Arthropoda are the most diverse living phylum
- comprise over half of all known species (> 1.2 million spp.)!
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They are protostomes, with a highly reduced coelom. -
They have an exoskeleton that must be molted in order to grow, both compound and simple eyes and jointed legs. -
They are segmented, but groups of segments are often combined into body regions (called tagmata), often specialized for particular tasks, such as movement or feeding. Organs and sometimes limbs are lost in particular segments as functions are divided among formerly independent segments.
Chelicerates (Subphylum Chelicerata)
- include horseshoe crabs and arachnids, such as spiders, scorpions and mites.
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Chelicerates are named for specialized front legs (chelicerae), which form the "fangs" of spiders. -
Chelicerates are important ecologically as predators and scavengers, and horseshoe crabs are important economically for medical testing
Crustaceans (Subphylum Crustacea)
- nearly all are aquatic and include shrimp, crabs and barnacles.
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Crustaceans typically have tougher, calcified shells and have the most diverse body forms of the arthropods, i.e. more highly varied tagmata -
Crustaceans are important economically as a food source
Myriapods (Subphylum Myriapoda)
- Myriapoda have similar segments over most of their body and superficially resemble annelids
- includes millipedes and centipedes and some smaller groups that serve as scavengers or predators in terrestrial food webs
Insects (Class Hexapoda)
- are the most diverse, speciose group known, with over 1 million species. They are also the most economically important invertebrate group.
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The study of insects is the field of entomology -
All have a three-part body plan (head, thorax, abdomen), modified mouthparts, and usually two pairs of wings and three pairs of legs, all on the thorax. -
They have successfully invaded most habitats except for saltwater. -
Major orders include grasshoppers, cockroaches and mantises (Orthoptera), dragonflies (Odonata), true bugs (Hemiptera), beetles (Coleoptera), butterflies and moths (Lepidoptera), flies (Diptera) and wasps, ants and bees (Hymenoptera). -
A major division exists between insects that have complete metamorphosis versus incomplete metamorphosis. -
Insects are important ecologically as predators, herbivores and scavengers, and form an important link in most food webs. Some insects are also important medically due to direct injury or as vectors of disease or economically due to crop damage
entomology
The study of insects
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