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The jumping spider Phidippus audax.The basal parts of the chelicerae are the two iridescent green mouthparts. The chelicerae (/ k ə ˈ l ɪ s ər iː /) are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders.
The labrum is a flap-like structure that lies immediately in front of the mouth in almost all extant euarthropods, the general exception being provided by the probable chelicerate-relatives the pycnogonids. It has proved to be by far the most controversial of all arthropod head structures.
The Chelicerata are arthropods as they have: segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins; heads that are composed of several segments that fuse during the development of the embryo; a much reduced coelom; a hemocoel through which the blood circulates, driven by a tube-like heart. [9]
Sanctacaris is a Middle Cambrian arthropod from the Burgess Shale of British Columbia.It was most famously regarded as a stem-group chelicerate, a group which includes horseshoe crabs, spiders and scorpions, although subsequent phylogenetic studies have not always supported this conclusion. [1]
The subphylum Mandibulata constitutes one of the major subdivisions of the phylum Arthropoda, alongside Chelicerata. Mandibulates include the crustaceans , myriapods ( centipedes and millipedes ), and all true insects .
Hottentotta tamulus scorpion, showing telson. The term telson is widely used for the caudal spine of some chelicerates. [3] [4] The chelicerate telson can be clearly seen in a number of fossil species (like in eurypterids) and in extant animals (like the horseshoe crab "tail" and the scorpion sting).
Chasmataspidids, sometime referred to as chasmataspids, [2] [3] [4] are a group of extinct chelicerate arthropods that form the order Chasmataspidida.Chasmataspidids are probably related to horseshoe crabs and/or sea scorpions (Eurypterida), [5] [2] with more recent studies suggest that they form a clade with Eurypterida and Arachnida.
Merostomata is a class of chelicerate arthropods that contains the extinct Eurypterida (sea scorpions) and the extant Xiphosura (horseshoe crabs). The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by Henry Woodward to cover both groups.