Cryptic is how Cory Pittman and Pauline Fiene describe the Thuridilla carlsoni in Sea Slugs of Hawaii.  I couldn’t agree more. One of these individuals was found in a tide pool in about  2″ or 5 cms of water, hiding in the algae. It blended in so well with its surroundings that it wasn’t until it disturbed a hermit crab that I actually noticed it. The other animal documented here was only found by dusting the algae on the surface of a rock. The novice  can easily mistake them for the Elysia degeneri, but their coral-coloured margin, deep lime green interior lines and red or coral tipped rhinophores differentiate the two. Both are spotted green on the lower exterior parapodia but the Thuridilla carlsoni has a much more intricate, leopard-like pattern.  To 25 mm (1″), but both animals photographed below were between 15 and 20 mm.  Found in the North Kihei and Sugar Beach area of Maui.