A Spineless Column by Ronald L. Shimek, Ph.D.

Spaghetti and Hair Worms... What's in a Name?

What's In A Name? Indeed...

Shakespeare, in Romeo and Juliet, penned, "What's in a name? That which we call a rose by any other name would smell as sweet." Maybe so, but I swear some reef aquarists would see the thorns, call them bristles and say that it was a "bristle worm." One of joys of having a regular column, such as this one, is that periodically I can address subjects near and dear to my heart. Probably more problems in our hobby are caused by incorrect and improper communication than by any other root cause. We are both blessed and cursed by using English as our medium of communication: blessed because it has the largest vocabulary of any language, allowing us to be very precise; cursed because we seldom use this precision, resorting instead to the use of sloppy catchall terms, causing us no end of grief. This is best seen in the use of both scientific nomenclature and common names.

Reef aquarists often like to use the taxonomic binomial nomenclature or "scientific names" to identify the organisms in their displays. Unfortunately, this use has become more of a mis-use in the case of many, if not most, of the invertebrates found commonly in marine aquaria. A scientific name is useful because of two things: first, each animal name is unique and, second, each name is based on a naming system that requires examination of specific characteristics. Unfortunately, aquarists tend to learn to associate a scientific name to go with a certain organism without learning the characteristics that go with that name, or in many cases without ever really "observing" the animal. In doing so, they effectively turn the scientific name into just another common name, and have no real idea how to discriminate between any two species. When used in this manner, these "scientific" names have no real meaning or utility, and are really no better than any other common name. Unfortunately, the use of such names has another interesting characteristic. It gives the user an "aura" or "air of authority." In other words, it makes the user sound like he or she knows what they are talking about. This is, indeed, a pity as such an air of authority may cause a significant amount of ‘mythinformation' to enter the body of reef-keeping lore.

Probably the worst cases of this nomenclatural fog occur with the stony corals; very precise and specific names are used by many hobbyists to describe their colored calcareous sticks. With the stony corals, in many cases, it is simply impossible for non-specialists to identify the organisms to species. Indeed, without the resources of large libraries and large museum reference collections, it may be impossible for anybody to identify the organisms in question (see the articles in Reefkeeping where Eric Borneman discusses this problem: Reefkeeping.com April 2002; Reefkeeping.com May 2002). In this particular case, I suggest that the rational solution for both specialists and aquarists alike may be a formal revision of just what a "name" implies for these animals. However, such a revision isn't here yet, and given the inertia in both science and this hobby, I don't really think that it is likely to occur.

There are other animal groups with significantly troubling issues with regard to naming and identifying species. Interestingly enough, in many cases, the root causes of the problems in these groups are just the opposite of what is found in the corals. Part of the real problem with identifying stony corals is that they are organisms built upon a simple and basic body plan. Corals are comprised of polyps; hollow cylinders of tissue with a single opening at one end of the animal to the internal digestive region. This opening is surrounded by a fringe of tentacles. These polyps secrete, and sit in, a calcareous cup. This simple body plan doesn't provide a lot of characteristics which are useful in distinguishing one type of coral from another. At the visual level of structure, there simply are not a lot of different ways to make a coral. Unfortunately for both hobbyists and taxonomists, much of the diversity of corals appears to occur at the genetic or chemical level, and these are not at organizational levels where differentiation is easily seen by people, even if it is both important and easily recognized by the corals (Romano and Palumbi, 1996).

Just the opposite problem may occur with some other animal groups. These groups, such as the segmented worms, and the crustaceans, may have so many external characters that no two authorities will be in agreement on which to consider as the most important distinguishing characters for either groups or species. Often finely detailed and specific character descriptions have to be used to discuss the differences, and neither hobbyists nor most researchers either can, or care to, spend the time examining these definitive characters. With many of these animals, it is often the common obvious characters that everybody uses, with the understanding that this often results in the grouping or "lumping together" of several similar species.

Although aquarists like to pretend that they are being precise in distinguishing their coral animals, they care less about other animals, often seeming to be incapable of distinguishing quite distinct animals from one another. This malady is probably best expressed when the aquarist in question is examining a polychaete annelid worm, although snails come in a close second. In the case of the worms, all 10,000 species (more-or-less) are "bristle worms," and in discussion after discussion with hobbyists the general consensus seems to be that all bristle worms are the same.

