Mopaliinae Dall 1889

The chitons' eight plates differentiate them from all other molluscs. These omnivores spawn grey-green eggs, and fertilization occurs externally. Miniature adults form by sixteenth day.

This chiton is known to feed on algae; here it is seen on the green alga Ulva.

This individual was on the rocky head on the south side of Bowman Bay. Photo by Dave Cowles, July 2008

The head plate (plate 1, seen here) is about the same width as plate 8, and the girdle is about the same width in front as on the sides. The girdle has neither scales nor tubercles, but it does have fine, scattered hairs which are so fine and sparse that it is hard to see them except along the edges.

This 10 cm individual was between several boulders on Sares Head, April 2011. Photo by Dave Cowles

The girdle hairs are sparse and fine. They can hardly be seen except, for example, here along the edge of the mantle at high magnification. The fine filaments which sprout from the hairs are often in two rows of curved, diverging bristles on opposite sides of the main hair and have a glassy spicule on the end. Photo by Dave Cowles, August 2012

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.

Mopalia swanii, about 5 cm long. Anterior end is to the right. (Photo by: Dave Cowles, August 2012 )

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.

Another view of Mopalia lignosa. Note the hairs between the plates. Photo by Dave Cowles, San Simeon, CA 1997

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.

Mopalia lignosa, San Simeon, CA (Photo by: Dave Cowles, 1997)

Mopalia muscosa under a rock at San Simeon, CA. Length is about 3 cm. Head and plate 1 are to the left. (Photo by: Dave Cowles, 1995)

Dendrochiton flectens, underwater photo (Photo and identification by: Aaron Baldwin)

This larger view shows how the chiton is grazing the sponge off the scallop.

This closeup shows the detail on the plates, plus a view of some of the girdle.

These chitons are omnivorous. This individual could well have been feeding on the adjacent bryozoan.

The anterior two plates of this individual have a lot of white.