Sexual head structures in the onychophora: Unique modifications for sperm transfer

An extensive diversity of male extra-genital sexual structures is described from eleven recently discovered species of onychophorans from Australia. These organs are located on the dorsal surface of the head and are highly elaborate in some species. They range from a patch of variously modified dermal papillae to a deep pit adorned with hardened hooks, spikes or hollow stylets. We propose that these hardened structures are also derived from dermal papillae. In two species, spermatophores have been observed within the organ and it is speculated that they function in the mechanics of sperm transfer.