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

The Large Worm Turns…

Last month, I discussed some of the characteristics that are used in the identification of the so-called "bristle," or polychaete annelid, worms. This month I will discuss and illustrate some of the larger worms, those which routinely reach lengths of an inch or more and which live, or at least occasionally prowl, on the sediment or rock surfaces. Next month, I will deal with the greater diversity of smaller worms, and those worms that live, generally, within the sediments. In this column, I will describe both the most common and quite beneficial worms, as well as a couple of the nastier types of harmful worms found in marine reef aquaria. I had hoped to have a large number of good, and exceedingly flashy, photos of each worm to allow to a lot of details and variety for ease in identification. Unfortunately, I couldn't find a lot of good wormy photos that show the necessary discriminatory characteristics. Reefkeepers, it appears, largely do not photograph the worms in their tanks. I suppose they think that they have other, more beautiful, animals to spend their time photographing. In such they are remiss; some of these animals are indeed beautiful.

The Common Large Worms

Other than the decorative feather-duster worms, the majority of the larger worms found in reef aquaria are found within one quite cohesive and well characterized taxonomic group, the Family Amphinomidae. The primary and, quite obvious, definitive character for this group are the regularly spaced tufts of bright white bristles located along the worms' sides. These tufts are very easily seen, but, more to the point, they are also detectable by tactile means. The squishing method of tactile worm examination employed by many hobbyists has given these animals the apt common name of "fireworms."

Amphinomids are polychaete annelids that, using the language of the taxonomist, "have a distinct prostomium and they possess a caruncle, and have one to five antennae. Jaws are absent, although the pharynx has an eversible rasplike ventral pad. Notosetae are spinous protective setae, and the branchiae are in branching tufts (Fauchald, 1977)." Translated, the above jargon tells a reader that such worms have a distinct frontal region prior to the mouth (= a distinct prostomium). The head region extends backward in a sensory or glandular patch (nobody really knows what it is for) in the "neck" region (= possess a caruncle). Depending on the species, they possess one to five tentacles coming from the front of the head (= have one to five antennae). They don't have any hard biting or pinching or cutting jaws. The lower part of the throat region can be pushed out of the mouth, and on the inside bottom region of the mouth, about where a tongue would be, it has a roughened area that can act as a rasp (= pharynx has an eversible rasplike ventral pad). The uppermost patches of bristles on each side of each segment are spiny and protective (= notosetae are spinous and protective), and the gills (= branchiae) are found in branching tufts.

Figure 1. Eurythoe complanata, the large fireworm common in most reef aquaria. The animal pictured here was about six inches long, and about the diameter of a human finger. It appeared to be a purplish grey in the tank, but when properly illuminated the beautiful iridescence seen here became evident. A. The front end of the worm, with the head at the bottom. The labeled structures are explained in the text. B. The top of the body in the region of the head showing the caruncle. Differences in the caruncle are important in distinguishing species. Eurythoe is a very beneficial scavenger and is distinguished by its large size, and smooth caruncle. C. The head region closer to the substrate showing the sensory tentacles or antennae used to find food.

Fireworms are really common in reef aquaria. They probably account for ninety or more percent of the worms seen in reef aquaria. Most fireworms are scavengers in tropical marine environments, albeit a few of the about 120 species are predatory, and one or two are parasitic. The fireworms that are most frequently found in aquaria may be very abundant. Even a small aquarium may have thousands of them, and they are beneficial scavengers.. One species, common in nature but rarely found in aquaria, is of concern to aquarists. This species, Hermodice carunculata, is predatory on stony corals and gorgonians. Fortunately, individuals of this species may be easily distinguished and removed from the system.