This is somewhat understandable, as the most common visible polychaetes or bristle worms found in hobbyist systems are fire worms, mostly in the genus Eurythoe, and these animals really seem to have specialized in large and evident bristles. One of the characteristics of worms everywhere in the aquatic environment is that they are eaten by fish; basically a worm in water is simply a cylinder of flesh wiggling along and waiting to be eaten. Fire worms have put an end to that practice, as far as they are concerned. At some point in their evolutionary history, one worm or group of worms developed long or somewhat venomous bristles that conferred a survival advantage to their offspring. Such an advantage from predation can often become very elaborate as a positive feed back loop gets set up: as the prey becomes more venomous or hard to eat, one or a few predators become adapted to detoxifying the venom or adept at utilizing a behavior that allows them to get around it The prey adapts to this by developing yet nastier defenses, and the predator then has to adapt by devising ways around the defenses. This is often referred to in the ecological literature as the "Co-evolution of predators and prey," and it results in prey that are often very well protected from most predators, with only one or two highly specialized predators able to eat them. This appears to have happened with the fire worms. These worms are no longer fish bait. Some shrimps, such as Stenopus hispidus, the banded coral shrimp, may eat them, but few fish will try to eat one more than once. Their bristles are calcareous, hollow, filled with a mild venom, and barbed. They are "designed" to break off in the predator's mouth and work their way deeply into the tissue releasing an irritant all the while. They are NOT designed to kill the predator, but rather to "impress" it, so that it learns not to attack the worm. Top BOGO free deals are always available on Publix weekly ad. To make sure the predator realizes the potential problem, the bristles are advertised by being strikingly obvious. Not surprisingly, most fish leave fire worms alone after the first encounter or two.

The presence of the tufts of such large and evident bristles on the common reef aquarium scavengers have given them the name of "bristle worms." This is a perfectly good and very useful common name; it is certainly as valid in this context as any scientific name. Unfortunately, instead of being confined to this one group of worms, the term has become all-inclusive for all mobile worms found in aquaria. Some of these other worms, not as benign as the fire worms, may cause serious problems in tanks. Large eunicid polychaetes, which look superficially like fire worms, may eat fish, and some other large worms may attack clams. If these other predatory worms raise a bit of havoc in a tank, and are discovered in the act, the aquarist claims that "bristle worms" have done the damage, and in the process condemns all bristly worms. Other aquarists upon reading such an account of death and destruction may spend a lot of time and effort to removing beneficial fire worms from their tanks, much to their system's detriment. Of course, neither eunicids nor clam-eating worms have the large and evident tufts of bristles, and even a cursory examination should have shown these differences. However, both eunicids and clam-eating worms are, of course, worms. Therefore, they must be bristle worms, and therefore all bristle worms are bad. If you agreed with this logic (or even if you didn't), you should read a short essay by Joel Cohen, titled, "On the nature of mathematical proofs," which shows, rather nicely, that Alexander the Great was white, had an infinite number of limbs, and did not exist. (Baker, 1961) (this book is out of print, but the essay is available on line at: www.cs.berkeley.edu ).

Common names may be as useful as scientific names, provided they are consistently applied and, of course, therein lies the problem. In the reef aquarium hobby, no animal names – be they scientific, common, vulgar, or vernacular – are consistently applied. There appears to be a set of rules sworn to, deeply understood, and righteously upheld by many aquarists as they began the hobby: "Thou shall not use the same name consistently for all individuals of the same species, nor shall you restrict the use of that name to only one type of organism. Additionally, thou shall not use any common name of an object for that object for which it was created." This latter rule brings me to the titular subject of this essay: spaghetti worms.

Spaghetti, Vermicelli, and Hair Worms

In the naming of animals, there are a series of terms used which have meanings specific to their use within the naming system, regardless of the meaning of such terms outside that system. These terms form a hierarchy of names, from the smallest or most exclusive unit, called the deme, to the largest and most inclusive unit, called the domain. Generally, in the reef hobby, the smallest unit we deal with is the species. There are a number of definitions of species, and really none of them are wholly satisfactory, but a species may be understood as "the biological unit." Similar species are grouped together in a Genus. Similar genera (the plural of genus is genera) are grouped into a Family. Similar families are grouped into an Order. Similar Orders are grouped into a Class. Similar Classes are grouped into a Phylum. Phyla are grouped into Kingdoms, and Kingdoms are grouped into Domains. At each level in this grouping process, the decision to group the various units together is arbitrary. Only the biological unit really exists, the others are there for our convenience and discussion.


