Modocia Modocia was a Cambrian trilobite known from North America. Like Athabaskia , it had prominent backward pointing spines and was larger than many other trilobites. Bivalves are a group of mollusks that includes clams, mussels, oysters and scallops. They are so named because their shell consists of two halves, or valves, that are hinged together. Usually the two halves are mirror images of each other, although this is not always the case.
Bivalves have small heads that consist of little more than a mouth.
Most of them burrow in soft mud, burying themselves out of the reach of predators, and draw food and water into their shell through long snorkel-like siphons. See also Trilobites Monograptus Monograptus was a graptolite with a single stalk and a single row of cups. It is among the best known graptolites. See also Graptolites Monotis Monotis is a thin shelled bivalve with very noticeable radiating ribs. It occurs in Upper Triassic rocks around the world.