Anatomy

Tarantulas, like all spiders, have a exoskeleton made of chitin. They got eight legs and two pedipalps which are used for grabbing the food items, for touch and in mating. On each leg the last segment, the tarsus, have two or three claws used for climbing. On each legs tarsus and metatarsus there is tufts or hair called scopulae which enables the tarantula to grip the surface and even climb very smooth surfaces. The end part of the spider is called abdomen and the front part cephalothorax, and the top of the cephalothorax is called carapace. All tarantulas got eight eyes located on top of carapace with the exception of the mexican cave living genus Hemirrhagus (see pictures below) in which some species completely lost their eyes. Below the eyes are the chelicera with fangs and the mouth parts. The stomach and respitory organs, called booklungs, are located in the abdomen. The size of theraphosids varies from c:a 2 cm Aphonopelma paloma to Theraphosa blondi that measures 25 cm in legspan.

Dorsal view

Dorsal view

I – leg 1
II – leg 2
III – leg 3
IV – leg 4
a – carapace
b – chelicarae
c – pedipalp
d – abdomen









Carapace

Carapace

a – eyes
b – fovea








Ventral view

a – chelicerae with fangs
b – maxillary lobe
c – labium
d – sternum
e – anterior booklung
f – epigastric furrow
h – posterior booklung
i – spinnerets











Leg 1

LEG I

a – coxa
b – trochanter
c – femur
d- patella
e – tibia
f – tibia spurs
g – metatarsus
h – tarsus
i – claws

At the end of the abdomen are the anal and the spinnerets. Tarantulas look hairy and most american species got so called urticating hair on their abdomen for defense. Its not hair like mammal hair growing out of a hair sack, but protusions from the exoskeleton.  Urticating hair is a common and accepted term for setae which are the correct name.

The urticating hair is located on the top of the abdomen on a patch and kicked off by rubbing the back legs. The rubbed off hair penetrates skin and mucous membrane of the aggressor which cause discomfort and will most likely deter further attacks. The same hair are also used to cover eggsacks and to cover the entrance of the burrow. Some of the hair on the tarantulas legs are used for locating food, aswell as picking up particals in the air to sense the temperature and humidity. The Old World species lack urticating hairs and primerely use the chelicera for defense. Atleast one american genera, Ephebopus, have urticating hair located on the pedipalps.

Above: Hemirrhagus reddelli © Martin Nicholas

Above left to right:  Avicularia avicularia. The red colored area is the claw tufts.
Most members of the genus Ceratogyrus have a foveal protuberance (or ”horn”). Another tarantula that have a similar protuberance is Sphaerobothria hoffmanni Karsch, 1879, in Costa Rica.

External links

Wikipedia urticating hair

About the Author