Some characteristics of Onychophora
The scientific name Onychophora means "claw-bearers" (Greek: όνυξ = nail/claw and φέρω = carry/bear) and refers to a pair of sclerotized claws on the tip of each leg , while the English name "velvet worms" highlights the velvety appearance of the water-repellent onychophoran body surface . The chitinous cuticle is moulted periodically, mediated by ecdysteroid hormones . Hence, onychophorans are typical ecdysozoans. Within the Ecdysozoa, Onychophora is united with Tardigrada and Arthropoda in the clade Panarthropoda , but the exact relationship of these three panarthropod groups is discussed controversially .
The overall anatomy of onychophorans has remained largely unchanged in the last 540 million years, as they resemble the Early Cambrian lobopodians, such as ✝Aysheaia pedunculata from the Burgess Shale formation in Canada and ✝Onychodictyon ferox from the Chengjiang fauna of China . The extant onychophorans share with the extinct lobopodians unjointed limbs (=lobopods), a soft body without an exoskeleton, and homonomous segmentation . Due to these ancestral features, onychophorans are an important outgroup for understanding the evolutionary changes that have taken place in the arthropod lineage.
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