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Aquarium.Net Oct 96 Segmented and Vermiform

In this article Ron Shimek covers various worms found in both fresh and marine aquariums. Oct. 1996 Index for Aquarium Net, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Segmented and Vermiform, it's a way of life..

By Ronald L. Shimek

Some of the most beautiful, and most cursed at, occupants of reef and other aquaria are worms. Additionally, worms can be both incidental and chosen inhabitants of fresh-water aquaria. There are a LOT of different kinds of worms; virtually every animal group has animals that could be called worms and some animal groups are composed wholly of worms. So, what is it about being long, slender, and basically cylindrical that makes it such a successful way to be an animal.

Well, probably the best explanation is that wormy animals can get into small holes or burrow through unconsolidated, sandy or muddy, substrates. These types of habitats offer protection against some predators such as fishes, and often contain many different kinds of food that can be exploited.

Most of the visible worm-like animals in aquaria belong in the Phylum Annelida, the segmented worms. There are an estimated 10,000 to 15,000 species of animals in this phylum, although this is almost certainly a gross understatement of their diversity ( Fauchald 1977 ). Recently many researchers have investigated the genetic material in some common worms and found that what had been thought to be one worm species was, in fact, several species that had exceptionally similar appearances ( Grassle and Grassle, 1974, 1976 ).

Suggested links for information on annelids (It was hard to narrow this list, a quickie net search on "annelids" gave 582 matches... These links will give a lot of information on the specific groups that are also indicated further below):

http://www.keil.ukans.edu/~worms/annelid.html

http://www.ucmp.berkeley.edu/annelida/annelidasy.html

http://phylogeny.arizona.edu/tree/eucaryotes/animals/annelida/annelida.html

Additionally, worms can be exceptionally abundant in marine ecosystems, particularly those containing muddy or sandy substrata. Abundances of 20,000 animals per square meter are common, and extreme abundances of 500,000 animals per square meter are occasionally noted ( Wilson 1990 ). Given these abundances and their diversity, it is has long been recognized that they are exceptionally ecologically important (see Snelgrove and Butman 1994; Rhoads, 1974; Rhoads and Young 1970, and Wilson 1990 for additional information). In fresh-water ecosystems, worms are not generally as abundant as in the marine ecosystems unless there is a LOT of organic material present. This kind of situation often develops near sewage outfalls, and in these areas, small worms, often in the genus Tubifex , can reach densities of millions per square meter (Pennak, 1992). These worms live buried head down in the muck, and wave their posterior ends up in the water to aid in respiration. According to the those who have been crazy enough to dive into these grossly polluted areas, the bottom often looks like thick moving velvet from all the worm butts wiggling back and forth.

Given this apparent abundance and importance in the real world, it is not surprising that these worms also are often abundant and diverse in many marine reef and some fresh-water aquaria. The worms that are present in aquarium systems are added by the aquarist either intentionally or accidentally. Most are added accidentally. Many of these worms have amazing powers of both sexual and asexual reproduction, however, sexual reproduction generally involves a larval stage that does not survive well in aquarium situations. Asexual reproduction, however, works very well.

There are numerous ways in which these animals can reproduce asexually. Often a worm can bud off new worms at various places along its body. Sometimes the adults will split into two or more daughter worms. Occasionally the animal will simply fragment, and the resulting fragments each will have the potential to grow into an new worm. It is worth remembering here that these are decidedly not simple animals. Their organ systems rival in complexity those of vertebrates of the same size, and in fact, the worms may be significantly more complex. Just as an example, the common feather-duster worms of reef aquaria have a closed circulatory system with arteries, veins, and capillaries, blood that contains hemoglobin, and SEVERAL PAIRS of hearts. Asexual reproduction by fragmentation in such animals is obviously not a simple event. However, it has been poorly studied, and the genetic controls and physiological events occurring during it are largely unknown. This is probably to the detriment of aquarists, a few of the pest worms of aquaria, such as "bristle worms", Hermodice carunculata , reproduce asexually very well. If we knew physiologically how this occurred, we might be able to easily control the populations of these worms.

