Isoxys

Isoxys Temporal range: Atdabanian to Paibian PreЄ Є O S D C P T J K Pg N
Isoxys sp., 24mm
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Megacheira?
Family:	Isoxidae?
Genus:	Isoxys Walcott, 1890
Species
I. chilhoweanus Walcott, 1890 (type) I. acutangulus (Walcott, 1908) I. auritus (Jiang, 1982) = Cymbia aurita I. bispinatus Cui, 1991 I. carbonelli Richter & Richter, 1927 I. communis Glaessner, 1979 I. curvirostratus Vannier & Chen, 2000 I. glaessneri García−Bellido, Paterson, Edgecombe, Jago, Gehling & Lee, 2009 I. longissimus Simonetta & Delle Cave, 1975 I. minor I. paradoxus Hou, 1987 I. volucris Williams, Siveter & Peel, 1996 I. wudingensis Luo & Hu, 2006 I. zhurensis Ivantsov, 1990

Isoxys is a genus of extinct, pelagic bivalved arthropod; the various species may have been free-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 appendages, which have led to speculation that it may be related to the great appendage arthropods.

Isoxys was abundant in tropical seas, and may have had a global distribution. 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 in shallow waters. It is likely that Isoxys was a visual predator that hunted swimming above the seafloor. It had powerful prehensile frontal appendages and large spherical eyes. Isoxys could propel itself by the beating possibly 14 flippered swimming legs (setose exopods) and steer with a flap-like tail (or telson).

There are a number of species of Isoxys. I. volucris is the most abundant in the Sirius Passet locality; I. auritus is found in China. In addition to a single specimen of I. longissimus, 163 specimens of I. acutangulus – making a total of 164 specimens of Isoxys are known from the Greater Phyllopod bed, where they comprise 0.31% of the community.