Fire worms are grouped by zoologists with a large number of other similar worms into a group called the Family Amphinomidae. All families of similar worms are grouped into the Class Polychaeta. The Class Polychaeta has as one of its characteristics, the presence of many stiff chaeta or bristles. In fact the name, Polychaeta means "many bristles." Indeed, all the polychaetes, together – not just the fire worms – are often referred to as "bristle worms."

The Class Polychaeta is a large grouping, comprising an amalgamation of what is estimated to be well over 10,000 species. All of them are worms whose body is divided into segments, manifested on the exterior of the worm by the presence of rings or annuli of tissue. Each of these segments is a functional body unit and it is, generally, quite like the segment in front of it, and behind it, in the worm. In primitive worms, each segment has a pair of kidneys, one on each side, similar blood vessels in a similar arrangement, and a pair of lateral appendages or projections. Each of these carries the bristles. If you look closely at a fire worm in your system, you will see that each tuft of bristles actually arises on the top of one these lateral appendages. The gut passes through the center of each segment and is held in place by thin tissue sheets. The nervous system is also replicated in each segment, and the main nerves run down the bottom center of each segment. Except for the gut, the segments are hollow, and fluid filled.

This body arrangement, comprised of repeated, more-or-less independent, segments, is apparently a great way to make a worm. It is the body plan characteristic of the annelid worms, (of the Phylum Annelida) which includes the polychaetes, the earthworms or oligochaetes and the leeches or hirudineans. Within the most diverse group of these worms, the polychaetes, most of the differences between worms are due to changes in the front end of the worm. Some of these worms are very mobile animals, such as the fire worms, and such worms often have a series of sensory tentacles off the front of the worms. Some other worms don't move as much and often live in tubes that they secrete.

These tubes are often cylindrical and rather pipe-like, and they have a smooth inside coating of hardened mucus. The outside of the tubes is often covered with sediment or rocks and pebbles glued into it by the worm while it was being made. The worms that live in these tubes often have become quite different in shape from their more mobile cousins. As these worms can only move up and down in their tubes, the lateral appendages have gotten smaller and the bristles may be very small, appearing to be almost non-existent. There are many varieties of such tube-dwelling worms and they all have developed elaborations of the front part of the worm so that they may feed without leaving the tube. Probably the most familiar of such worms are the feather-duster worms that many aquarists have in their tanks. Another common worm of this nature has been called a "spaghetti" worm.

The name "spaghetti worm" predates the reef aquarium hobby by several decades. I first heard the term in my first marine ecology class at Woods Hole in 1969, and I am sure it wasn't coined then and there. In all cases, prior to recent usage in the reef hobby, this term refers to the worms in the family Terebellidae. The terebellids live in tubes in sediments, rocks, or debris, and do not normally leave the tubes. The only parts of the worm visible on the substrate surface are typically the white to slightly pinkish feeding tentacles elaborated from the head. The tentacles from larger worms are about the same size and dimensions as angel hair pasta, and give these animals their common name. The feeding tentacles extend some distance from the burrow and collect small food particles in a stream of mucus which is moved along by microscopic cilia found in a gutter on tentacle's surface. Arising from the head region are also two to four pairs of bushy, bright red gills. These are not generally visible outside the tube, but when the animal is feeding with the tentacles extended, the gills are located just below the opening of the tube.

Figure 1. Diagram of a spaghetti worm or terebellid polychaete removed from its tube. The head is shown in green, the thorax in yellow, and abdomen in orange. Gills are shown in red, while the "spaghetti-like" feeding tentacles are in white. The mouth is near the base of the tentacles. Modified from Brown, 1950.

Here is a link to a good drawing of a terebellid in a tube.

Terebellids are very complex animals, and have a body that may be divided into three regions, a head, thorax, and abdomen. The head is specialized for feeding and respiration, the thorax for moving in the tube, and the abdomen for the digestion of food. The small animals seen in aquaria seldom have tentacles more than a foot, or so, long. These animals have a body that is, at the maximum, about two to three inches long. However, there are terebellids that get much bigger. When diving in appropriate areas, it is not unusual to see tentacles radiating out of large terebellid tubes for distances up to 10 feet. These worms may have body lengths in excess of a foot long, be over an inch in diameter and may weigh in excess of one pound.


Figure 2. The white feeding tentacles of a terebellid or spaghetti worm always radiate from a burrow, tube opening or hole. These tentacles collect food particles from the surface of the sediment and convey it back to the worm's mouth.


Here are some links to terebellid information including some diagrams of the worms.




Here is a link to some information on many worms and other animals from a temperate sand flat habitat. This page loads very slowly, but be patient. Scroll down for information on terebellids and a picture of a worm removed from its tube.


