[2] The body bears four pairs of longitudinal rows of cilia known as combs which extend about three quarters the length of the animal between its mouth and its aboral (opposite) end.

It is a pelagic species, occurring in open water, but is sometimes found in rock pools or washed up on the beach.

P. pileus remains motionless while it snares larger prey with its long tentacles, whereas B. infundibulum draws in a feeding current of water and filters out the smaller, more weakly swimming, tiny zooplankton.

[5] In the North Sea, P. pileus makes large daily vertical migrations as do its main copepod prey.

[4] These migrations do not take place in the winter and at this period, P. pileus remains close to the sediment, often with a cessation of movement of the combs of cilia.