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
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.
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.
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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