ARTHROPODS: arthropod, (phylum Arthropoda), any member of the phylum Arthropoda, the largest phylum in the animal kingdom, which includes such familiar forms as lobsters, crabs, spiders, mites, insects, centipedes, and millipedes. About 84 percent of all known species of animals are members of this phylum.
CRUSTACEA
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jointed limbs, each often with two branches (termed biramous)
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seven or more pairs of appendages for feeding, swimming, walking, respiration and reproduction (clasping, sperm transfer, egg brooding and carrying young).
INSECT:
Insects are characterized by having three pairs of jointed legs from other arthropods; an abdomen that is divided into 11 segments and lacks any legs or wings; and a body split into three sections with one pair of antennae on the head (head, thorax, and abdomen). Sometimes, insects also have one or two wing pairs.
ARACHNIDS
Four pairs of legs (eight total). You can tell the difference between an arachnid and an insect because insects have three pairs of legs (six total).
Arachnids also have two additional pairs of appendages. The first pair, the chelicerae, serve in feeding and defense. The next pair, the pedipalps, help the organisms feed, move, and reproduce.
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The arachnid body is organized into the cephalothorax, a fusion of the head and thorax, and the abdomen.
To adapt to living on land, arachnids have internal breathing systems, like a trachea or a book lung.
Arachnids are mostly carnivorous, feeding on the pre-digested bodies of insects and other small animals.
Several groups are venomous. They release the venom from specialized glands to kill prey or enemies.
Several mites are parasitic, and some of those are carriers of disease.
Arachnids usually lay eggs, which hatch into immature arachnids that are similar to adults. Scorpions, however, give birth to live young.
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