Isoxys (meaning "equal surfaces") is a genus of extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators. It had a pair of large spherical eyes (which are the most commonly preserved feature of the soft-bodied anatomy), and two large frontal appendages used to grasp prey. Description Species of Isoxys have roughly semicircular bivalved carapaces, which vary in morphology between species. The front and rear edges of the carapaces bear foward and posterior facing spines, respectively which in some species are greatly elongated. The carapaces of Isoxys are typically in length, excluding the spines, though some species are known to reach over . In long-spined species when including spine length, some specimens exceed . The opening angle of the carapace was close to vertical, giving it a narrow profile when viewed from above. The head had a pair of large spherical stalked eyes, as well as a pair of upward-curling frontal appendages, which have a varying number of podomeres/segments, depending on the species. Most podomeres on the frontal appendages have endite spines, with the number and placement of spines varying between species. The last podomere of the frontal appendage is a curved terminal claw. The trunk lacks clear segmentation (arthrodization). Along the body are pairs of biramous appendages, the counts of which differ between species (Isoxys curvirostratus has 14, while Isoxys auritus has 11). The limbs have little differentiation from each other, and consist of endopods with well defined segments/podomeres, as well as exopods, which in specimens from the Chengjiang Biota have thick paddle-shaped lamellae which project perpendicular to the limb axis, while Isoxys volucris from Greenland has paddle-shaped expods fringed with setae. The end of the trunk has paired telson flaps. Ecology Species of Isoxys are thought to have been actively swimming predators, using its frontal appendages to capture soft-bodied prey, with the frontalmost pairs of biramous limbs aiding in food processing. The various Isoxys species are thought to have occupied a variety of niches, from swimming just above the seafloor (nektobenthic) to open ocean swimmers (pelagic). Swimming was likely accomplished by rhythmic movement of the legs. Eyes of different specimens appear to have been adapted to different light intensities; one specimen of I. auritus was either crepuscular in shallow water, or lived in waters around 140 m below the sea surface; whereas another was morphologically adapted to a diurnal light intensity