Type of roundworms, how do males differ from females?

Roundworms (or Nemata) are animals that are often sexually dimorphic. In the internal structure: in males, the reproductive system is represented by testes, vas deferens and ejaculatory canal (sometimes there are copulatory organs – spicules), and in females – by ovaries, oviducts, uterus, vagina and genital opening.
In external structure: females are larger, and males have a more rounded back section.