Animalia Life

Arachnids belong to the phylum Arthropoda, and as such have the basic characteristics of this assemblage. These characteristics include having jointed appendages, an exoskeleton, an open circulatory system, and a ventral nerve cord. The Arachnida are a subgroup within the subphylum Cheliceriformes, those arthropods with a pair of primitively pincerlike chelicerae mouthparts. Arachnids are considered to have an aquatic origin, but most present-day forms are terrestrial in nature. Arachnids all have the following characteristics: a body that is divided primitively into a prosoma and an opisthosoma; a pair of chelicerae used as mouth parts, a pair of pedipalps that often end in pincerlike claws and are modified for prey manipulation and sperm transfer; four pairs of walking legs in the adult (juveniles may have three pairs) originating from the prosoma; absence of antennae; simple eyes in most; coxial glands at base of the legs and malpighian tubules extending between the hemocoels and gut tube used for excretion and osmoregulation; gut tube with diverticula; breathing accomplished by book gills (aquatic forms), book lungs, or tracheal tubes; and a dorsal heart. The following orders comprise the Arachnida: Scorpiones (scorpions), Uropygi (whip-tailed scorpions), Schizomida (schizomids), Amblypygi (whip spiders), Palpigradi, Araneae (spiders), Ricinuleids, Pseudoscorpionida (false scorpions), Solpugida (wind scorpions), Opiliones (daddy longlegs), and Acari (ticks and mites).

Arachnid Facts

Classification:
Kingdom: Animalia
Subkingdom: Bilateria
Phylum: Arthropoda
Subphylum: Cheliceriformes
Class: Chelicerata
Subclass: Arachnida
Geographical location: All continents
Habitat: Mainly terrestrial, with some few freshwater forms found among spiders
Gestational period: Extremely variable depending upon group or individual species
Life span: Variable, but some members may live up to twenty-five years
Special anatomy: All have eight legs as adults; pincerlike mouthparts that may be modified into fangs in some groups; most members are free-living but parasites are found among the Acarina; includes some of the most venomous animals of the world, such as the African fat-tailed scorpion, the American black widow spider, and the Australian red back and funnel web spiders

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