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Tetrophthalmi
Tetrophthalmi is an extinct suborder of Opiliones (commonly known as harvestmen or daddy longlegs) that had four eyes. First described in 2014, it is known from two extinct species. Phylogenetic analysis suggests that four eyes is the ancestral condition for harvestmen, placing Tetrophthalmi and Cyphophthalmi in a basal position within Opiliones.
==Classification history==
In the early 1980s, a tiny fossil was extracted from the Montceau-les-Mines Lagerstätte deposit in Eastern France. The fossil went unstudied for more than 30 years before paleontologist Russell Garwood used x-ray computed tomography (CT scans) to investigate the fossil. In 2014, a team led by Garwood identified the specimen as a novel species, ''Hastocularis argus'', named for the 100-eyed giant Argus Panoptes in Greek mythology.〔http://m.csmonitor.com/Science/2014/0411/Ancient-four-eyed-wonder-resolves-daddy-longleg-mystery〕 According to their analysis, the specimen died in some sedimentation approximately 305 million years ago. Before it decayed, its body was surrounded by the mineral siderite, which formed a protective concretion. The specimen subsequently decayed, leaving a void showing a detailed outline of the creature.
The CT scan revealed that ''H. argus'' had two sets of eyes - one set mounted on the ocularium in the middle of head and one set on its side on the stink glands. Performing comparative analysis on 158 morphological features, Garwood's team determined ''H. argus'' was closely related to ''Eophalangium sheari''.〔 The two species were not, however, as closely related to the 270 other species of harvestmen studied. The team determined ''H. argus'' and ''E. sheari'' shared three features – two pairs of eyes, an open gonostome (a part of the reproductive system), and external male genitalia – which distinguish them from all other harvestmen. Thus, the two species were classified into a new suborder, Tetrophthalmi.〔
''Hastocularis argus'' and the new suborder Tetrophthalmi help explain how arachnid eyes developed. The classification also helps clarify when side-eyed and fore-head eyed harvestmen split into distinct clades.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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