Recently, in the reef aquarium hobby another type of worm has been being called a "spaghetti" worm. These are "hair worms" in the family Cirratulidae. Cirratulids have a much more uniform body than do the terebellids. Each segment looks much like the next, and while a head is present, the remainder of the worm's body is not divided into sections. There is neither a thorax nor an abdomen. Additionally, the cirratulids found in aquaria do not live in tubes but are found living free in the sediments below the surface. These are animals that may reach lengths of a couple inches and are, at most, about a sixteenth of an inch in diameter.

There are two types of cirratulids commonly seen in our aquaria, and they can be distinguished somewhat by their behavior. One type has a pair of long extensible feeding tentacles arising from the head region, and one type doesn't; otherwise, their bodies appear similar. Both types are found living in the sediments about a half an inch or so below the surface. Those with the feeding tentacles send them up to the surface where they roam over the surface in search of food. Unlike the spaghetti worms which have a multitude of tentacles, there are only two feeding tentacles per cirratulid, and they are bright red or brown, and normally have about the dimensions of a human hair. These tentacles will collect food by means of a ciliated gutter, similar to that found in a feeding tentacle of a spaghetti worm. Food particles are carried back to the cirratulid's mouth, located just below the surface of the sediment. The bodies of these worms are often oriented vertically and extend deeper into the sediment. In addition to the two feeding tentacles or palps, dozens of other similar tentaculate structures are found arising from elsewhere on the body. These are the bright red gills, and they extend upwards to the sediment surface and either wiggle in the water or lay on the sediment. Cirratulids without feeding tentacles look quite similar to those with the feeding tentacles, but lack the feeding tentacles, and they feed by swallowing sediment particles and detritus, digesting the organic components. These are found living deeper in the sediments, and are often found oriented horizontally.

Here are some links to information on cirratulids, including drawings:



Figure 3. A "hair-worm," or cirratulid polychaete. These animals do not live in permanent tubes. Note that the body is not divided into discrete regions and that the red gills are found all along the body. Compare with Figures 1 and 4. Modified from Kozloff, 1996.

Unfortunately, the cirratulids have also acquired the name of spaghetti worms. This was primarily due to some dealers who have incorrectly identified cirratulids and sold them as terebellids, and called them by the old common name of spaghetti worms. In addition to being quite dissimilar in appearance, they do quite different things in aquaria and in nature. The mistaken identity of the cirratulids means that they are being found in aquaria to the exclusion of the terebellids. Although both perform useful functions in aquaria, it would be nicer to have both rather than just the one type, as this would help facilitate the consumption and recycling of fine organic debris such as minute particles of detritus.

Figure 4. A cirratulid polychaete collected from one of my aquaria. Note the distribution of gills along the body and the presence of only two large feeding tentacles.

Here are some links to aquarist pages where cirratulids are mistakenly called "spaghetti worms" or terebellids.



It should be apparent that terebellids are easily distinguishable from cirratulids, and that the term "spaghetti" worm only makes sense when applied to terebellids. Unfortunately, as long as dealers and distributors refuse to examine their worms and correctly identify them, we are unlikely to be able to order any of these animals and be assured of getting what we order.

Gertrude Stein wrote, "A rose is a rose is a rose." And of course, that's what's in a name, because a bristle worm, isn't a bristle worm, isn't a bristle worm...

If you have any questions about this article, please visit my author forum on Reef Central.

References Cited:

Baker, R. A. 1961. A stress analysis of a strapless evening gown, and other essays for a scientific age. Prentice-Hall, 1963, Englewood Cliffs, N.J. 192 p. illus.

Brown, F. A. 1950. Selected invertebrate types. John Wiley and Sons. New York. 597 pp.

Kozloff, E. N. 1996. Marine invertebrates of the Pacific Northwest. 1st paperback edition with additions and corrections. University of Washington Press. Seattle. 539 pp.

Romano, S. A. and S. R. Palumbi. 1996. Evolution of Scleractinian Corals inferred from molecular systematics. Science. 271:640-642.

Useful References:

Fauchald, K. 1977. The Polychaete Worms. Definitions and keys to the Orders, Families and Genera. Natural History Museum of Los Angeles County, Science Series 28: 1- 190.

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

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


All photos and images courtesy of Ronald L. Shimek.

Reefkeeping Magazine™ Reef Central, LLC-Copyright © 2008

Spaghetti and Hair Worms... What's in a Name? by Ronald L. Shimek, Ph.D. - Reefkeeping.com