prosoma
noun
pro·so·ma (ˌ)prō-ˈsō-mə 
: the anterior region of the body of an invertebrate (such as an arachnid) especially when the segmentation is suppressed or obscured
especially : cephalothorax
Example Sentences
Recent Examples on the Web When a spider wants to straighten its legs to move, the prosoma section (where its legs attach to its body) ejects fluid into the legs, pushing them out straight. 
Manasee Wagh, Popular Mechanics, 28 July 2022 The head, or prosoma, houses most vital organs, including the heart and the brain. National Geographic, 20 Apr. 2020
Manasee Wagh, Popular Mechanics, 28 July 2022 The head, or prosoma, houses most vital organs, including the heart and the brain. National Geographic, 20 Apr. 2020 Word History
Etymology
New Latin, from Greek pro- + sōma body
First Known Use
1853, in the meaning defined above