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Fossil Focus: Chelicerata

Fossil Focus
by Jason A. Dunlop*1 Introduction: Chelicerata is one of the main divisions of the arthropods, and essentially consists of arachnids and their closest relatives. The name was coined in 1901 by the Berlin-based zoologist Richard Heymons (Fig. 1). It means the ‘claw-bearers’, in reference to the claw- or fang-shaped mouthparts that characterize the group. In addition to the arachnids, Chelicerata also includes the horseshoe crabs (Xiphosura), the extinct sea scorpions (Eurypterida) and little-known chasmatapaids (Chasmataspidida), and the sea spiders (Pycnogonida). The inclusion of sea spiders within this group is controversial, as we shall see below, and arachnids, horseshoe crabs, eurypterids and chasmataspids are sometimes grouped together as the Euchelicerata. The name Merostoma