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| Bristleworms
are common on Chek Jawa. Most remain hidden or burrow into the
sand and mud. |
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'Polychaeta'
means 'many bristles'. There are about 8,000 species
of polychaete worms, making them the largest class of
the segmented worms.
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Bristleworms
are mostly less than 10cm long. Many are minute and live among the
sand grains.
Mobile versus immobile: Bristleworms
are often divided into those which are free-moving (called errant
polychaetes) and those which are not (called sedentary polychaetes)
which live in tubes or burrows. However, the distinction is not always
clear. There are errant polychaetes that live in tubes or don't move
about much and hide in burrows or other places. Other bristleworms
live in tubes.
Beautiful worms: Large, freely-moving
bristleworms can be attractive, with iridescent colours in shades
of red, pink and green. Among the most beautiful of bristleworms is
the fanworm with a delicate, patterned feathery
fan of feeding tentacles.
Wondrous worms: Bristleworms are
segmented worms, like the more familar earthworm. They are rather
more complex and well developed than they might seem. Their heads
bear eyes (from 2 to 4 pairs), sensory organs, the mouth and contain
a brain. Many have specialised feeding structures on their head. These
can range from powerful jaws to long tentacles that collect food.
Most have a well-developed blood circulatory system. Bristleworms
have amazing powers of regeneration. Many can replace body parts that
get chomped off by predators. This even includes the head!
Bristling worms: The rest of their
bodies are divided into similar, repeated segments. Each segment has
a pair of flattened extensions called parapodia. These appendages
are usually branched at the ends and covered with setae (bristles).
These bristly appendages are sometimes used to move (much like a millipede
does) and to burrow. In tubeworms, the appendages help grip the tube
walls and to move up and down the tubes. In some large, active bristleworms
which need more oxygen, the parapodia may also be modified into gills.
Don't play with fire! Some bristleworms
have setae made of calcium carbonate or silica which are brittle and
contain poisons. When the setae penetrate the skin, they break and
cause a burning sensation. These creatures are not surprisingly called
fireworms. Fireworms may release their bristles into the water too.
Don't touch bristleworms or the water that they are in!
Bristleworm food: Some bristleworms
are ferocious predators, hunting other worms and small animals. These
are captured with strong jaws that can be extended and retracted.
Some can inject a poison with their jaws. Some predatory bristleworms
live in tubes where they lie in wait for suitable prey.
Other bristleworms feed harmlessly on algae, others are scavengers.
Yet others feed on detritus. They may swallow sand and mud and process
these for the edible bits, others have tentacles and other appendages
on their heads to sweep the surface for detritus or collect detritus
suspended in the water. The fanworm has feathery tentacles to filter
food from the water.
Worm babies: While
some bristleworms can reproduce asexually by budding or dividing their
bodies into parts, most bristleworms reproduce sexually. Most bristleworms
have separate genders. In some, eggs and sperm are released into the
water simultaneously where they are fertilised. In many, the eggs
develop into free-swimming larvae that drift with the plankton before
settling down and developing into new bristleworms.
Ripping apart to reproduce! Some
bristleworms reproduce by epitoky: a portion of the bristleworm becomes
packed with eggs or sperm and becomes highly specialised for swimming,
some even developing eyes! This portion is called the epitoke. At
mating time, the epitoke breaks off from the main worm and can move
about on its own. Swimming to the surface, it is joined by the epitokes
of other bristleworms. At the surface, the epitokes burst apart, releasing
eggs and sperm for external fertilisation. In this way, the worms
can reproduce without exposing the rest of their bodies to danger.
However, while an epitoke might be a new segment produced by the animal,
sometimes the entire animal is remodelled into an epitoke and rips
itself apart during mating. Mating is usually triggered by the lunar
cycle. For a photo
of epitokes at the California
Academy of Sciences website.
Role in the ecosystem: Bristleworms
are eaten by many creatures higher up in the food chain. Shorebirds,
for example, depend on worms for sustenance to make their long migrations.
Human uses: Fishermen sometimes
dig out bristleworms to use as bait. |
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A red bristleworm
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See
also ...
Worms of Chek Jawa
Links
A Guide
To Singapore Polychaetes by Lim Yun Ping, the National University of
Singapore on the Acoustic Research Laboratory website: fact sheets and photos
of bristleworms found in Singapore.
Annelida,
Polychaeta
on the Canada's Aquatic Environments webpage on the University of Guelph
website: an easy introduction to the more technical aspects of their morphology,
metabolism, reproduction, ecology with an interesting section on their idiosyncracies
and photos.
Phylum
Annelida Class
Polychaeta on
Biomedia of the Glasgow University Zoological Museum on the Biological
Sciences, University of Paisley, Scotland website: a brief introduction
with explanations of the major classes, a glossary of terms and diagrams
and photos.
Worms
on Life on
Australian Seashores by Keith Davey on the Marine Education Society
of Australia website: an introduction to worms (annelids, sipunculids) with
explanations of the major parts of their bodies and their lifestyles. Check
out the animation of a predatory
annelid worm catching its prey.
Marine Sedentary
Polychaetes in Hong Kong on the City University of Hong Kong website:
about polychaetes and tubeworms, with fact sheets and photos on lots of
species.
Polychaetes
on the Big Bank Shoals of the Timor Sea on the Australian Institute
of Marine Science website: introduction to polychaetes in general including
epitoky.
Bristleworms
(Class Polychaeta) on the Chesapeake Bay Program website: fact sheet
on the worms and the species found in Chesapeake Bay.
Bristleworms
and their larvae by by Wim van Egmond on the Microscopy UK website:
lots of lovely super close look at the fascinating larvae of bristleworms
Other references
- Barnes, Robert
D. & Ruppert, Edward E., 1996. Invertebrate Zoology. Harcourt
College Publishers. 6th Edition. pp. 1056, G-1-16, I-1-30.
- Pechenik, Jan
A., 2000. Biology of the Invertebrates. McGraw-Hill Book Co.,
Singapore. 578 pp.
- Tan, Leo W. H.
& Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore
Science Centre, Singapore. 160 pp. online
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