The correct answer to this question is option 2 which includes statements I, II, and III.

Statement I is correct because tapeworms are indeed hermaphrodites, which means individuals carry both male and female reproductive organs.

Statement II is also correct since the roundworm species includes distinct male and female organisms, thus, round-worm has separate sexes.

Statement III indicates that filariasis, a disease affecting humans and animals, is caused by nematodes (roundworms). This is accurate as filariasis is indeed caused by infection with nematodes, specifically from the family Filarioidea.

Statement IV, however, is incorrect. Guinea-worm, also known as Dracunculus medinensis, is a type of nematode, not an annelid. Annelids are a completely different phylum of animals, which includes earthworms and leeches. Therefore, only the first three statements are correct, making option 2 the correct answer.