Ultrastructure of the spicules of Pratylenchus penetrans.

The two spicules of PratyIenchus penetrans are not morphologically identical. The outer spicule is slightly larger and longer than the inner spicule. Each spicule is composed of a blade, shaft, and base. The spicules originate from the gradual thickening and invagination of the posterior walls of the spicular pouch. At the tip of each spicule are two small pores with one dendritic process associated with each pore. At the shaft portion, the spicule has a thick body which has a central core filled with nerve tissue. Dorsal and ventral wings project from the body. When protruded, the two wings of a given spicule curve toward the corresponding wings of the other spicule to form a complete tube for the conduction of sperm. The base of each spicule is composed of an electron-dense, sclerotized ring with nerve tissue in the central core. Each spicule is mobilized by two protractor and two retractor muscles. The posterior lips (=hypoptygma) of the cloaca are prominent and innervated. The vas deferens and rectum join near the cloacal opening.