Some fireworms often reach quite substantial sizes and aquarists are sometimes astonished to find that their tanks may contain worms over 18 inches (60 cm) in length, and with the diameter of a pencil. Most of these giants are probably individuals of the common Caribbean species, Eurythoe complanata, and are exceptionally diligent and beneficial members of the guild of scavenging animals found in our aquaria. Large Eurythoe individuals are adept at remaining out of sight in the interstices and internal cavities of reef aquarium rock work; it is often only when the tank is being remodeled or broken down that the big worms are found. These worms reproduce well in our systems and they are occasionally seen spawning copious amounts of pink sperm and eggs into the tank waters in a veritable vermous orgy. These spawning events produce a lot of gametes which are consumed by corals, soft corals and other filter feeding animals. Nonetheless, the odds of some reproductive success appear to be quite good, and Eurythoe seems to be able to maintain stable populations in aquaria indefinitely. The reproduction of the smaller fireworms that are also common in our systems, in the genera Linopherus or Pareurythoe, is less obvious, but they also can maintain quite stable and large populations in our systems. Most of the fireworms found in our tanks are in these latter two genera, and these animals occupy burrows in the sediments as well in holes in the rockwork. If not hassled by fish or crustaceans, they may be seen commonly during the day looking for food and doing their other wormy activities. These smaller species may reproduce more frequently by asexual than sexual means as indicated by the abundance of worms that are regenerating either front or back ends. As with the small starfish that are common in some reef aquaria, these worms reproduce asexually by fission, after which both halves produce the missing component.

Figure 2. An individual of a species of Linopherus. This is one of the common small fireworm scavengers in our tanks. Many tanks have thousands of these animals as a major component of the clean up crew. A. This worm was about an inch long. The white, venom-filled, protective setae are evident on each side. B. A close up of the head. Note how the caruncle and the gills differ from that of Eurythoe in Figure 1, and note the relatively large and evident eyes. C. These worms asexually reproduce by splitting in the middle, the rear portion regenerates a head as shown here. The front portion regenerates a tail end.

Fireworms are great scavengers, and even the bigger species are occasionally seen prowling around during the day, particularly after food has been added to the tank. Unlike most worms, they are well protected against fish predators. This protection is found in the obvious bright white bristle tufts. Most polychaetes have bristles made of chitin, a chemical with properties somewhat akin to cellulose, and the bottom bristles of fireworms are made of this material. The upper bristles, however, are made of something quite different, good old calcium carbonate, which accounts for their white color. The white color also functions to stand out against a dark background and acts like a sign telling the potential predators to stay clear. Such a coloration pattern is called aposematic or warning coloration and is common in well-defended animals (such as nudibranchs, skunks, or yellow-jacket wasps) in all habitats. These calcareous protective bristles have more than a warning function, however, and are protective as well as informational. They are barbed, hollow, and filled with a rather nasty irritating venom. Having been shaped by aeons of natural selection, they perform their defensive duties quite well. The bristles penetrate the flesh of any fish that tries to bite the worm. They fracture in the wound releasing the venom into the predator's tissues, and the bristles hold them in the wound increasing the irritation factor. The poison is not designed to kill anything, but it is designed to severely irritate the fish. As many fish can learn to avoid unpleasant stimuli, the bristles function to deter the predator. The bristles are eventually absorbed by the predator (or the aquarist) over a period of a couple of days, with no lasting harm, but leaving the potential predator with a real strong desire not to do that again. Most reef fishes are quite long-lived after they have reached maturity, and a deterrent is far more effective than a lethal toxin in such a situation. The fishes may learn not to attack the worms (although this will vary from fish to fish; my mature Premnas female either is a masochist or has intelligence measured in negative numbers as she continues to persist in attacking the worms) and such learning is likely good for years. Learned deterrents, such as this, result in fewer attacks and reduced damage to the worm than if the fish were killed and the whole attack process had to be repeated frequently.

