.... Arenicolidae (air-en-ick-coal-id-ay) These rather thick fleshy worms are typically referred to as "lugworms" and live in sandy, gravelly or muddy sediments. Although these worms would rarely ever be found in a typical "Berlin-style" reef aquarium, with the rapidly gaining popularity of "live sand" based tanks, I suspect that they will become a more common feature of "natural reef" aquaria.

Because these worms produce nonfeeding larvae that are only briefly planktonic, they are a good candidate for reproduction in the aquarium. There are some species that free spawn (release their sperm and eggs directly into the water column), some that produce benthic egg masses (these are often likened to large "bags of snot" by our students here at UCD - the local species produces egg masses as large as 15 cm in diameter!), and some brood their offspring within their burrows. The interesting thing about the young of these worms is that the larvae settle and produce a mucus tube in which to live as soon as they are old enough to do so. The young worms then emerge to feed on fine detritus. As they grow, they develop an eversible proboscis (basically a tongue that they can stick out), and then abandon their tubes to take up a burrowing lifestyle.

Once they begin burrowing, they maintain a more-or-less J-shaped burrow through which it constantly pumps water; this both irrigates its gills and collapses the muddy sand at the end of the burrow (thus resulting in a J-shaped rather than a U-shaped burrow). The head is directed towards the "blind" end of the J-tube and the anus is directed upwards towards the well-maintained opening. The worm feeds by eating the collapsed sand in the burrow (using it's eversible proboscis), and digesting out the organic matter. When the worm has digested the organic matter, it backs out of the tube and defecates the undigested sand onto the surface around its burrow. This leads to a characteristic pattern of a sunken depression without any obvious hole at one end of the burrow and an obvious and well maintained hole at the other end. This hole is typically at the upper edge of a mound, which can range from a simple pile of sand ejected from the worms burrow, to a discrete "rope" mound of fecal castings lightly held together by mucus secretions from the worm.

Abarenicola pacifica . This worm is common in most every bay from central California northward, and can play an important role in sediment turnover within these embayments. Note the bright red pairs of branched gills along the sides of the body.

An interesting aside here is that all the invertebrate zoology texts which I own (Barnes 1987, Kozloff 1990, Brusca & Brusca 1990, Ruppert & Barnes 1994) have reproduced an old drawing in which the artist mistakenly drew the current in the wrong direction to describe the feeding of the temperate lugworm Abarenicola pacifica (pictured here) . Remember back in the sponge article when I discussed how sponges get a hand in pumping water through their bodies by the Bernoulli Principle? (if not you might wanna go back and read that section) Well, the shape of lugworm burrows also lead to some assistance in pumping via the Bernoulli Principle. The fact that these worms produce a mound at one end of the burrow causes to lift being generated around that hole when water flows past the opening, which will pull water from within the burrow without requiring any active pumping of the worm. The worm does help, however, and the active pumping leads to more rapid water flow through the tube, and facilitates tube collapse at the anterior end, thereby allowing organic matter to sift down to where the head is buried.


Well, this series may have been more information about worms than most people wanted to know, but I hope that it has been useful. There are many other families of polychaetes, and I have given only a thumbnail sketch as an introduction to these groups, but I think that I have hit most of the highlights and covered all the groups of worms likely to be encountered by the average aquarist. I also hope that together with the various articles Ron Shimek has written on the subject, we have managed to convince you that general hysteria over the sighting of a "bristleworm" in your aquarium is not only unnecessary, but also misguided. Polychaetes are likely to be present in every reef aquarium, and far more are benign or can even be beneficial, than are potentially dangerous.

Next time, I'll move on to start covering the molluscs (snails, slugs, clams, squids and octopuses among others), which will take even more time (and articles) than has the annelids, because there is such remarkable diversity among the molluscs.

Literature Cited:

Barnes, R.D. 1987. Invertebrate Zoology, 5th Edition. Suanders College Publishing. New York, NY. 983 pp. Brusca, R.C. & G.J. Brusca. 1990. Invertebrates. Sinauer Associates, Inc. Publishers. Sunderland, Mass. 922 pp.

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

Ruppert, E.E. & R.D. Barnes. 1994. Invertebrate Zoology, 6 th Edition. Saunders College Publishing, Philadelphia, PA. 1056 pp.

Shimek, R.L. Various hyperlinked articles included within the text.

Toonen, R.J. Various hyperlinked articles included within the text.

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