Q: What is the Bizarre Worm
Bazaar?
A: An information resource
for researchers using and/or looking for certain nematode cultures. It
consists mainly of a list of the species that I have (had) in my culture
collection. A datasheet is provided for each strain, with origins, classification,
literature, etc. of that strain. Most strains are freely available for
reasearch purposes, some are lost, and some are only conditionally available.
This is not a sales catalog. I do not charge for sending cultures,
but I do hope (and in some cases will verify) that requests are only for
use of these nematodes in genuine research.
The Bazaar also has pictures of some of the listed
strains, to illustrate some of the many different appearances of these
and other nematode species. If you wish, you are free to download the files
in question, but only for non-commercial purposes, and (if they are to
be used in a publication) with the proper attribution to the original source.
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Q: What are worms?
A: Any invertebrate animal
with elongate body and no obvious legs or wings. The
word "worm" is a bucket term - it groups many different kinds of animals
that are not necessarily related to one another, e.g. flatworms (Turbellaria),
tapeworms (Cestoda), roundworms (Nematoda), earthworms (Oligochaeta), etc.,
etc. Thus, different kinds of worms really have very different biological
properties, e.g. some flatworms and earthworms can regenerate large parts
of their body, but no nematode is capable of such a feat.
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Q: What are nematodes?
A: Nematodes are an extremely
diverse group of worms with a characteristic body plan that includes several
remarkable anatomical and biochemical characters. They
are pseudocoelomate, unsegmented protostomes
with a mixture of hexaradiate,
triradiate and bilateral
body symmetry and with a life cycle passing through several moults. The
body wall of nematodes consists of four sectors with muscles that are neither
transverse nor exactly longitudinal, but rather longitudinally oblique.
Unlike nearly all other multicellular animals (Metazoa), nematodes have
muscle cells that reach out to nerves rather than vice versa. Nematodes
also have some very unusual physiological capacities that are not known
in other Metazoa. For instance: nematode messenger RNA (a type of molecule
involved in the expression of genes) receives a transspliced leader
sequence. Nematodes are capable of autonomous synthesis of poly-unsaturated
fatty acids (i.e. the more healthy kind of fatty acids, which animals
like us must obtain from food). The metabolic arsenal of nematode includes
a glyoxylate cycle (an alternative mechanism for converting stored
body fat into sugars).
Bilateral: Having one transverse axis of
symmetry. The entire human body bilaterally symmetrical in most respects,
but one hand or foot by itself is not.
Hexaradiate: Having six transverse axes
of symmetry (e.g. like each cell in a beehive, or like the playing board
for chinese checkers). All hexaradiate objects are necessarily also triradiate,
whereas all triradiate objects are not necessarily hexaradiate.
Protostome: An animal in which the mouth
has developed directly from the earliest embryonic "mouth" or blastopore.
The alternative condition is called deuterostome, where the mouth
develops secondarily from an opening that is not the blastopre, but lies
at the other end of the embryonic gut from the blastopore.
Pseudocoelomate: An animal with a body
cavity that is not a true coelom, i.e. it lacks an epithelial lining enveloping
all organs and covering the internal surface of the body wall.
Triradiate: Having three transverse axes
of symmetry (e.g. like the icon for radioactivity, or like a fully opened
camera tripod)
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Q: How diverse are nematodes?
A: Nematodes may well be
the most diverse group of multicellular animals.
Unfortunately, most text books haven't got a clue, so repeat this sentence
three times before you read on: PERHAPS
THE MOST DIVERSE GROUP OF ANIMALS (x3).
No one knows even approximately how many species of nematodes currently
exist on earth, but published figures range from less than 100,000 to 100
million - a difference of three orders of magnitude. The 100 Megaspecies
estimate has given rise to the somewhat dubious statement that "four out
of every five animals is a worm, and the fifth is a beetle". In reality,
there is as yet no reliable way of estimating the total number of living
insect species, and much less so the numbers of species of nematodes, fungi,
mites, protozoans, bacteria, etc., etc. All we really know is that the
estimated numbers for all these "creepy-crawlies" continue to increase
drastically, as we assess more and more of their genetic diversity, rather
than just their poorly visible morphology and anatomy. Most published figures
for the number of living species of organisms may well be far below
the mark, and nematodes are a significant chunk of the hidden part
of this taxonomic iceberg.
"Nematodes diverse? Well maybe so, but they're
still a uniform lot, aren't they?" Not on your life - this myth is largely
based on the very few species that have been studied in greater detail.
Most nematodes are worm-shaped, just like most insects have a body consisting
of three main parts, or most tetrapod vertebrates have four limbs, but
otherwise there are no bounds on their ecological, developmental, anatomical,
biochemical and cytological diversity. Don't start me to talkin'...
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There are huge nematodes (8 meter long) and minute
nematodes (less than a quarter of a millimeter long). There are spherical
nematodes, octagonal nematodes and asymmetrical nematodes. There are nematodes
that look like miniature pinecones, dragons, hedgehogs, caterpillars or
bottle-brushes. The head of a nematode can look like an orchid, a suction
cap, a cactus, a crab, a medieval helmet, the head of an elephant or the
head of a catfish. Nematode morphology is extremely diverse - when
viewed with the proper tools and magnification.
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Nematodes swim, crawl, jump, walk on stilts, or float
on the wind like dust particles. Nematodes eat bacteria, soil algae, protozoans,
eggs, other nematodes, yeast, fungi, plant cells and animal tissues. There
are nematodes in soil, water, vinegar, moss, roots, wood, figs, seeds and
the bodies of both dead and living animals. There are nematodes in the
microchannels of polar ice, in the anaerobic sediments of the deepest oceans,
and in the parched sands of the hottest deserts. Non-parasitic nematodes
are often described as basically aquatic animals, but it is more correct
to describe them as essentially interstitial organisms specifically
adapted to life at the interface of solid, liquid and (often) gaseous matter
in soils and sediments, and dominating interstitial ecosystems in numbers
and diversity.
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The larvae of certain nematode species seek out the
pupae of certain fly species, and patiently sit on its head until the fly
hatches - waiting to hitch a ride to the next microhabitat. The larvae
of other nematodes invade soil-inhabiting insects, release toxic bacteria
that kill the insect, and then feast on both the bacteria and on the dead
insect's remains. Nearly every kind of animal and plant has one or more
species of nematode parasites. And that includes humans - and nematodes.
Some parasites invade their host through the mouth and migrate through
lungs, muscle and various other organs - the trajectory depends on the
species - only to finally re-enter the digestive system and settle for
maturation in the gut.
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Nematode embryos can develop over weeks or months,
with long periods of apparently random cell movements - or nematode embryos
can develop in less than one day, in a rigidly programmed avalanche of
highly determinate divisions. Some nematodes have simple block-shaped cells
throughout their bodies, but others exhibit advanced compact design,
quite befitting of a microchip, with many compressed cell parts tightly
packed in the head, while the voluminous nuclei of these cells are located
elsewhere in the body.
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Genetically, the diversity within nematodes far exceeds
that of many other groups of animals. In terms of the sequence of genes
coding for the ribosome (one of the most conserved building blocks
of the chemistry of life), very closely related nematode species are as
different from one another as a monkey and a mouse. In fact, a few nematode
species have reinvented big chunks of the ribosome, and these are so different
that they cannot be recognised as parts of the ribosome, even when compared
to other nematodes.
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