See text Janolus is a genus of small to large sea slugs, or more accurately nudibranchs, marine gastropod mollusks, in the family Janolidae.

[2] The name Janolus is derived from the two-headed god Janus, in ancient Roman mythology.

Janolus species are found in many areas world-wide, including Europe, Australia, Japan and Africa.

This genus of nudibranch is found in shallow and subtidal waters.

When Janolus is about to be caught, it rolls into a ball, leaving its cerata exposed.