An "'arthropod'" is an invertebrate animal defined by several morphological and biochemical features. Among these features are: segmented body covered by a hard exoskeleton, periodically molt (a process known as ecdysis), tagmosis, paired jointed appendages on varying segments, hemocoelic body cavity containing the hear, striated (for the most part) muscles, and epithelial tissue (which is usually non-ciliated).
Arthropods make up by far the majority of animal species, with more than a million currently described as estimates for as many as 9 million in total. Within the phylum Arthropoda are the classes commonly known as insects, crustaceans, arachnids (spiders and scorpions), and the extinct trilobites.
- Entomology. 2005. 3rd Edition. Cedric Gillott.