The Hairy Elysia or Elysia tomentosa is another cryptic sea slug — almost impossible to see as they generally take on the colour of the algae on which they feed. Some are a deep emerald green, some a dusty brown. Some have very noticeable flesh coloured margins; others have margins that are barely visible. There is a sedentary form and a migratory form (see Sea Slugs of Hawaii for more details regarding the difference). As you’ll see in the photos below a few are grazing or moving through the sea weed Caulerpa racemosa, one of their major food sources. Look for this bright circular algae in shallow protected reefs, on rocks and tide pools and you may be lucky enough to spot one. All these individuals were found in North Kihei or Ma’alaea Harbour, Maui. To 40 mm (1.5″) but most of the mature animals I have seen have been a little less than that.