These dorids are feeding on the underlying Membranipora bryozoan. Also, their orientation, right shoulder to right shoulder, suggests that they are mating. Both species are commonly found on blades of giant kelp as seen here.
Here are two single males and a mated pair (younger male on older female) atop their host snail. Slipper snails are filter feeders and sequential hermaphrodites, first male, later female. There is no free-living larval stage; juveniles are pushed out from beneath their mother's foot. Depth 10 m.