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The arthropods ancestrally possessed compound eyes, but the type and origin of this eye varies between groups, and some taxa have secondarily developed simple eyes. The organ's development through the lineage can be estimated by comparing groups that branched early, such as the velvet worm and horseshoe crab to the advanced eye condition found in insects and other derived arthropods. Apposition eyes are the most common form of eye, and are presumably the ancestral form of compound eye. They are found in all arthropod groups, although they may have evolved more than once within this phylum.〔 〕 Some annelids and bivalves also have apposition eyes. They are also possessed by ''Limulus'', the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point.〔 Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion. ==Eyes and functions== Most arthropods have at least one of two types of eye: lateral compound eyes, and smaller median ocelli, which are simple eyes.〔 When both are present, the two eye types are used in concert because each has its own advantage. Flying insects can remain level with either type of eye surgically removed, but the two types combine to give better performance.〔 Ocelli can detect lower light levels,〔They are about 5000 times more sensitive than apposition compound eyes. They can, for instance, respond to the position of the full moon〕 and have a faster response time, while compound eyes are better at detecting edges and are capable of forming images.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「arthropod eye」の詳細全文を読む スポンサード リンク
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