What organ systems are developed in roundworms? what functions do they perform?

Roundworms have the following organ systems:
1) The musculoskeletal system is presented in the form of a skin-muscle sac, necessary for movement, fixation of muscles and internal organs;
2) The mouth, intestines (three sections), anus are the sections of the digestive system, the function of which is the digestion of food and assimilation;
3) The products of metabolism of protonephridia and phagocytic cells (excretory system) are removed;
4) Regulates organs and systems of the nervous system: head ganglion, periopharyngeal ring, nerve trunks;
5) The reproduction function of round worms is possible due to the presence of the reproductive system.
These animals are heterosexual; male genital organs: testis – vas deferens – ejaculatory canal; female reproductive apparatus: paired ovaries – two tubular oviducts – paired uterus, connecting the vagina;
6) And there are no respiratory and cardiovascular systems.