Opiliones anatomy

Opiliones are an order of arachnids and share many common characteristics with other arachnids. However, several differences separate harvestmen from other arachnid orders such as spiders. The bodies of opiliones are divided into two tagmata : the abdomen (opisthosoma) and the cephalothorax (prosoma). Unlike spiders, the juncture between the abdomen and cephalothorax is often poorly defined. Harvestmen have chelicerae, pedipalps and four pairs of legs. Harvestmen were traditionally thought to have two eyes, except in the case of eyeless species. Developmental genetic work has shown that living species retain up to six eyes, including one pair of rudimentary median eyes and one pair of rudimentary lateral eyes.

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