Even though the size of nematodes varies greatly, most nematode eggs are about the same size and shape. Most nematode species produce males and females, but some species only produce females. Male nematodes produce sperm in the testes which are shaped similar to the female ovary. Sperm accumulate in the seminal vesicle and exit through the anus. During mating rigid spicules insert into the vagina and form a passageway for the sperm.
Some males have thin cuticle extensions on both sides of the anus called bursae .
A few species produce male and female structures within the same individual. The most noticeable feature of the cuticle is the system of grooves across the body from head to tail. As nematodes grow they usually shed their cuticle four times. The tail is the region between the anus and the back tip of the nematode. Nematode species can be very difficult to tell apart so differences in the size, shape, and position of structures are used to identify nematodes.