The first visible abdominal sternum is completely separated by the hind coxae, which is one of the most easily recognizable traits of adephagans.

All families of adephagan have paired pygidial glands located posterodorsally in the abdomen, which are used for secreting chemicals.

The glands consist of complex invaginations of the cuticle lined with epidermal cells contiguous with the integument.

The secretory lobes differ structurally from one taxon to another; it may be elongated or oval, branched basally or apically, or unbranched.

The larvae are active, with well-chitinized cuticle, often with elongated cerci and five-segmented legs, the foot-segment carrying two claws.

The familial and tribal diversification of the group spans the Mesozoic, with a few tribes radiating explosively during the Tertiary.

Modern analysis has supported the clade Dytiscoidea instead, which includes many aquatic adephagans, notably excluding Gyrinidae.

[4][5][6] Cladogram of the relationships of living adephagan families after Vasilikopoulos et al. 2021[5] and Baca et al. 2021:[6] Gyrinidae Haliplidae Meruidae Noteridae Hygrobiidae Aspidytidae Amphizoidae Dytiscidae Trachypachidae Cicindelidae Carabidae (including former Rhysodidae)