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Phylum Arthropoda - Arthropods

springtail - Orchesella cincta Moth - Morrisonia latex bee? - Osmia ribifloris Midge with Mite - Tanypus Ephemerella dorothea infrequens - voucher specimen, in alcohol - Ephemerella dorothea Conophthorus ponderosae Gaurotes cyanipennis Nymph - Lygus
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Explanation of Names
from the Greek arthron (αρθρον)- "joint" + podos (ποδος)- "of foot, leg"; refers to the jointed legs of all members in the phylum
Numbers
Worldwide:(1)(2)
15 classes
>120 orders
~2140 families [doesn't sound right, as Crustacea alone have >1000, Myriapoda close to 200, Arachnida and Hexapoda close to a thousand each, too... =v=]
>1.3 million described species (plus many more undescribed)
Size
ranges from the smallest mite (about 0.10 mm) and the smallest insect (a Hymenopteran, Dicopomorpha echmepterygis at 0.139 mm), up to the King Crab (legspan more than 3.5 m), but most arthropods are in the range 2-25 mm
Identification
Three or more pairs of jointed legs (some mites have less, many insect larvae have none)
Body segmented, bilaterally symmetrical
Possessing an exoskeleton, usually tough, composed in part of chitin(2)
See Glossary for terminology.
Range
Cosmopolitan
Habitat
Almost every habitat
Internet References
Introduction to the Arthropoda (Waggoner & Collins)
Tree of Life (Maddison 1995)
Insect Morphology (illustrated glossary)