VARIETY OF CLAM ARTICLES - A variety of article authored by Daniel Knop.
A Brief Guide to the Selection and Placement of Tridacnid Clams - "
Do you
want to dress up your reef tank by adding a Tridacnid clam? If you're like many
reef hobbyists, the answer is a resounding "Yes!"
Identifying the Tridacnid Clams - " It is the shell of each specimen which is typically the key to identification,
not just the flesh. "
Clams - "
Tridacnids, however, are very unusual clams; they have symbiotic zooxanthellae
and they also have an internal anatomy that is oddly oriented relative to their
shells. "
Clam Data Base - Species specific information, a very good presentation.
The Flame Scallops - "A detailed article about the care of these mobile bivalves. "
When placing your new clam or having to move one already
in the tank, I have found that for the majority of species, they do
better when placed up into the rock landscaping, which is usualy a hard
thing to accomplish since the clams have a habit of slamming their
shells shut and tipping themselves over or having something else, such
as a snail, push them over and out of the rocks. Since clams can and do
excrete anchoring filaments when given the time to do so, usually a
matter of a day or two at most, I will use super glue gel to glue one
side of the shell to a rock holding the clam in place long enough for
it to anchor itself. Keep in mind, only glue one half of the shell to
the rock(s) leaving the other half with enough room between any rocks
for the clam to able to open. Do not glue to bottom of the clam as this
is where it is open and excretes its anchoring filaments.
For those with sufficient light intensity (metal halides),
placing the clams on the sandbed seems to do them no long term harm
that I am aware of. Although I have never seen a clam in the wild that
was sticking up out of the sand and are always found in amongst the
rocks and corals, its shell being embedded down into the rock/coral
substrate affording the clam protection from below and its sides.
Circulatory
- The heart of a clam lies just below the hump of the shell within the
pericardial cavity, the only remains of the coelom. Therefore, the
coelom of the clam is said to reduce. The heart pumps blue blood,
containing the pigment hemocyanin instead of red hemoglobin, into
vessels that lead to the various organs of the body. Within the organs,
however, blood flows through spaces, or sinuses, rather than through
vessels. Such a circulatory system is called an open circulatory system
because the blood is not contained within blood vessels all the time.
This type of circulatory system can be associated only with an inactive
animal because it is an inefficient means of transporting oxygen and
nutrients throughout the body.
Digestive -
The clam is a filter feeder. Food particles and water enter the mantle
cavity by way of the incurrent siphon, a posterior opening between the
two valves. Mucous secretions cause smaller particles to adhere to the
gills, and cilia action sweeps them toward the mouth. The digestive
system includes a mouth, a stomach, and an intestine, which coils about
in the visceral mass and then goes right through the heart before
ending in an anus. The anus empties at an excurrent siphon, which lies
just above the incurrent siphon.
Exocrine -
There is an accessory organ of digestion called a digestive gland. The
digestive gland surrounds the stomach and is composed of numerous
tubules, which are formed at the distal ends of branching ciliated
ducts. Nutrients from the stomach enter the tubules through these
ciliated ducts and are absorbed by the glandular cells lining the
tubules and digested intracellularly. The crystalline style (stalk)
extends from the style sac into the stomach. The style contains
amylase, which helps digest the starches present in the food. Thus, the
digestive gland is both secretory and absorptive. In addition, the
style usually (in other bivalves) harbours many spirochete bacteria
that are thought to secrete additional digestive enzymes. Wastes from
the digestive gland tubules are returned to the stomach and are
eventually swept into the intestine.
Excretory -
There are two excretory kidneys in the clam, which lie just below the
heart and remove waste from the pericardial cavity for excretion into
the mantle cavity. The clam excretes ammonia, a poisonous substance
that requires the concomitant excretion of water, Land-dwelling animals
tend to excrete a less toxic substance in a more concentrated form.
Immune - Internal
defence in bivalve molluscs, like all invertebrate species, is based on
an innate, non-lymphoid immune system which consists of a variety of
cell types and effector molecules interacting to maintain efficient
elimination of foreign bodies. Phagocytic blood cells (cell that
removes unwanted substances) or haemocytes, are the principal effector
cell for immune defence. The phagocytic response of the haemocytes is
complemented by an array of killing mechanisms which may include,
release of degradative enzymes and the generation of reactive oxygen
metabolites. Antioxidant enzymes may also be present to minimise the
potential damage for adjacent tissues and cells from these reactive
oxygen metabolites. Haemocytes may also release other soluble compounds
as part of their defence strategies. Recent research has identified the
composition of a number of antibacterial peptides in bivalve molluscs.
Musculo-skeletal
- In a clam, the shell is secreted by the mantle and is composed of
calcium carbonate with an inner layer of mother-of-pearl. If a foreign
body is placed between the mantle and the shell, pearls form as
concentric layers of shell are deposited about the particle. The
adductor muscles are used to open and close the shells.
Nervous and Sensory - The clam nervous system is composed of three pairs of ganglia, which all are connected
by nerves. Clam lack cephalization. The foot projects anteriorly from the shell,
and by expanding the tip of the foot and pulling the body after it, the clam
moves forward.
Reproductive -
The male or female gonad of a clam can be found about the coils of the
intestine. Reproduction takes place when male and female clams release
sperm and eggs into the water. Fertilized eggs develop into
free-swimming larvae before settling to the bottom. While all clams
have some type of larval stage, only marine clams have a trochohore
larva.
Respiratory
- Within the mantle cavity, the gills hang down on either side of the
visceral mass, which lies above the foot. Gills are composed of
vascularized, highly convoluted, thin-walled tissue specialized for gas
exchange.
Clams as filtration ?
- Having seen this being promoted and asked about, I
thought it a good idea to address such a "method". If by chance
you read the above anatomy descriptions you would have noted that clams
are filter feeders, of plankton. Which can only produce the same waste
materials, most notably, ammonia, that any animal that eats would
produce. I fail to see how loading an aquarium system with clams could
ever have an effect on nitrate production as being suggested by others.
Quite the opposite would happen. That and being plankton filter
feeders, I would see them as a big competition for food that other tank
inhabitants could and would utilize, such as my corals and other
invertebrates.
Having a reef system, and trying to provide
for the animals food requirments is hard enough without having a number
of clams being in direct competition for the same resources. Any area,
such as a sump or refugium compartment would much better serve a reef
aquarium if used to promote the production of plankton, not its
removal.
For nitrate reduction, its not going to
happen through the use of clams. For water clarity, sure, if you want
to deny your corals the chance at what little plankton our systems can
produce. All around, I feel this is just an idea that has not
been thought out through to its biological conclussions. As happens
quite frequently within this hobby.
