Four species of algae growing on one chiton!
The chiton is on the left side, barely visible under the seaweeds (see close up below). Can you guess the four seaweeds?
(1) The large well-developed holdfast with a long stipe (stem) is Bull Kelp (Nereocystis luetkeana).
(2) The slightly darker brown algae above that, with a short stipe and wavy-edged blade is Feather Boa Kelp (Egregia menziesii).
(3) The smooth dark purple blade with some iridescence is Splendid Iridescent Seaweed (Mazzaella splendens).
(4) The bright green algae at the bottom is a type of sea lettuce, probably Ulva linza.
It's likely that the algae increases the drag forces that the chiton experiences, which might increase its risk of dislodgement. (Photos taken at the North Jetty near the entrance to Bodega Harbor.)
Although difficult to see, the chiton is probably Mopalia hindsii, one of the larger chitons in northern California. See the next photo of a different individual without algae. Note that the outer edge (called a "girdle" in chitons) is wide and relatively smooth.