Final answer:
Nematodes have a complete digestive and reproductive system, but lack circulatory, respiratory, and endo-skeletal systems.
Step-by-step explanation:
Among the options given, the organ systems found in Nematoda (roundworms) are the digestive and reproductive systems. Nematodes possess a complete digestive system, which includes a mouth, intestine, and anus. Their reproductive system can be either dioecious, with separate male and female individuals, or monoecious, with both male and female reproductive organs present in a single individual. Nematoda lacks a circulatory system and a respiratory system as they rely on diffusion to transport nutrients and gases across their body surface. They do not have an endo-skeletal system either, as their body structure is supported by the pressure of the pseudocoelomic fluid within their pseudocoelom.