Phylum: Arthropoda

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This crab lives near a seafloor volcanic vent in water that is 230 degrees C.!

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Arthropods are invertebrates with a tough exoskeleton, jointed appendages, and a segmented body. The exoskeleton is made of chitin, and when combined with calcium carbonate, becomes very hard. Arthropods typically have very many appendages, and bodies divided into anywhere from two to dozens of segments.

Based on the various animals' mouth parts, many taxonomists divide the phylum arthropoda into two subphyla: Chelicerata and mandibulata.

Chelicerata

The chelicerates have mouth parts called chelicerae. Chelicerae are typically fang-like, and used for piercing and sucking. Chelicerates also have another pair of mouth parts called pedipalps, which feel and manipulate the food. Chelicerates also lack antennae, and have a two body segments.

Some of the animals belonging to the chelicerates are the arachnids and horseshoe crabs.

Class: Arachnida

Arachnids have four pairs of legs. This class includes spiders, ticks, mites, and scorpions. Scorpions are unusual in that their pedipalps have been modified into pincers.

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Horseshoe Crabs

Horseshoe crabs are often put in a class by themselves: merostomata. They differ from other chelicerates in that they have five pair of legs, and additionally have a hard, shield-like shell and long tail spine.

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Mandibulata

Mandibulates have mouth parts called mandibles, which are typically useful for grinding food. Mandibulates include crustaceans, insects, millipedes, and centipedes. Some taxonomists prefer to put the the insects, millipedes, and centipedes together in a subphylum called uniramia, and also classify crustacea as a subphylum, while other taxonomists simply list them all a level down as classes.

Class or subphylum: Crustacea

Crustaceans are typically aquatic, have two pair of antenna, and two or three body segments. In crustaceans, the chitin in the exoskeleton is often combined with calcium carbonate, making it very hard.

Some common crustaceans are crabs, lobsters, crayfish, shrimp, pillbugs, and barnacles.

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Subphylum: Uniramia

Uniramians include the insects, centipedes, and millipedes.

Class: Insecta

Insects have three pair of legs attached to the middle segment of a three-segment body. Insects also have one pair of antennae. Some common insects are ants, bees, termites, grasshoppers, beetles, butterflies, moths, flies, and dragonflies.

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The Bullet ant, so called because to be stung by one feels as if you've been shot!

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The Velvet ant (actually a wingless wasp), also called the Cow Killer, because it's sting is so painful it is said it could "kill a cow".

Classes: Chilopoda and Diplopoda

The chilopods are the centipedes, which have only one pair of legs per body segment in a long, worm-like body of many segments. Centipedes are carnivorous, hunting and killing their prey with poisonous pincers.

The diplopods are the millipedes, which have two pair of legs per body segment in a long, worm-like body of many segments. Millipedes feed on decaying plant matter, and can exude poison from their shells as a defense.

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