Mopalioidea Dall 1889

The underside of this species is composed of a flat foot with a row of gills along each side (gills not visible in this photo). The edges of the mantle form a wide belt around the foot. Photographed by Dave Cowles at San Simeon, CA 1995

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.

Lepidochitona cinerea; Asgrauwe keverslak.

Another photo of the underside. Photo by Dave Cowles, San Simeon, CA April 1997 This species was formerly abundant at San Simeon, CA. During the latter years of the 1990's I (Dave Cowles) observed large numbers decomposing and washing up onto the beach. I suspect a disease was affecting them. Those washing ashore were blotched, as some living individuals are. I wonder if the blotching seen in living individuals is a sign of disease? Far fewer can be found there now.

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

Cryptochiton stelleri San Simeon, CA (Photo by: Dave Cowles, 1995)

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

lined chiton

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

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

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

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

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.

Tonicella insignis crawling on coralline algae. Photo by Kirt Onthank, August 2007