Penis (Arachnida)

The penis of the Arachnida is an intromitent organ, present exclusively in the order Opiliones. It consists of a long shaft, the truncus, and a terminal capsule called glans, containing the stylus and ejaculatory duct. It may have from one to three muscles, or none in the specialized lineage Grassatores, where the penis is operated by haemolymph pressure.

This denomination refers to a superficial similarity (analogy) with vertebrate penises and does not have any phylogenetic relationship with it.