This is the smallest suborder of nudibranchs. The gills appear as cerata, except in Arminia where they are found below the mantle. Dirona has a wide, undulating oral veil or velum on the head, while in Janolus the numerous cerata extend anterior to the rhinophores. 

Arminia is found on sand bottoms foraging for sea pens and the sea pansy, Renilla.