This venerable old chiton, just over 8 cm long, was also found at Sares Head. The head is to the right. The plates are so worn that the pattern can hardly be seen. The mantle color is unusual for this species but the mantle hairs are stiff and strap-like and both the Kozloff key and Aaron Baldwin's key identify it as Mopalia muscosa. The mantle and plates of this individual are also a whole city of symbionts, from several species of polychaete worms, small copepods, a tiny limpet (visible above at the top of plate 2), unidentified stalked invertebrates, and even a chironomid (midge fly) larva! I know that insects are rarely found in the ocean but the midge larva was clearly at home--crawling among other invertebrates and across the plates, nestling down in the edge of the mantle at the margin of the plates, etc., even though the chiton was fully immersed in seawater.
This closeup of the mantle of the individual above shows the strange yellowish background color of the mantle combined with the familiar thick, strap-like hairs characteristic of this species. The limpet is visible on the edge of the algae-encrusted plate at the bottom right, and a mucus tube of a polychaete worm is visible at the margin between the plate and the mantle. A few strands of red algae intertwine among the mantle hairs.
Here is a view of the underside of the above individual. The mouth is clearly visible on the left. The large central region is the foot, which has several strands of mucus on it. The ring around the foot is the mantle cavity, which contains the gills. The outer ring of tissue is the underside of the mantle (girdle), which is held down fairly tightly against the substrate.
