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The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind.<ref name="Biology">Template:Cite book</ref> (The terms prosoma and opisthosoma are equivalent to cephalothorax and abdomen in some groups. The terms prosoma and opisthosoma may be preferred by some researchers in cases such as arachnids, where there is neither fossil nor embryonic evidence animals in this class have ever had separate heads and thoraxes, and where the opisthosoma contains organs atypical of a true abdomen, such as a heart and respiratory organs.<ref>Template:Cite book</ref>) The word cephalothorax is derived from the Greek words for head ({{#invoke:Lang|lang}}, {{#invoke:Lang|lang}}) and thorax ({{#invoke:Lang|lang}}, {{#invoke:Lang|lang}}).<ref>Template:Cite book</ref> This fusion of the head and thorax is seen in chelicerates and crustaceans; in other groups, such as the Hexapoda (including insects), the head remains free of the thorax.<ref name="Biology"/> In horseshoe crabs and many crustaceans, a hard shell called the carapace covers the cephalothorax.<ref>Template:Cite book</ref>
Arachnid anatomyEdit
FoveaEdit
The fovea is the centre of the cephalothorax and is located behind the head (only in spiders).<ref name = dalton2008>Dalton, Steve (2008). Spiders; The Ultimate Predators. A & C Black, London. P.p. 19. Template:ISBN.</ref> It is often important in identification. It can be transverse or procurved <ref name = smith1990>Smith, A. M. (1990c). Baboon spiders: Tarantulas of Africa and the Middle East. Fitzgerald Publishing, London, pp. 138. Retrieved February 13, 2016.</ref> and can, in some tarantulas (e.g. Ceratogyrus darlingi) have a "horn".<ref name = gallon2008>Template:Cite journal</ref>
ClypeusEdit
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The clypeus is the space between the anterior of the cephalothorax and the ocularium. It is found in most arachnids.<ref name = smith1990/> It is connected to the labrum of the invertebrate, between the labrum and the face.
OculariumEdit
The ocularium is a "turret" for the ocelli found in most arachnids.<ref name = ynu>Spiders... Template:Webarchive Yorkshire Naturalists' Union. Retrieved February 13, 2016.</ref> In harvestmen, it may have the ornament of spines.<ref name = sankeysavory1974>Sankey, John & Savory, Theodore. British Harvestmen. Academic Press. P.p. 1–75. Template:ISBN.</ref>
TridentEdit
The trident is a small group of (usually three) spines found in harvestmen exclusively. It is located in front of the ocularium. It varies in size amongst species; in some it is completely absent, and in others it is enlarged considerably.<ref name = sankeysavory1974/>