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Reefkeeper's Guide to Invertebrate Zoology Aquarium Net November 1997

Reefkeeper's Guide to Invertebrate Zoology:

Part 10: Sedentary Polychaetes, Con't.

Well, just in case you missed the last article, I'd better give some sort of introduction here before just leaping into a shopping-list of polychaete family descriptions. In part 9, I completed my introduction to the dreaded "bristleworms" (used here as a loose synonym for polychaete) and began to describe the first five families of the "sedentary" (generally loosely interpreted as tube-dwelling) polychaetes (Chaetopteridae, Cirratulidae, Pectinariidae, Sabellariidae, and Sabellidae). I tried to emphasize that despite their bad reputation, none of these worms are likely to cause damage in a healthy reef tank, and that, indeed, many of them are both useful and attractive additions to a well-balanced reef tank. This month I'll finish up my discussion of the sedentary polychaetes (Serpulidae, Spionidae, Spirorbidae and Terrebellidae). I'll then go on to discuss a little bit about the other functional classification of polychaete worms, the Errantia. The next article will then describe the families of "errant" (generally interpreted as free-living) polychaetes in much the same manner as these two have described the sedentary polychaetes.

Serpulidae (sir-pu-lid-day)

The christmas tree worm, Spirobranchus giganteus . The serpulids are a family of calcareous tube-dwelling worms that, like the sabellids (check the last article for that description), often have magnificent tentacular crowns, and are generally sought after by many aquarists. One of the most attractive (and best known) examples of this family is the "christmas tree" worms ( Spirobranchus giganteus , pictured here).

As I mentioned in the last article, a good rule of thumb to differentiate the sabellids from the serpulids is the presence of a hard calcareous tube. However, as I also mentioned, this rule-of-thumb is not always useful because some sabellids produce calcareous tubes, and some serpulids have soft, leathery tubes. An additional character to help decide wether that tubeworm in your aquarium is a sabellid or a serpulid is the presence of an operculum . The examples that I have used for these two families, Sabellastarte (for Sabellidae) and Spirobranchus (for Serpulidae) have very different tentacular crown structure, but other serpulids, such as Hydroides dianthus (pictured here) have a crown very similar to that of Sabellastarte (the Hawaiian featherduster worm), but the obvious operculum (noted by the arrow) indicates that this animal is definitely a serpulid polychaete.

Spionidae (sp-on-id-day)

Spionids are a family of small, thin polychaete worms that either burrow, or form delicate tubes composed of sand or mud (e.g., Polydora, Spio, Streblospio). The easiest feature with which to identify a spionid polychaete is the presence of two long, coiled peristomial palps (feeding "tentacles" originating from the "head") which are grooved. Most species use these grooved palps to selectively scavenge detritus and tiny organic particulates from the surfaces around their tube. Although not quite as versatile with their "tentacles" as their cousins, the Terebellids, they feed in a very similar manner (discussed in Terbellidae, below). You will most likely not see the worm, but instead see only the two tiny, hair-like palps swinging back and forth in the water flow searching for food particles.

An unidentified spionid polychaete from the California coast These worms are uniformly small (rarely exceeding 2 mm in diameter, about equal to a pencil lead, or a few cm in length), and if you see a couple of palps waving about from a worm that is quite thin, but a couple of inches in length it is most likely Phyllochaetopterus or Mesochaetopterus (see Chaetopteridae, at the beginning of last month's article) rather than a spionid polychaete. In any case, neither group is likely to be harmful to your reef aquarium, so there is no need to attempt to remove them.

Having said this, however, there are some spionids that burrow into any calcareous substrata, including the shells of molluscs, to make a safe home. Even these species are not dangerous to most large molluscs in small numbers, but if they become plentiful enough, they can weaken the shell to the extent that it easily breaks. If you notice many small pairs of palps protruding from holes in the shell of your prize Tridacna, you may want to kill the worms by heating a large sewing needle, and inserting it gently into the hole (MAKE SURE you don't go through the shell and touch the clam!! You only want to kill the worm!). Many worms form their tubes on or in between structures of other animals, so don't panic if you see palps extending from the side of an animal. If the worms are not plentiful, or are not actually embedded IN the shell of the animal, you can (and should) ignore them as harmless scavengers. It is only when a calcareous burrowing species reaches high density that members of this family can cause problems.

