Appearance
The body of Facelina bostoniensis is translucent white with a pink coloured hue around the mouth. The oesophagus, situated just behind the rhinophores, is clearly visible as a curved red tube. There are some patches of white pigment on the head, between the rhinophores and down the tail of the animal. Some individuals have blue iridescence in small areas around the head and rarely specimens with extensive blue colouration are found. The rhinophores are annulate, the oral tentacles are very long, both sets of tentacles are tipped with white pigment. Large individuals may grow to approximately 55 mm in length.