Mites
Mites have been mighty fond of devolution. Free-living house dust mites descended from parasites which had evolved from free-living organisms.
More specifically, house dust mites speciated from mites that live in animal nests. Dust mites abandoned parasitism via digestive adaptation that allowed them to live off keratinous material, such as hair, feather quills, and flakes of skin.
Oribatids are an order of slow-growing mites with low metabolism. Many are soil saprovores. Some live in trees. Others are predatory. None are parasitic.
Some oribatid mites went from sexual reproduction to parthenogenesis before going back to having sex. Parthenogenesis predominates in soil mites, whereas sexual species colonize the bark of trees and mosses. Arboreal mites have a tougher time getting enough to eat, and so the diversity that comes from sex helps maintain populations.
