The oribatid mite Ameronothrus lineatus (Thorell, 1871) is ovovivivparous in the high Arctic, i.e., larvae hatch from eggs within some hours after deposition. Earlier all Ameronothrus species have been considered larviparous, which implies that larvae hatch from the eggs inside the female. Proving ovoviviparity requires laboartory studies were newly deposited progeny are observed. Culturing congeneric species may reveal that A. lineatus is not the only ovoviviparous Ameronothrus species. Observations of cultures of A. lineatus showed that occasionally eggs with incomplete larval development were deposited. These eggs were observed at all constant laboratory temperatures (5-21 deg C), but most of them were found at 5 deg C. The majority of the eggs dried without any further development taking place, but 3 (out of 61) successfully hatched after 8-12 days at 15 deg C. This is the first record of mixed-parity mode in an ovoviviparous oribatid mite.