Intentionally Added Worms - Marine Aquaria

Generally, in marine aquaria the intentionally added worms are in one of two closely related groups. Both are in the Class Polychaeta which contains most of the segmented marine worms. These are the feather-duster worms in the Family Sabellidae, and the calcareous-tube feather dusters in the Family Serpulidae. Both of these are tube-dwelling worms, but unlike many polychaetes which live in temporary tubes or tubes that they can leave, feather dusters are in their tubes for life. These two worm families are considered by the experts to be closely related, so there are many similarities of structure. They differ in minor anatomical characteristics, but probably few aquarists will want to dissect their expensive pets to find these.

Suggested link for more information on Polychaetes:

http://ucmp1.berkeley.edu/annelida.polych.html

In both groups the head has been highly modified to produce a crown of feeding tentacles - the feather duster. This is really a very complex structure of elongate rod-like tentacles with side branches; each of these tentacles does look like a small feather. The side branches of the feather, called pinnules, are the business end of the apparatus, where the food is captured. The tentacles are covered with microscopic beating hairs called cilia, and these both move the water past the tentacle crown and capture any food particles in it. The cilia knock microscopic particles, such as bacteria, particulate organic material, or small zooplankton toward the center of their pinnule into a groove that occurs there. This groove collects the food, and in an example of remarkable clarity for zoological nomenclature is referred to as the "food groove." The food groove is lined with gland cells that produce the mucus that covers the surface of the food groove.

Mucus is wonderful stuff! Chemically, a combination of sugars and proteins called a glycoprotein, under slightly acidic conditions mucus becomes very fluid, while under slightly alkaline conditions it is very viscous, but under most conditions it is sticky. The cells lining the food groove produce a slightly acidic secretion near their surface, so here the mucus is fluid and it flows moving under the influence of cilia. The top of the mucous stream, however, is in contact with the water column and is slightly alkaline, so it is stiffer and really sticky. In essence the animal has produced a conveyor belt of glue. Food particles that get knocked into the mucus stick to it and are moved downstream.

These animals are called ciliary-mucous suspension feeders as they use the cilia to capture particles and mucus to move them. The food groove from one pinnule meets and merges with the food groove in the center of the tentacle, eventually all of the food grooves dump their contents into a larger food groove at the base of the tentacles, and this in turn runs directly into the mouth. Additionally, the food groove sorts the particles by size and density. In cross-section, the groove is shaped like a "V" with steps on the edges so that has a wide upper portion, a discretely narrower middle area, and center area that is narrower yet. Large particles are moved in the upper section, middle sized particles in the middle, and narrow particles in the bottom. Heavy or dense particles sink to the bottom as well.

The large particles are moved to the base or tip of the pinnule and discarded. The middle-sized particles are moved to the base of the tentacles where they are collected into small sacs, mixed with mucus and some other chemicals and are used in construction of the feather duster's tube. In calcareous-tube feather dusters, the middle sized particles are also discarded. Only the smallest particles are actually eaten.

The tubes of feather duster worms are either parchment-like in the sabellids or calcareous in the serpulids. Both tubes are manufactured by the lip-like pair of ridges just below the crown of tentacles. Christmas tree worms, which have elaborate helical crowns of tentacles, chemically bore into corals, but also produce a calcareous tube of their own.

Many feather dusters are capable of asexually reproducing by fragmentation or budding, and some species, particularly in the genus Sabella can form dense aggregations in reef tanks where they get enough food. The large feather dusters that are commonly added to reef tanks are Sabellastarte magnifica , and are magnificent indeed! Unfortunately, in many tanks they don't live too long. These are animals with a relatively highly metabolic rate, and they need a reasonable amount of food. Unless the tank is fed well there may not be sufficient food present for them to survive.

When stressed, Sabellastarte individuals tend to autotomize their crown of tentacles, or to put it another way, "they loose their head." The animal can regrow a new head end in a few weeks - and the head can regrow a new posterior end, if it can last without being eaten. Generally, this head loss appears to be a response in aquaria to insufficient food. If the animal has had sufficient food, the worm will have sufficient food reserves to replace the crown of tentacles with one as large as the one lost, if the food reserves were low the tentacle crown would be smaller. Generally after one or two repetitions of this series of events, where the worm is progressively down-sized, it dies.

