Characteristics of Arthropods
General Characteristics
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Segmented
Jointed appendages
Hard external skeleton
3 parts-head, thorax, abdomen
(arachnids exception)
Exoskeleton-hard, external skeleton made
of chitin
o
Molting- shed old
exoskeleton and secrete a
larger one, very vulnerable
after molting
Digestive System
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Complete digestive tract (mandible-chewing or proboscis- sucking) with a dorsal heart and a ventral nervous
system
Respiration
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Respiration through gills, trachea, book lungs or body surface
Sensory
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Sensory organs include antennae and hairs, simple and compound eye
Reproduction
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Reproduces (mostly sexually), one to several larval stage
Movement
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The muscle system is more or less assisted by hydraulics originated from the blood pressure created by the heart
Circulation
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with open circulatory system. Haemolymph that contains haemocyanin, a copper-based oxygen-carrying protein
Four SUBPHYLA of Arthropods
Trilobita – thought to be the oldest arthropods
Chelicerata – two part body and mouthparts called chelicerae
Crustacea – hard exoskeleton, two pairs of antennae, mouthparts called mandibles
Uniramia – contains more species than all other groups of animals alive today
ARTHROPODS ARE SUCCESSFUL ANIMALS
From nature's point of view, the combination of being joint legged
and not having a backbone seems to be a good one,
because arthropods are the most successful group of animals on
earth! The chart shows just how successful. It shows that the
number of arthropod species on Earth is far greater than the number
of species of all other kinds of animals. Scientists believe that 46 millionarthropod species exist.
The word "successful" needs to be defined, for many humans would
consider mammals to be earth's most successful group of animals, since humans are
mammals, and humans are obviously Earth's "top dogs." However, the human standard
for "success" isn't necessarily the only one. From a biological perspective, animal groups
are "successful" if...
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they include a large number of species
the species occupy many different kinds of habitats
the species eat many kinds of food
the species are good at defending themselves from their enemies
In these terms, humans don't look particularly successful. For one reason, there's just one
species of us. If we do something really dumb and end up going extinct, there won't be
another human-like species to evolve into the brain-using "niche" we're presently
occupying. Current thought is that during the evolution of the human species there have
been several species of the genus Homo -- several kinds of humans, such as the
Neatherthals -- but the other human kinds went extinct (like the Neatherthals), possibly
because we Homo sapiens killed them off.
Moreover, there's still a big question as to whether we'll ever overcome our enemy -which is ourselves. Shall we destroy ourselves in nuclear or biological war, or by
continuing to poison the earth with our pollution? It's often said that if anything can survive
a nuclear holocaust or a poisoned earth, it's a cockroach. And cockroaches are insects,
which are arthropods!
ARTHROPOD EVOLUTIONARY ADVANCES
What makes arthropods so successful? Here are some of the most obvious evolutionary
advances that arthropods show over the simpler, more "primitive" mollusks and
segmented worms:
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Jointed legs give arthropods more mobility on dry land than mollusks and worms have
Arthropod body segments are more specialized than annelid segments, so arthropods enjoy a
greater range of possible activities and behaviors than do segmented worms
The arthropods' exoskeleton reduces water loss from their bodies much better than the
annelids' cuticle and the mollusks' thin skin