Arthropods
Arthropods are characterized by a segmented body, exoskeleton, jointed appendages, open circulatory system, and a dorsal brain with a ventral nerve cord. A segmented body is called metamerization and in many arthropod groups, the segments have evolved into specialized distinct body regions. The exoskeleton of Arthropods are made chitin and usually hardened with scerotin (a protein) or calcium carbonate.When an Arthropod outgrows its exoskeleton, it undergoes a period of molting when it sheds its exoskeleton. Arthropods also have jointed appendages. "Appendages are structures such as legs and antennae that extend from the body wall." These structures include legs, sucking tubes, gills, jaws, antennae, etc. Arthropods also have a open circulatory system which means their blood is not completely contained in blood vessels. They also have a Dorsal brain which is a brain located at the front of the body. Along with the dorsal brain arthropods have a ventral nerve cord.
Arthropods reproduce sexually through internal fertilization and aquatic arthropods use external fertilization. During internal fertilization the males use reproductive organs to place sperm inside females or the male could deposit a sperm packet that is picked up by females. In the aquatic arthropods, the female releases eggs into the outside environment and males shed sperm around the eggs.
Some examples of Arthropods are
spiders
crabs
millipedes
butterflies
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Info:
Pretice Hall Biology book
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