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CHELICERATES
"Spiders, scorpions, mites, ticks and horseshoe
crabs are all related and form a major branch called the chelicerates
within the Arthropod Phylum. All chelicerates live on land except
horseshoe crabs which are still living in the world's oceans.
Horseshoe crabs are living fossils. They are most closely related
to the extinct trilobites and also to another extinct group--the
sea-scorpions of the Paleozoic."
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| DR. NILES ELDREDGE, CURATOR, DEPARTMENT OF INVERTEBRATES |
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KNOWN SPECIES
Approximately 75,000; 750,000 estimated
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SIZE RANGE
Less than .1 millimeter to 60 centimeters
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WHERE THEY LIVE
On land; In estuaries and oceans; As parasites
on other animals
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ECOLOGICAL ROLES AND HUMAN USES
Parasites, predators, disease carriers
• Spiders and scorpions control pest populations (insects, rodents)
• Humans use horseshoe crabs as animal feed, as fertilizer, as a source of medicines,
and in medical research; Ticks, spiders, and scorpions are sources of medicines;
spiders are a source of silk
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