monotrocha

from The Century Dictionary.

• noun In chætopodous annelids, a larval stage with a single preoral circle of cilia.
• noun In Ehrenberg's classification, a prime division of Rotifera, containing those wheel-animalcules in which the wheel is single, continuous, and ciliated: distinguished from Sorotrocha, with compound or divided wheel. He divided them into two orders, Holotrocha and Schizotrocha, each of two families.
• noun In entomology, one of two great divisions of Hymenoptera, including those groups in which the trochanters have but one joint, proposed by Hartig in 1837.