Scorpions are members of the phylum Arthropoda,
and more specifically of a subphylum of
that taxon known as Cheliceriformes. Scorpions
are members of the subclass Arachnida, those arthropods
having eight legs and chelicerae mouthparts,
and lacking antennae. Scorpions are the
oldest arthropod terrestrial group, whose aquatic
ancestry dates back to Silurian times over 400 million
years ago. Their terrestrial invasion occurred
in the Devonian period.
Scorpions are cosmopolitan in distribution, occurring
on all continents except Antarctica. Although
most people envision scorpions as desert
creatures, scorpions are found in the tropical jungles,
temperate forests, and savannahs and in
high elevations on mountains. They are mostly
nocturnal creatures as they have little defense
against the ultraviolet radiation of the sun. They
are quite variable in size: Some are as small as thirteen
millimeters, while others (the South African
Hadogenes troglodytes) range up to eighteen centimeters
in length.
Scorpion Physiology
Scorpions are segmental in form, the body being
divided into an anterior prosoma and a segmented
abdomen. A one-piece carapace covers
the prosoma. The abdomen is divided into a
preabdomen of seven segments and a postabdomen
of five segments, ending in a stinging apparatus.
The pedipalps are pincerlike and are used
to capture and hold prey. The chelicerae are pincerlike
as well and are used to macerate the prey.
There are four pairs of walking legs, all ending in a
pair of claws. All scorpions are carnivorous and
are essentially liquid feeders. Copious amounts of
digestive enzymes are poured over macerated areas
of the prey and the liquid is then pumped into
the stomach.
Scorpions are well equipped with sensory
structures. They have a pair of simple eyes located
in the center of the carapace. Additionally, there
are fromtwo to five pairs of eyes located along the
anterior and lateral margins of the carapace. Scorpions
have many setae or sensory hairs located
over the dorsal surfaces of the body. These hairs
function to pick up vibrations and air movement
and are used to detect prey. The hairs are large
on the pedipalps and are called trichobothria.
Unique to scorpions is a pair of ventrally located,
comblike appendages called pectines. These
structures are mainly chemoreceptors and are
used to pick up pheromone trails of insects.
Pectines are also used to dig burrows, although
the legs mainly perform this function.
Scorpions breathe by means of book lungs that
are ventrally located and open to the outside via a
pair of spiracles. In this way, the book lungs are
kept moist for oxygen diffusion.Acirculatory system
is present, with a dorsally situated heart that
opens via ostia or pores into the hemocoels and
book lungs. Scorpions are also well equipped
to deal with excretory wastes, using Malpighian
tubules. These tubules filter nitrogenous wastes
fromthe hemocoels and deposit the waste into the
gut tube for elimination.
Mating and Reproductive
Strategies
There are separate sexes and the gonads
are tubular in construction in
both sexes. The gonopore opens on
the ventral surface of the mesosoma.
Males lay a spermatophore sac that
is picked up by the female during a
courtship dance. This dance is initiated
by the male, who grasps the female's
pedipalps in his and dances
back and forth in a face-to-face position.
When the female touches the
opening lever of the spermatophore,
sperm are released. Fertilization is
internal, as is the development.
Scorpions are either ovoviviparous
or viviparous. The time from conception
to birth in scorpions is quite
variable. In some groups, birth requires
up to five months' gestation,
while in others the gestation period
can last up to eighteen months. In
viviparous species, the embryo is
fed via a tube that extends from the
digestive caeca to the embryos living
in the ovarian tubes. The juvenile
scorpions will exit the mother
via the gonopore and climb atop her back, where
they will mature and go through a molt. After this
first molt, they will take up their own independent
existence. Scorpions will molt from four to
seven times before they reach the adult stage. As
an adult no molting occurs, and limbs lost during
life are not regenerated.
Scorpion Fluorescence
Looking for scorpions is made easy by the fact that
scorpions will fluoresce under an ultraviolet black
lamp. Scorpions appear light green under ultraviolet
radiation. Fluorescence may be caused in part
by chemicals known as carotinoids that are found
in the epicuticle.
Classification:
Kingdom: Animalia
Subkingdom: Bilateria
Phylum: Arthropoda
Subphylum: Cheliceriformes
Class: Chelicerata
Subclass: Arachnida
Order: Scorpiones
Families: Bothriuridae, Buthidae, Chactidae, Chaerilidae,
Diplocentridae, Euscorpiidae, Hemiscorpionidae, Heteroscoripionidae,
Ischnuridae, Luridae, Microcharmidae, Pseudochactidae,
Scorpionidae, Scorpiopidae, Superstitioniidae,
Troglotaoysicidae, Vaejovidae, Urodacidae
Geographical location: Every continent except Antarctica
Habitat: Strictly terrestrial, found in both arid and tropical regions
Gestational period: Varies among species; lengths of between
five and eighteen months have been reported
Life span: Depending on the species, the life span may be only
one year, while other scorpions are known to live for twentyfive
years or more
Special anatomy: Eight legs, chelicerae mouthparts and simple
eyes like other arachnids; clawed pedipalps for grasping prey;
telson with a sting that can deliver venom; special sensory organs,
called pectines, that act in an olfactory capacity
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