This is one of several small nudibranchs that are difficult to tell apart from a distance.  For the novice, it seems especially close to the Kahuna Nudibranch and several others:  the Locust Nudibranch (Pease’s), the Violet Gill, and the Dot and Dash, all have similar long, narrow bodies and colours.  The Danielle’s seems to be much more common than the Kahuna (maybe because I have never seen one?) and we have found them in only a few feet of water on algae, sand and sponge-covered reef edges all over North Kihei and Ma’alaea Harbour, Maui.  Like the others, they have orange on their rhinophores and and an orange glow to translucent gills.  Look closely and you will see that the orange on the rhinophores is primarily posterior and NOT banded as they are on the Pease’s, Violet Gill and Dot & Dash. To about 1 inch or 25 mm.