This glossary describes the terms used in formal descriptions of spiders; where applicable these terms are used in describing other arachnids.
Abdomen or opisthosoma: One of the two main body parts (tagmata), located towards the posterior end; see also Abdomen: Other animals
Anal tubercle: A small protuberance (tubercule) above the spinnerets through which the anus opens
Apophysis (plural apophyses): An outgrowth or process changing the general shape of a body part, particularly the appendages; often used in describing the male pedipalp
Atrium (plural atria): An internal chamber at the entrance to the copulation duct in female haplogyne spiders
Bidentate: Having two teeth
Book lungs: Respiratory organs on the ventral side (underside) of the abdomen, in front of the epigastric furrow, opening through narrow slits; see also Book lungs
Bulbus → palpal bulb
Calamistrum (plural calamistra): Modified setae (bristles) on the metatarsus of the fourth leg of spiders with a cribellum, arranged in one or more rows or in an oval shape, used to comb silk produced by the cribellum; see also Calamistrum
Caput (plural capita): → cephalic region
Carapace: A hardened plate (sclerite) covering the upper (dorsal) portion of the cephalothorax; see also Carapace
Carpoblem: The principal tibial apophysis on the male pedipalp; also just called the tibial apophysis
Cephalic region: The front part of the cephalothorax, separated from the thoracic region by the cervical groove