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The anterior of the two or three main divisions of the body of certain invertebrates, especially the cephalothorax of an arachnid.

[pro- + Greek sōma, body; see teuə- in Indo-European roots.]

pro·so′mal adj.


n, pl -mas or -mata (-mətə)
(Zoology) zoology the head and thorax of an arachnid


(proʊˈsoʊ mə)

n., pl. -mas, -ma•ta (-mə tə)
an anterior body region, esp. the arthropod cephalothorax.
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References in periodicals archive ?
Males in any population average about 80% of the prosomal width of the females (Shuster, 1979) and mature females are significantly heavier than mature males because of their larger size and added weight associated with numerous eggs within their prosomas (Leschen et al.