The penis of the
Opiliones (harvestmen) is an
intromittent organ that is not present in other
arachnids. It consists of a long shaft (the truncus) and a terminal capsule called a
glans, containing a
stylus and ejaculatory duct. It may have from one to three muscles, or none as in the specialized lineage
Grassatores, where the penis is operated by
haemolymph pressure. In some members of the
Cyphophthalmi, the structure has been termed a "spermatopositor".