In contrast to the other large beneficial fireworms found in our tanks, one species decidedly presents problems for a reef aquarium. This species, Hermodice carunculata, is a fireworm species commonly found in the Caribbean, although other species in the same genus are found throughout the tropics. It is the only potential "problem" fireworm in aquaria because it eats stony corals and gorgonians in its natural habitat, but may also prey on Indo-Pacific soft corals in the aquarium. As with all fireworms, this species has no jaws to bite off chunks of food, rather it must lick them to death. As the worm lacks the jaws to sever the pieces of its prey, feeding in Hermodice is a prolonged process. When they feed, Hermodice individuals typically swallow the ends of a gorgonian or soft coral and then proceed to lick the flesh off of it, while the ends are still attached to the colony. Such feeding is a lengthy process; it takes hours. During this period the worm really isn't going to go anywhere, it is tethered to its dinner. This species is also an obligate predator of these prey, although it may scavenge a bit, it will not, - in fact, it cannot, - eat other prey. If you have a Hermodice in your tank, you will either eventually find it on a prey organism munching away or see it crawling across the substrate. Remove it with a pair of forceps, tweezers, or tongs, and dispose of it.

Figure 3. A predator to avoid; the worm illustrated here is Hermodice carunculata, the large predatory fireworm commonly found in the Caribbean. It is very rarely found in reef aquaria. A. A scanning electron micrograph of the front end of a Hermodice individual; (M= the mouth, P= the parapodia, and C= fringe-like tentacles found on the caruncle). Note that that fringe is evident as bright red patch in the other images; also compare with Figure 1, and see that the fringe is absent on Eurythoe. If all else fails, if the worm has a bright red spot on the top of the head, it is likely a Hermodice. B. A large Hermodice individual approaching a dead crab or crab molt. Even predators sometimes scavenge. C. An individual eating the tissue off a gorgonian branch; it has swallowed the end of a gorgonian branch and will rasp the tissue off it. Images in B and C are courtesy of James Wiseman.

All other fireworms in our tanks are content to gum food or dead animals. They do not perceive of live animals as prey, and in particular, they will not eat or enter Tridacna as susupected commonly by aquarists. In nature, as well as in some reef aquaria, fireworms will aggregate under these large clams. It simply is a good haven for them. If the clam dies, they may gnaw on the corpse, but they won't attack and kill it. In fact, as they determine their prey by odor, they won't even perceive of any healthy animal as a food source, nor will they attack it.

Other Big Worms

Only two other groups of polychaetes, the Family Eunicidae, and the Family Lysaretidae contain large worms that are commonly found in reef aquaria. The first of these groups, the eunicid worms, is a large diverse group with over 200 species. The second, the lysaretid worms, is a small group with only about ten or fifteen described species; unfortunately, the lysaretid worms are predatory and deadly to many reef aquarium inhabitants. Even more unfortunately, they are reasonably common in live rock.

How To Max Out Your Worm Quotient

Eunicid worms are formidably complex animals. They are described as having an eversible pharynx, meaning they have an extensible tube that projects outward from the mouth. This tube is armed with two to five pairs of large forceps or pincher-type lateral jaws and one pair of additional jaws that are ventrally situated. This group contains the largest polychaete worms. There are some reliable reports of eunicid worms being an inch in diameter and fifty feet long, although the largest confirmed specimens are smaller. Specimens in excess of six feet long are common in nature, and occasionally such giants are found in marine aquaria. They are also long-lived. I have had one for several years now; transferring it from tank to tank during remodels and revisions of my system.

The eunicid worms found in aquaria all have five antennae, with a large pronounced antennae arising from the center of the "forehead." Large eunicid worms from two distinct groups are found in aquaria. Both enter the tanks hidden in live rock. The most distinctive of these are worms in the genus Palola. These are rock-inhabiting worms that reach lengths of three to six feet. They are generally dark green to blue to black and are largely nocturnal. They will extend from rocks to feed and appear to be mostly scavengers or detritivores. However, little is known about their diets in nature, and if any are found in aquaria, they may well be able to eat small fish or shrimp. On the other hand, there is no hard data that they do so. Palola is a genus whose synchronous spawning is legendary. Prior to such spawning events, the rear portions of the animals are filled with eggs and sperm and, when the time is right, they spawn. The spawning cues appear to be lunar and tidally influenced, but whatever the trigger, most of the worms in large geographical areas spawn within a few minutes. The rear portion of the worm separates from the front portion and swims to the surface where it writhes around and ruptures. With millions of worms spawning at once, the sea literally becomes covered in a wriggling mass of large worm fragments. It is thought that mass spawnings of this nature occur because although predators will be attracted to such spawns to eat the worms and their gametes, there will be so many animals spawning that the predators get sated, and many of the eggs escape to become fertilized, and undergo development into juveniles. Palola worms are probably harmless in most reef tanks, but if one does spawn, it may produce enough gametes to seriously foul the tank. They are often found dead or dying in uncured live rock.

