Adults of the aquatic coptoclavid beetles (Coleoptera: Adephaga: Dytiscoidea), described from four Middle Jurassic fossil localities in Inner Mongolia and Liaoning in northeastern China, are attributed to Daohugounectes primitives Wang, Ponomarenko and Zhang, 2009, which was previously proposed after study of larvae. The generic name Timarchopsis Brauer, Redtenbacher and Ganglbauer, 1889 is proposed as a substitute for the preoccupied and junior homonym Necronectes Ponomarenko, 1977, non Milne-Edwards, 1881. Furthermore, the subfamily name Necronectinae Ponomarenko, 1977 is substituted by the available name Timarchopsinae. Daohugounectes is placed into Timarchopsinae because its adults have long, slightly apically widened tibiae and small femoral plates. The adults of this genus differ from those of other Timarchopsinae in the following features: antennae short and widened in the middle part; basal segments of protarsi not cut apically; metaventrite with a triangular plate. The larvae look like somewhat primitive forms in the subfamily Timarchopsinae. In contrast to these primitive larvae, the adults with some advanced characters can be regarded as among the most advanced forms in the subfamily Timarchopsinae, and probably represent a transition between the Timarchopsinae and Charanoscaphinae. Such mosaic evolution within Daohugounectes indicates that the evolutionary process of aquatic beetles is far more complex than previously thought.