Left: April 2012. Dorset, England. H. bifida body is translucent whitish with a reddish digestive gland forming a longitudinal band on each side connecting the bases of the cerata and extending into the cerata to their apices. Varying amounts of red pigment elsewhere on the body. Enrolled rhinophores have variable amounts of red pigment. The red colour is usually sufficient to distinguish this species from P. dendritica.
Right August 1975. Orkney. Specimen of H. bifida found on a sublittoral Laminaria frond. This is not a food alga of H. bifida, so the specimen is unfed, has lost the diagnostic colour of the red algae it feeds on and might be mistaken for P. dendritica.

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