The top of the cephalothorax is protected by a chitinous layer known as the carapace. The underside is protected by the sternum at the back and a labium at the front. The size of the labium in proportion to the cephalothorax often varies among species, and is one of many ways that help distinguish between the families.
Body segments of a spider.
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The body of a spider is separated into two distinct regions: the cephalothorax (prosoma), which contains the stomach and brain, and to which all of the legs are attached, and the abdomen (opisthosoma), which contains the excretory system, silk glands, and a large part of the circulatory system. The cephalothorax and abdomen are joined by a narrow stalk known as the pedicel, through which the gut and blood vessels pass. It acts as a channel through which the two sections of the spider interact.
