INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERALLY SYMMETRICAL (BILATERIA) ANIMALS

SUBSECTION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM ARTHROPODS (ARTHROPODA)

SUBPHYLUM CHELICERATES (CHELICERATA)

A diverse group of Arthropods predominantly inhabiting land, with only about 5% of species dwelling in freshwater habitats or seas.

Characteristic Features of this subphylum generally include the division of the body into two tagmata: the cephalothorax (prosoma) and the abdomen (opisthosoma), along with the presence of six pairs of uniramous appendages on the cephalothorax. The first pair consists of chelicerae (from which the subphylum derives its name), which typically terminate in a pincer. The second pair comprises the pedipalps, or tactile palps. The remaining four pairs of appendages usually function as walking legs (locomotory limbs). In most chelicerates, abdominal appendages are absent; when present, they are modified to perform respiratory, reproductive, or other Functions.

The Digestive System of most chelicerates is characterized by paired glandular outgrowths of the gut known as the Liver. The excretory Organs are coxal glands (modified coelomoducts); terrestrial chelicerates additionally possess Malpighian tubules of entodermal origin. Respiratory organs in aquatic chelicerates are represented by gills on the abdominal appendages, whereas terrestrial forms utilize book Lungs and tracheae. A distinctive structural feature of the chelicerate Brain compared to other arthropods is the absence of the deutocerebrum.

The subphylum comprises three superclasses.