Spider Anatomy

Arachnids have two body parts as opposed to insects with three. The first part is the prosoma and the second part is the abdomen.

The prosoma, usually referred to as the cephalathorax, as it consists of a fused cephalic (head) and thorax which may be separated by a distinct or indistinct cervical groove and the fovea, a depression to which the stomach sucking muscles are attached. The shape of the fovea and cervical groove are important diagnostic features for the identification of spiders into their respective taxa. Chitin is responsible for this part of the exoskeleton being hard and inflexible.

The prosoma houses various external appendages:

1	A pair of chelicerae with hinged fangs
2	A pair of pedipalps similar to the legs but with metatarsus absent. The palps are often used as a pair of arms and in adult males the tarsus develop secondary genitalia that give males the appearance of having boxing gloves. These copulatory organs are vary important in the identification of genera and species.
3	Four pairs of legs consisting of seven segments. apically is the coxa and trochanter (together forming the hip), the femur (thigh), the petalla (knee), the tibia ( shin or lower leg), the metatarsus (foot) and the tarsus (toes) with tarsal claws (toenails) at its end. The legs are use for locomotion and prey capture.
4	Dorsally the plate covering the prosoma is the carapace which contains the simple eyes, up to eight in various positions, an important identification character. The fovea a depression to which the stomach sucking muscles are attached is an important diagnostic feature for the identification of spiders into their respective taxa.
5	Ventrally the endites (pedipalpal coxa) and the labium (lip) form the mouth. The sternum (breast plate) with the dorsal carapace holds everything together. the two are joined by a pleurae, an elastic membrane. It is along the pleurae that the first crack stars the moulting process.

Internally the prosoma houses the central nervous system (brain), venom glands, the sucking stomach with part of the intestine and the muscles to control the appendages

The opisthosoma (abdomen), unlike the hard prosoma is soft and pliable. this allows the abdomen to expand when saturated with food or to house the developing eggs. Externally the abdomen contains:

1- Booklungs (a primitive breathing apparatus) are situated anterio-ventrally. Primitive mygalomorphae (baboon and trapdoor spiders) have two pairs, Araneomorphae one pair and a tracheal spiracle (a breathing apparatus as used by insects) and some advanced spiders have on tracheal spiracles. the posterior edge of the booklungs is situated on the epigastric furrow (fold) which house the spiders genitalia. Situated centrally on the epigastric furrow the adult female has a blackish scleritised epigyne. this epigyne is used in the identification of female spiders to generic and species level.

2- Posteriorly spiders have four to six spinnerets for the production of silk.

3- Above the spinnerets is the anal tubercle for the excretion waste products.

The opisthosoma contains the respiratory organs, heart, various spinning glands, the midgut, and ovaries for egg production.

Epigyne (epigynum) is the external genital structure of female spiders. As the epigyne varies greatly in form in different species, even in closely related ones, it often provides the most distinctive characteristic for recognizing species. It consists of a small, hardened portion of the exoskeleton located on the underside of the abdomen, in front of the epigastric furrow and between the epigastric plates.[1]

Calamistrum. The more or less extensive row of curved hairs on the hind metatarsi, used to comb the silk from the cribellum.

Carapace. The hard dorsal covering of the cephalothorax of a spider.
Cephalothorax or prosoma = A fused head and thorax. The united head and thorax of Arachnida and Crustacea.

Chelicerac. The pincerlike first pair of appendages of the arachnids; in spiders two-segmented, the distal portion or fang used to inject venom from enclosed glands into the prey.
Chorion. The outer covering or shell of the spider or insect egg.
Coxa. The basal segment of the leg by means of which it is articu- lated to the body.
Claw tufts. The pair of tufts of adhesive hairs present below the paired claws at the tip of the tarsi of many spiders.

Colulus. The slender or pointed appendage immediately in front of the spinnerets of some spiders; in other greatly reduced or seem- ingly missing; the homologue of the anterior median spinnerets or cribellum.

Coxal glands. The excretory organs of arachnids, in spiders located opposite the coxae of the first and third legs, that collect wastes into a saccule and discharge them through tubes opening behind the coxae; homologous with the nephndia of Peripatus, etc.

Cribellum. A sievelike, transverse plate, usually divided by a deli- cate keel into two equal parts, located in front of the spinnerets of many spiders; the modified anterior median spinnerets.

Cuticle. The hard outer covering of an arthropod.
Deutovum. The resting, spiderlike stage following the shedding of the chorion of the egg; the second egg.

Ecdysis. The process of casting the skin; molting.
Endite. The plate borne by the coxa of the pedipalps of most spiders, used to crush the prey; the maxilla.

Epigynum (female). The more or less complicated apparatus for storing the spermatozoa, immediately in front of the opening of the internal reproductive organs of female spiders.

Femur. The thigh; usually the stoutest segment of the spider's leg, articulated to the body through the trochanter and coxa and bear- ing the patella and remaining leg segments at its distal end.
Genitalia. All the genital structures.
Hackled band. The composite threads of the cribellate spiders, spun by cribellum and combed by the calamistrum.

Carapace = Carapace is a protective cover over the cephalothorax.
Chelicerae = The mouthparts of the of a spider. Chelicerae in spiders are hollow and contain venom glands, and are used to inject venom into prey.

Abbreviations :
AL= abdominal length, ALE= anterior lateral eye, AME=
anterior median eye, AW= abdominal width, CL= cephalothoracic length, CW=
cephalothoracic width, PLE= posterior lateral eye, PME= posterior median eye,
TL= total length.