Worms in the genus Eunice, sometimes called "bobbit" worms are, if anything, more impressive than their Palola cousins. Eunice is a large genus, with well over 150 species, and it is hard to generalize about them. As with the Palola, they have five antennae, including one in the center of the forehead and they all have jaws, in some cases wicked, scimitar shaped hooks with accessory spines and hooks. These are not jaws for chewing the prey or food item, but rather are jaws designed to ensure the food that, once seized, never gets away. Some of these worms get very large; the largest I have seen reported from reef tanks was in excess of 6 feet long, and individuals of Eunice aphroditois may be much larger. Eunice individuals tend to live in mucus-lined borrows in rock or sediments and may have several entrances to their tubes. Two distinct kinds of worms seem to be represented in this genus. One kind, which is benign in reef tanks, seems to be mostly scavenging its food. It lives in a burrow in the sediment, or more rarely, in a burrow in the rocks. When feeding, one of these worms will slowly extend from its burrow. They typically have four to six eyes and are quite capable of detecting motion outside the aquarium, and across the room. It will slowly search the surrounding area for food and if bothered by a fish, or its own shadow, will retract into its burrow with a velocity that has to be seen to be believed. Contraction back into a burrow has been clocked in excess of 20 feet per second, and if only a couple of feet of the worm are visible while it is foraging, that worm can disappear, quite literally, in the blink of an eye.

Figure 4. This is "Max," the large Eunice individual that I have had in my aquaria for about five years. A. The head, note the characteristic five head tentacles from the head, and specifically note the one arising directly from the center of the "fore head." The worm is about half an inch across. Note the complete lack of visible setae or bristles; eunicids do not have the white protective bristles found in fireworms, and they often keep their other bristles withdrawn. B. In August of 2002, I had to move Max from one tank to another, and he broke into three fragments. His total length was over four feet long. He has recovered from this and is living in my present tank. He is shorter, but I anticipate he will grow to his former length. C. Note the gills and compare them to the ones on Eurythoe in Figure 1.

All of the large Eunice individuals that I have heard about in reef aquaria seem to be scavengers. However, the largest Eunice individuals seen in nature are impressive predators. Individuals have been reported to strike upward from the sediment surface, grab a four-inch long fish swimming above the sediment, pull it under the sediment and presumably snack on it at its leisure. Such worms are also reported to be an inch in diameter and about thirty to fifty feet long, making them a bit larger than most home aquaria could accommodate.

There are also smaller species of Eunice, and these seem to be reported from time to time in aquaria. They generally appear to be harmless scavengers, however, even I, a self-proclaimed vermophile, would consider them amongst the "usual suspects" if some small fish such as fire fish or small gobies disappeared without a trace.

Regardless of the size of its individuals, the major characters for identification for the identification of eunicid species would be the absence of white tufts of setae, and the presence of five large and visible antennae (large relative to the worm, not the aquarist), such antennae are typically about two to three body diameters in length. Colors are secondary characters with these animals, but the Palola worms are often dark colors, while the Eunice individuals are, typically, shades of brown.

The only other large worm likely to be found in aquaria is the lysaretid polychaete Oenone fulgida. These animals are related the Eunicids, and, like them, possess jaws. They have three small antennae tucked in the groove between the two segments that make up the head, and a single dark eyespot may be visible on either side of the head.. Oenone fulgida has been reported to be circumtropical, and is quite variable for a single species. These studies date from the 1920s and it is quite likely that modern research, supplemented with genetic analyses, would show that what was thought to be one species eighty years ago is really several different species. The poorly studied nature of Oenone works against us, unfortunately, as it is relatively common in aquaria.

