Knoutsodonta jannae grows to 1,5 cm but is usually about 0,7 cm long. On the mantle are numerous stalked spiculate rounded tubercles (sometimes slightly pointed).
The mantle colour can be pale yellow or creamy white in in Canada and orange or lemon yellow in California. This species feeds exclusively on encrusting bryozoans of the genus Membranipora (Membranipora serrilamella and Membranipora membranacea).
Orange coloured Knoutsodonta jannae feeding on the orange coloured bryozoan Lyrula hippocrepis and yellow ones on Reginella mucronata.
Onchidoris muricata.was previously mistaken for Onchidoris muricata.