This barnacle has six wall plates which are sculpted with vertical tube-like ribs which extend downwards onto the rock in projections rather like the edge of a thatched roof.

This is a large species of barnacle and can grow to a diameter of 6 cm (2.4 in), but when densely packed together, individuals may be much taller than they are wide.

The base of the barnacle is little calcified so that when it is broken from the rock, a membrane and some soft tissues may be left behind.

[2] Like other acorn barnacles, S. cariosus is a filter feeder; when it is under water, the moveable terga at the apex part, and the cirri are extended to feed.

[3] Larger barnacles may be too big for the frilled dogwinkle (Nucella lamellosa), the purple seastar (Pisaster ochraceus) or the sunflower sea star (Pycnopodia helianthoides) to tackle.