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Scorpion anatomy (morphology)
The scorpion's body, like that of
the spider, is divided into two main sections, the prosoma (cephalothorax) and the
opisthosoma (abdomen).
The prosoma is the anterior
(front) section covered dorsally (on top) by a hard sclerotized plate called the
carapace. The 8 eyes (varies from 0 - 10, depending on family, genus and
species) are situated, in 3 groups, on the carapace; a median pair
and two lateral groups of three.
The appendages are attached to
the prosoma, namely:
1) The chelicerae, jaws, are
used for feeding, grooming and digging (certain genera only, e.g. Opisthophthalmus)
and in the genus, Opisthophthalmus, to stridulate (rub together to make
a warning hissing sound).
2) The pedipalps are chelate (crab-like)
and consist of 6 segments are called the coxa, trochanter, femur, patella, tibia and
the tarsus. The tibia is referred to as the manus or hand, with the tarsus forming the movable finger. Combined they form the
chela (plural = chelae). The chela is equipped with
trichobothria and functions as a sensory organ and is used for holding prey,
defense, prey capture and in certain scorpions for digging burrows and
crushing prey.
3) The four pairs of legs each
comprise 7 segments, namely the coxa, trochanter, femur, patella, tibia,
basitarsus and telotarsus. At the end of the tarsus is the apotele,
which contains the ungues (claws). The coxa of the legs are enlarged protecting the
ventral (underside) surface of the prosoma.
The opisthosoma is divided into the
anterior mesosoma and a narrow caudal (tail) section known as the metosoma. A
sclerotized plate called the tergum covers each mesosomal segment dorsally and
the genital opercula are situated ventrally in the first segment (nearest the
legs). The second segment contains the pectines (comb-like sensory organs) while
the sterna, segments 3 – 7, have spiracles which, with the exception of the
seventh, open into booklungs.
The metosoma (tail) has 5
segments plus the distal (end) telson (stinger). The telson consists of a
round vesicle, which contains the venom gland and a pair of muscles, and
the aculeus (sting). Dorsally the metosoma has ridges and keels with the fifth
segment always the longest and containing sensory setaeous bristles. The anus is
situated ventrally just below the point it meets the telson.
The pectines situated ventrally
on the second mesosoma, are comb-like organs found only in scorpions. It has a
sensory function, the purpose of which is still unclear, but it appears that it
is used to detect pheromones or to determine the correct substrate to
deposit the spermatophore during mating (i.e. chemo- and mechanoreceptors).
Unique to scorpions is that the
cuticle fluoresces under ultraviolet light aiding in the collection and
observation of these interesting animals at night.
Scorpions are sexually dimorphic.
The females are usually larger and more robust than males while the male usually
has a longer tail. The pectines are smaller with shorter and straighter teeth in
the females. The chela is often longer and more slender in the male.
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Text by Norman Larsen ©. |
