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Chelicerates are in part defined by possessing chelicerate appendages, although crustaceans also possess chelate appendages. Chelicerates are more easily distinguished from other arthropods in lacking antennae and mandibles. Figure 4: Types of chelicerae: (A) jackknife, (B) scissor, and (C) 3-segmented chelate
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 .
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.
There is debate about whether Fuxianhuia from earlier in the Cambrian period, about , was a chelicerate. Another Cambrian fossil, Kodymirus, was originally classified as an aglaspid but may have been a eurypterid and therefore a chelicerate. If any of these was closely related to chelicerates, there is a gap of at least 43 million years in the ...
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 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.
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.
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.