Euchelicerata
| Chelicerata Temporal range: 445–0 Ma Late Ordovician (but see text) – present |
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| Horseshoe crab underside | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Clade: | Arachnomorpha |
| Subphylum: |
Chelicerata Heymons, 1901 |
| Classes | |
The subphylum Chelicerata (/kəˌlɪsəˈreɪtə/ or /kəˌlɪsəˈrɑːtə/; New Latin, from French chélicère, from Greek khēlē "claw, chela" and kéras "horn") constitutes one of the major subdivisions of the phylum Arthropoda. It contains the horseshoe crabs, sea spiders, and arachnids (including scorpions and spiders).
The chelicerata originated as marine animals, possibly in the Cambrian period, but the first confirmed chelicerate fossils, eurypterids, date from 445 million years ago in the Late Ordovician period. The surviving marine species include the four species of xiphosurans (horseshoe crabs), and possibly the 1,300 species of pycnogonids (sea spiders), if the latter are indeed chelicerates. On the other hand, there are over 77,000 well-identified species of air-breathing chelicerates, and there may be about 500,000 unidentified species.
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