Whatever its status, animals that we presently refer to as Oenone fulgida may be easily recognized. As with the rest of the eunicid group, these worms lack the white tufts of setae characteristic of the fireworms. In fact these lysaretids tend to look relatively smooth, often without obvious appendages on their sides. This is an illusion, however, as they do have good appendages off of each side of each segment. The three antennae on the top of the head are small and often not visible, so the head looks smooth. In this particular case, color is a reasonably good characteristic to use in identification. Oenone individuals are typically orange, ranging from a dull, purplish orange to a brilliant blaze orange. They may be large worms, fully-grown adults often extend out of their burrows for two feet or more, and when fully extended they may be one quarter to one eighth of an inch in diameter. They typically live in burrows in rocks, but also may be found in tufts of algae or inside the water channels of large sponges. They are quite adept at detecting movement and will rapidly withdraw into their burrow if they are startled. Their withdrawal response, however, is not as rapid as that of Eunice individuals.

Oenone are nocturnal predators on snails and clams, and perhaps some other animals. They appear to extend from their burrow, and as they approach their prey they apparently secrete some mucus that covers the prey. This mucus may simply smother the prey, or it may contain some venom or narcotizing agent. After the prey is immobilized the worm extends a proboscis from the bottom of the head into the mucus and the jaws grasp the body of the prey. The jaws may also cut the attachments of the body to any shells, or alternatively the mucus may contain an agent that chemically severs the attachment. In any case, the prey's body is ingested. When the aquarist investigates the scene the next morning, all that typically remains is an empty snail or clam shell covered in a blob of mucus. Not many other predatory animals in marine aquaria typically leave behind such remains, consequently a dead, empty, shell covered with mucus is considered to be good evidence of the presence of an Oenone.

Figure 5 . This is the front end of a small individual of Oenone fulgida. Note the basic orange cast to the worm. This worm was about four inches long and about a quarter inch wide. A. Note the round "snout," or prostomium, and the three small tentacles at the top of the head. This configuration of snout and tentacles differs from the Eunice species (see Figure 4) and the fireworms (see Figures 1-3) and it is visible with a magnifying glass or hand lens. Note the relatively narrow segments as well; these make the worm appear smooth and lacking segments when viewed from a distance of about eight or ten inches. B. This is a lateral view of the head and front end of a preserved specimen. Note the proboscis is protruded from the mouth. These worms use the jaws located in the proboscis to grasp and manipulate food. C. This is a view of the head from directly above, showing the characteristic three tentacles. There is a single dark eye normally visible on each side of the head, but the eye pigments have faded in the preservative.

Oenone fulgida are not too hard to remove from a system, but it takes diligence. They most often live in burrows in rock, and enter aquaria in uncured rocks, and being nocturnal, the hobbyist has to search for them in the middle of the night. Using a red flashlight is best, as they will rapidly withdraw in the beam of a normal flashlight. They will appear as long worms stretched out and over the rocks. Once an Oenone individual is presumed to be living in a tank, the hobbyist must watch it withdraw in order to see where its burrow is found. After the rock with the burrow is located, the rock must be removed and the animal flushed from its burrow using a flood of carbonated water (soda pop works well). The worm is then discarded, and the rock replaced in the aquarium.