Spirorbidae (spear-ror-bid-day)

I think spirorbids are the worm about which I field the most questions, because their tiny calcareous tubes are almost ubiquitous among reef aquaria, and they are so small that unless one looks carefully, you cannot see the crown worm itself, just the circular spiral of the calcareous tube (as pictured here). I usually receive questions to the effect of, "There are tiny calcareous spirals all over the glass and rocks in my tank. Are they egg masses of snails or something?" If you take any hand lens and look carefully at those spirals, you will most likely see a tiny set of pinnules and a tiny operculum which both resemble the structure shown in the photo of the serpulid tubeworm, Hydroides dianthus , above. Although this species, Spirorbis borealis , is restricted to cold water habitats, all spirorbids look very similar to the casual observer. The primary difference you may notice is wether the shell coils to the right or to the left.** Like the sabellids and serpulids above, these worms have two distinct body regions: a tentacular crown which projects from the tube for feeding and respiration, and a soft, fleshy body which remains permanently within the safety of the tube. The tightly-coiled, calcareous tubes attach permanently to any available hard substrata, and the anterior end of the tube is sealed by an operculum similar to that of the serpulids when the worm withdraws into its tube. Serpulids, however, do not grow in the characteristic coiling pattern of the spirorbids (which may coil to the right or left -- sinistral or dextral -- depending on the species) which is unique to the spirorbids. Once again, these worms are virtually harmless. These animals brood their larvae in either the operculum itself, or within the tube until ready to metamorphose, and then release very short-lived planktonic larvae. These larvae often settle within minutes (and almost always less than an hour) of their release, and can therefore spread rapidly within a reef aquarium. This generally happens early in the life of the aquarium, and in a well-maintained, clean aquarium, the initial population explosion of these small worms quickly slows and they are almost never a problem in any aquarium. If the population continues to climb to the point that all surfaces in the tank become encrusted with these worms, it likely indicates a high suspended organic problem, and you should be more concerned with your water quality than the presence of these polychaetes, per se .

Terebellidae (tear-i-bell-id-day)

The final group which I would like to discuss in this article are the terebellids, more commonly known by the common names "spaghetti," "medusa" or "mason" worms. These worms are extremely common in shipments of both live rock and live sand, and are usually one of the first worms to raise questions among aquarists new to reef keeping. They can live in holes within live rock, buried in the sand, or in temporary tubesmade from debris they collect, which they generally attach to the bottom of any hard surface they encounter (such as rocks, corals, large clams, etc.).

Once again, these worms have two distinct body regions: a soft, fleshy body, and a head which is almost invisble due to the large number of long, spaghetti-like (hence the name) feeding tentacles. Also extending from the head are many, often brightly, highly branched branchiae (gill-like appendages) which function in respiration. Because these worms spend most of their lives partially or completely buried in the sediment they require the branchiae to ensure sufficient gas exchange to maintain the activity of their widely roaming tentacles. These worms are selective deposit feeders, and as such pose no real threat to your aquarium. As with the families listed above, if these animals become so abundant as to cause concern, your concern should be with your general aquarium conditions rather than the presence of the worms themselves.

Errant Polychaetes.

Unlike the sedentary polychaetes, of which few are any threat to a healthy reef tank, some errant polychaetes can be a substantial threat both to your tank and to you as well. Most hobbyists to whom I speak generally assume that nothing that is legal to sell in a pet shop can harm them, but I have seen (and purchased) highly venomous animals that are capable of hospitalizing the unfortunate soul who would grab them in several different pet shops. Just because the item is for sale does not mean that it is safe. Among those animals are Hermodice carrunculata , one of the infamous "fire worms" that have been instrumental in giving "bristleworms" their bad reputation. I think much of this confusion has developed from the sloppy use of common names among reef keepers and retailers. Bristleworm has traditionally been applied generically to any polychaete ("many bristled") worm, but at some point in the hobby (way back when I was actively involved in retail), the term "bristleworm" became synonymous with "fire worm" and people were told to watch out for them in their aquarium. As hobbyists have become more sophisticated, and more species have become generally available, the terminology is slowly switching back to a generic class designation, but throughout this transition there has been a lot of confusion and unnecessary panic over harmless (and unavoidable) polychaete populations in home aquaria.

Source Literature:

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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