P. quadrilineata on one of its encrusting bryozoan prey species, Membranipora membranacea, living on a Laminaria frond. On its right, the dorsal surface of the translucent foot is spread into view.
Colour form is common also on P. capitata but 15 lamellae on the rhinophore (visible in other photographs of this specimen) differentiates this as P. quadrilineata. Length 12.5 mm. Menai Strait, Wales. February 2011.