Few other large worms are found in aquaria, although they may be quite common on reefs. I have occasionally seen reports of two other types of large worms found in aquaria. These are scale worms, and phyllodocid worms. Although unrelated, these worms have some similarities of appearance. The small appendages off of either side of a segmented worm's body are called parapodia, and these often have several fleshy lobes. In the scale worms, the uppermost of these lobes may have a secondary lobe on it that grows quite large and lies on the upper surface of the animal. These large lobes look like large fish scales, and give the worm their common name. There are quite a large number of scale worm species, and they belong to several different, but apparently related, groups of species. The distinctions between them seem to be manifested in the amount of the upper part of the worm covered by the scales and by the pattern of the scale arrangement. Scale worms are generally quite small and rather "compact" worms, but some species reach lengths of about a foot or more, and a few of these larger individuals have been sighted in aquaria. Scale worms are often found as commensals or symbionts on echinoderms. Other species seem to be mostly predatory. None of them seem to persist in aquaria, probably because their preferred and necessary foods are absent from the aquarium systems.

Figure 6 . Scale worms. A. A small free-living scale worm about an inch long. Note the scales covering the upper surface. One scale is found between ends of the yellow lines. Scale worms often appear flattened. B. A commensal scale worm found living in and on a sea star. The worm's back end is situated in the sea star's mouth. The scales are quite evident covering the dorsal surface. This worm is reported to attack any predators attacking its sea star, and it has sufficiently large jaws to, on occasion, drive off the predators.

Phyllodocid worms are also predatory, but unlike scale worms they are typically long and slender worms. The upper lobes on their parapodia are enlarged and shaped like a large simple plant leaf. These parapodial lobes generally do not extend over the worm's body, but overlap the parapodia behind it. In addition to these large parapodial lobes, the heads of these worms are quite distinctive. They typically have one or two pairs of large and evident eyes. Unlike the eunicids, phyllodocids do not often show a flight response and one often sees them out hunting in daylight. It is possible that they have a noxious taste or some other predator defense, but that has not been tested. Elsewhere on the head are several pairs of long tentacles extending forward of the worm and out laterally on each side of the head. Phyllodocids lack the "forehead" tentacle characteristic of the eunicids. They are active predators, often on other worms, and hunt down, attack and kill their prey. They have been seen infrequently in reef aquaria, but reports of their presence seem to be increasing. Some species reach lengths of a couple of feet, but most are a few inches long. As with the scale worms, they don't seem to persist in reef aquaria, presumably as such aquaria cannot support the diversity of prey necessary to maintain them.

Figure 7. Phyllodocid worms are predators; these worms were photographed while "out on the prowl." A. This worm was about five inches long, but was only about a sixteenth of an inch across. The enlarged dorsal parapodial lobes look like flaps along the side of the animals and are the identification characteristic of the animals. B. Another, smaller, phyllodocid worm. This animal was about one thirty second of an inch across, but it was still about four inches long. Note the foraminiferan for a size scale. The large eyes and extended sensory tentacles characteristic of these predators are also evident in these images.

Large polychaete worms, as with large animals of any taxonomic persuasion, require lots of food and large amounts of suitable habitat space. It is interesting that reef aquarists have inadvertently built such habitats in their tanks. The fireworms, in particular, seem quite pre-adapted for reef aquarium existence, and their populations in reef aquaria are thriving. The number of these worms in such systems is quite large, and for the fireworms in particular, their numbers probably dwarf those of all other species the same size or larger in reef aquaria. We might, with a great degree of accuracy, refer to our tanks not as coral reef aquaria, but rather as tropical reef worm habitats. The success aquarists have keeping other animals is to a great extent dependent upon their success at keeping thriving populations of these scavenging worms.

Next month, I will conclude this series on the segmented worms of reef aquaria by discussing the smaller species that occupy the sediments of our systems.

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

For Everything You Wanted To Know About Worms But Were Afraid To Ask:


Useful or Cited References:

Fauchald, K. 1977. The polychaete worms; definitions and keys to the orders, families, and genera. Science Series 28. Natural History Museum of Los Angeles County. Los Angeles, CA. 188 pp.

Fauchald, K. and P. Jumars. 1979. The diet of worms: a study of polychaete feeding guilds. Oceanography and Marine Biology Annual Review. 17:193-284.

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Polychaete Annelid Identification, or “You Can Always Tell A Bristle Worm… by Ronald L. Shimek, Ph.D. - Reefkeeping.com