All of these worms can reproduce sexually, but this seldom occurs in aquaria. In the Families Sabellidae and Serpulidae, the sexes are separate, and typically males spawn first releasing a sperm suspension into the water. If there are females nearby, the chemicals in the sperm suspension will cause the females to spawn. If fertilization occurs, the embryo develops into a swimming larva within a few days. This larva needs to feed, generally on unicellular green algae, or a mixed algal culture ( Strathmann 1987 ). If the larvae survive the rigors of an aquarium system, and avoid being filtered out or eaten, the appropriate food is seldom available so they will starve. Raising the larvae is not a technically difficult task, however, and after a few weeks of feeding the larvae settle to the bottom and change into little worms. If food is available they will grow fairly rapidly. Perhaps some reader of this column will try to spawn and raise the worms.

Intentionally Added Worms - Fresh-Water Aquaria

Some fresh-water aquaria can become excellent habitats for a few species of worms. These aquaria are those with undergravel filtration, particularly if the gravel layer is thick and not disturbed much. Also most well-planted aquaria or those aquaria that have soil for plants will have acceptable worm habitats. If the aquarist adds live Tubifex worms to their system to feed their fish, some worms will make to the bottom and if it is acceptable to them, they will live in it. Unlike marine systems, the common segmented worms in fresh water systems are in the Class Oligochaeta, which contains the common terrestrial earthworms. Really most fresh-water worms look like smaller, thinner versions of earthworms, and many live in much the same way. They burrow through the bottom and eat organic material.

Suggested links for more information on Oligochaetes:

http://www.oit.itd.umich.edu/bio/Annelida/Oligochaeta.html

http://rivers.oscs.montana.edu/dlg/aim/annelid/oligo.html

Unlike those worms added to marine systems, the fresh-water worms are generally not added for aesthetic reasons. The number of people who get really excited by the beauty of earthworms is probably blessedly small... Yet, these worms can actually become a beneficial addition to the tanks, behaving much as other scavengers. Of course, they will be eaten by any fish that can get to them, so generally the populations in fresh-water tanks is never very great.

In addition to Tubifex , aquarists will also occasionally feed larger fishes earthworms. Earthworms can live quite happily in a well aerated aquarium and can persist for some time in the gravel or bottom sediment. As with the tubificids, however, they are fair game for fish predation, which will generally limit their life span.

Unintentionally Added Worms - Marine Aquaria

Worms are unintentionally added to marine aquaria through the addition of live rock or live sand. Additionally, holes in the bottom of pieces of coral or other calcareous material often contain hitchhikers. Although many different types of worms can be added in this, only two or three different types generally become either large enough or common enough to be noticeable.

Probably the most common of these unintentional worms are the so-called "bristle worms" or "fire-worms" of the Family Amphinomidae, and two genera, Hermodice and Eurythoe , often seem to make it into aquaria ( Shimek 1994 ). These worms are normally either carnivorous or carrion-feeders, and unfortunately the carnivorous species such as Hermodice carunculata browse cnidarians such as corals and gorgonians ( Vreeland and Lasker, 1989 ). Most of the bristle worms I have seen in aquaria are from the species Eurythoe complanata , which has been shown to mostly be a scavenger or carrion-feeder ( Fauchald and Jumars, 1979 ). Basically nocturnal, Eurythoe hides during the day and comes out to feed at night. Bristle worms get their common name from the conspicuous tufts of white, calcareous, hollow chaetae or bristles found along their sides. The hollow bristles are filled with a venom, which depending on the species of worm and the sensitivity of the victim can cause sensations in humans ranging from mild irritation to severe burning. These venom-filled bristles seem to be a very effective deterrent to predation, and few animals that are kept in aquaria eat the worms.

These worms can reach lengths of 50 cm or more, although the average size in most aquaria is much smaller. Their nocturnal behavior and their ability to hide in small holes or under objects allows many of them to go undetected. Often the populations in an aquarium can reach many hundreds or thousands, most of which are never seen. They seem to asexually reproduce rapidly and this property, coupled with their scavenging habits allows them to build up high population densities relatively rapidly. Although they have the potential for causing problems, generally small populations do no real harm in a reef system. Large individuals or dense aggregations can cause problems, however, and if possible they should be captured and eliminated.

Another type of worm that causes problems can be very large; I have seen individuals about 40 cm long and bright orange. These are thin compared to bristle worms, and although they do have small bristles along the sides, these are generally not apparent. These worms, Oenone fulgida , prey on snails and clams. They suffocate snails with a viscid mucus, and then eat the body, and apparently can bore into clams, such as Tridacna species and eat them as well ( Delbeek and Sprung 1994 ). They live in holes in rocks and emerge to feed, but generally keep their posterior end in their home hole. They are nocturnal and feed in total darkness. When startled by a light they can retract back into their den with extreme rapidity. About the only way they can be removed from a system is by removing their piece of rock and manually pulling the worm out if it possible.

