P. ulvae habitats.
Left: Probably over a million P. ulvae, with tracks in foreground, on wet sand of a small part of the Dee Estuary, Cheshire. When the surface dries they withdraw from sight below it. © P. Topley.
Right: Much of the mud on the Severn Estuary is too soft for P. ulvae to crawl on, but they may be overlooked when they lie buried with just their heads and feet protruding to feed on the surrounding surface. Many were found in this wet mud near high water mark where the glistening bodies were initially mistaken for Limapontia depressa sea slugs.