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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.
So...
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.
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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.
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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.
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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.
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Here are some links to terebellid information
including some diagrams of the worms.
www.arl.nus.edu.sg
www.nhm.ac.uk
www.museum.vic.gov.au
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.
depts.washington.edu
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:
www.arl.nus.edu.sg
www.nhm.ac.uk
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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.
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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.
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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.
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Here are some links to aquarist pages where
cirratulids are mistakenly called "spaghetti worms"
or terebellids.
www.geocities.com/Heartland/Garden/
home.att.net/~willowmarine/pictures/spaghetti_worm
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...
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