Members of the Phylum Mollusca contain a variety of common characteristics. Some common characteristics include a soft body surrounded by some sort of an outer shell secreted by the mantle. The shell may be external or internal or secondarily lost. A strong muscular foot used for locomotion is another common characteristic of the Phylum Mollusca. The molluscs are extremely large in species numbers, approximately 300-400 species of molluscs occur in the intertidal zone of Southern California. The Chitons belong to the Class Polyplacophora, whose members can distinguished by eight calcareous plates which are embedded on a muscular girdle. Several gills are located on either side of the foot which serve for respiration. The girdle may contain scales, hairs or granules on its surface. Chitons are herbivores, feeding mostly on algae. Chiton fossils date back as far as half a billion years ago, with a increase in diversity since then. The Order Neoloricata
- Genus Mopalia
- Species Muscosa
The chitons can be divided into three Families, the Ischnochitonidae, Callistoplacidae and the Mopalidae. The Family Ischnochitonidae contains the Lepidochitona hartwegii and can be distinguished from other families from its scaley girdle and a variety of valve patterns. Members of the Genus Lepidochitona are characterized by a flat, depressed tail valve. The Family Callistoplacidae can be distinguished by spines or spicules on the girdle and once again the valves can have a variety of patterns. The members of the Genus Nutallina can be separated from other genera by 9 to 12 slits in the head valve and long, smooth insertion plates. The Family Mopalidae can be separated from other families by long hairs or spicules on the girdle. The Genus Mopalia has a notched tail valve with a single pair of slits on either side.
Chitons occupy a great range from high in the intertidal zone to depths of over 12,000 feet, and from the tropics to the polar seas. They become most abundant on temperate rocky shores because that's where they can find a hard substratum for attachment by their well-adapted broad foot, and it's also the place where their foods are the most abundant. Some chiton species occupy the outer coast because they are able to withstand the buffeting of heavy surf, but others occupy the quieter area behind the offshore reefs or rocks, in embayments, and in tidepools.
About 20% of all chitons can be found along the west coast from Alaska all the way down to southern California, which is more than any other coasts in the world. Fifty species and subspecies are found in Monterey Bay alone. A large and diverse chiton population is also found in New Zealand and Australia.
Chitons are generally sluggish and many are nocturnal and remain concealed under rocks during the day, therefore their foods mainly consist of algal films scraped off the rocks by the radula, but some also consume animal matters. More importantly, the diets of individuals of any one species may differ in different habitats.
Lepidochitona hartwegii: it is always found associated with Pelvetia fastigiata, which is the principle diet for the chiton. This chiton in found in southern California in the mid-tide zone at the rocky shores, especially at Little Corona and Palos Verdes.
Nuttalina fluxa: The coralline algae is the principle food for this chiton. They have sea gulls that prey on them. This species is the most frequently encountered in southern California, and they live in pits in the rocks in the mid- and upper-tide horizon all all rocky shores and some of the rock jetties in southern California. They live in depressions which are about the shape and size of the animal, and the depressions are exposed at low tide. Often the depressions are so deep that the back of the chiton is below the surrounding rock, thus they have become sessile in habitat, sacrificing grazing habitat for greater protection. The modifications in habits and habitat assure the species to perpetuate. This species of chiton is mainly preyed upon by western gulls. In some localities as much as 15 percent of the chiton population are taken during western gull's breeding season.
Mopalia muscosa: this species maintains a home where it emerges at night to feed on the algae; it travels as far as 2 feet from its home and it will return. They are common in southern California marine habitats. It is found in the mid-tide zone generally within rock crevices among barnacles, and it has also been collected from the boat floats of the principal bays and harbors of southern California. This species is most common on rocks and in tidepools, middle and low intertidal zones in regions of low to moderate surf; they have a big range from Queen Charlotte Islands (British Columbia) to Isla Cedros (Baja California). The mossy chiton is also one of the few west coast species that does well in estuaries. They remain in place during the day or whenever exposed by low tides. Individuals living permanently submerged in tidepools did not have the same homing behavior. The chiton feed mainly on the red algae Gigartina papillata and Endocladia muricata and the green alga Cladophora whenever they are available, but in other places the species appear to be unselective herbivores, and the gut can contain animal matter for up to 15%
Lepidochitona hartwegii (Gray, 1821). Common name-Hartweg's Chiton. Previous name- Cyanoplax hartwegii. The Hartweg's chiton has a bright blue interior of valves and an oval shaped dark green to grey body. This species often grows to a length of two inches. The Hartweg's chiton is granulated on the surface of the girdle and the valves often have a white streak along the posterior end. This species is found in the mid-tidal zones on or under rocks from Monterey, Ca to Baja California.
Nuttalina fluxa (Dall, 1871). Common name- Califronia Chiton or Rough chiton. The California chiton can be distinguished by its small size which is usually 1.5 inches or less in length. The girdle is often brown to pink in color and has several spines on it. The California chiton is found in pits in the rocks in the upper and mid-tidal zone and on many rock jetties in Southern California. This species of chiton is the most common in Southern California.
Mopalia muscosa (Gray, 1847). Common name- Mossy Chiton. The mossy chiton is often much larger then the California Chiton. The Mossy Chiton can grow to a length of 2.5 inches. The shell is often dull gray to black and the girdle contains stiff curled hairs. The mossy chiton is found in rock crevices in the mid tide zone and the range is from Alaska to Baja California.
1. Shape of organism is oval, flattened; color is grayish green; tail valve is depressed; found on or under rocks or under algae intertidally...................Lepidochitona hartwegii
2. Nine to twelve slits in the head valve; long smooth insertion plates; found on rocks in the intertidal zone............................Nuttallina fluxa
3. Shape of organism is oval, flat; color varies from dull brown to dark olive or gray; the stiff mossy tails on the girdle is a common feature; tail valve notched behind, with a pair of slits at sides; found on rocks in intertidal zone protected from heavy wave action or in tide pools...............................Mopalia muscosa