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An Almost Arthropod: The Onychophoran

Onychoporans share certain characters with arthropods, but are lacking a hard exoskeleton or jointed legs. Onychophorans are probably closely related to arthropods and branched off the tree just before a fully hardened exoskeleton and jointed legs evolved.

Although not officially part of our arthropod story, they certainly deserve a closer look. These candy-colored animals can be bright blue, purple, orange, and green, and are covered in warty bumps. These carnivorous rain-forest dwellers have an unusual hunting style. They pursue small snails, worms, and insects and then shoot a glue-like substance at the intended victim, which quickly hardens and traps the prey.

onychophoran   onychophoran  
A couple of modern onychophorans

Onychophoran reproduction doesn’t necessarily involve much romance. In one South African onychophoran, males stick packets of sperm on the female’s body (apparently anywhere — leg, back, whatever!). Her body senses the sperm packet and dissolves the skin beneath the packet, allowing the sperm to enter her circulatory system and eventually reach her eggs.

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First onychophoran photo provided by Dr. Lynn Kimsey and the Bohart Museum of Entomology, University of California Davis; second onychophoran photo provided by M. J. Fouquette at the ASU Tropical Biology website