Belinuridae
Belinuridae is an extinct family of arthropods belonging to the order Xiphosura, known from the latest Devonian, Carboniferous and Early Permian. They are placed as the only members of the infraorder Belinurina. They were one of the most successful and diverse groups of xiphosurans in their evolutionary history, having managed to colonise and diversify within freshwater environments particularly during the Carboniferous period.
Description
Belinurids are amongst the most morphologically diverse members of Xiphosura, exhibiting great diversity in body form across the group.The cephalothorax of belinurids are prominently domed, with the outer edges of the cephalothorax being flattened. The genal spines are either flat, project backwards, or even vestigial in some forms. The ophthalmic ridges, curve posteriorly relative to the position of the eyes. The thoracetron varies from triangular, to round to trapezoidal, which in Euproops and Belinurus are made up of 5-7 segments, though in some belinurid genera there are no visible segments/tergites on the thoracetron. The telson is narrow and elongate in all known belinurids.
Some belinurids exhibit a paedomorphic morphology resembling that of juvenile xiphosurans, with a reduced body size and reduced or absent genal spines, with a number of paedomorphic genera exhibiting a roughly equally sized cephalothorax and thoracetron.
Limbs including chelicerae are known from a number of belinurids, indicating that the limbs of the cephalothorax were arranged similarly to those of modern horseshoe crabs. The central nervous system in an exceptionally preserved specimen of Euproops is very similar to that of living horseshoe crabs and other chelicerates.