...asexual and sexual
Rotifers can have separate sexes, but much of the reproduction is by parthenogenesis.
The females involved in parthenogenesis are amictic and both their body cells and the eggs have diploid number of chromosomes. When conditions in the environments are probably not adequate (i.e. change in the type of food, temperature), mictic females appear.
The mictic female produces eggs that undergo the usual double meiotic division and are haploid. These eggs can then be fertilised by males, if the process is successful then a resting-egg is produced (an egg that has a thick wall). The resting-egg will hatch to produce an amictic female.
However, if a mictic female is not fertilised, she deposits eggs that promptly hatch into males.
In addition to parthenogenesis, sexual reproduction also occurs mostly in the Class Monogononta, while the order Bdelloidea is strictly parthenogenetic, no male bdelloid has ever been reported.