Many other worms are often unintentional additions to marine tanks, but generally they are either benign or not particularly abundant, so their presence is not a problem.

Unintentionally Added Worms - Fresh-Water Aquaria

If the aquarist collects their own fresh-water plankton to feed their system or collects plants and animals from the wild some interesting unintentional worms can be added to their systems. The segmented worms that are often added from this source are in a third class, the Class Hirudinea, or the leeches. Leeches are particularly common in many fresh-water natural habitats and most of them can tolerate the conditions found in fresh-water aquaria quite well. Many leeches are strikingly attractive animals, with coloration patterns that can be very beautiful, for example, some common North American leeches are dark green with brilliant gold lines on them. Nonetheless, most of them are grey to black. While many leeches are predatory, mostly on small invertebrates such as snails or insects, a large number of species are specialized to suck vertebrate blood. All leeches really are bad news in an aquarium and should be removed and disposed of. If they are noticed feeding on a fish, they can be removed by netting the fish and placing it into a weak saline solution for a brief period. Alternatively, the aquarist can wait until the leech leaves its host, and then hunt for it in the tank.

Suggested links for more information on leeches:

http://www.oit.itd.umich.edu/bio/Annelida/Hirudinea.html

http://muse.bio.cornell.edu/!worms/taxonomy.html

When all things are considered, the segmented worms make interesting additions to our captive ecosystems. Generally they are beneficial or benign, with only a few species causing problems.

Comments or questions?

Illustrations:

Hermodice carunculata - A bristle worm eating the end of a gorgonian's branch. (and evidence of the underwater photographer's Murphy's law # 534, your strobe always quits just before you find the picture you want to take).

Hermodice carunculata - A common bristle worm.

Sabellastarte magnifica - Close up of tentacle crown of the magnificent feather duster worm from above. The structure of the feeding tentacles and captured food particles are visible in the food grooves of a few tentacles.

Sabella sp. - A typical feather duster worm, this forms "colonies" or clusters of worms by asexual reproduction.

Spirobranchus giganteus - The "Christmas Tree Worm", a calcareous tube dwelling feather duster worm that bores into coral. Both of the "trees" are parts of the same worm's crown of feeding tentacles.

Eurythoe complanata - A sand-dwelling bristle worm from a Caribbean coral reef.

References Cited :

Delbeek, J. C. and J. Sprung. 1994. The Reef Aquarium. Ricordea Publishing. Coconut Grove, FL. 544 pp.

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

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.

Grassle, J. P. and J. F. Grassle. 1974. Opportunistic life histories and genetic systems in marine benthic polychaetes. Journal of Marine Research 32: 253-284.

Grassle, J. P. and J. F. Grassle. 1976. Sibling species in the marine pollution indicator Capitella (Polychaeta). Science 192: 567-569.

Pennak, R. W. 1992. Freshwater invertebrates of the United States. 3rd edition. John Wiley and Sons. New York.

Rhoads, D. C. 1974. Organism-sediment relations on the muddy sea floor. Oceanography and Marine Biology: an Annual Review 12: 263-300.

Rhoads, D. C. and D. K. Young. 1970. The influence of deposit-feeding bottom sediment stability and community trophic structure. Journal of Marine Research 28: 150-178.

Shimek, R. L. 1994. Bristleworms. Aquarium Frontiers. 1 (2): 6-8.

Snelgrove, P. V. R. and C. A. Butman. 1994. Animal-Sediment Relationships Revisited: Cause versus Effect. Oceanography and Marine Biology: an Annual Review 32: 111-177.

Strathmann, M. F. 1987. Reproduction and development of marine invertebrates of the Northern Pacific coast. University of Washington Press. Seattle. 670 pp.

Vreeland, H. V. and H. R. Lasker. 1989. Selective feeding of the polychaete Hermodice carunculata Pallas on Caribbean gorgonians. Journal of Experimental Marine Biology and Ecology 129: 265-277.

Wilson, W. H. 1990. Competition and predation in marine soft-sediment communities. Annual Review of Ecology and Systematics 21: 221-241.

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